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CThe Building Regulations 2000

Site preparation and resistance tocontaminants and moisture

APPROVED DOCUMENTC1 Site preparation and resistance to contaminantsC2 Resistance to moisture

2004

EDIT

ION

MAIN CHANGES IN THE 2004 EDITION

This edition of Approved Document C, Sitepreparation and resistance to contaminantsand moisture, replaces the 1992 (with 2000amendments) edition. The main changes are:

C1 Site preparation and resistance tocontaminants

Site preparation

a) Site investigation is now recommended asthe method for determining how muchunsuitable material should be removed.

Resistance to contaminants

b) Requirement C1(2) now applies to materialchange of use as set out in Regulations 5 and6.

c) Remedial measures for dealing with landaffected by contaminants have been expandedto include biological, chemical and physicaltreatment processes.

d) The area of land that is subject to measuresto deal with contaminants now includes theland around the building.

e) Guidance on protection from radon isexpanded to include buildings other thandwellings.

Sub-soil drainage

f) Guidance is included relating to sub-soildrainage and the risk of transportation ofwater-borne contaminants.

Approved Document CSite preparation and resistance to contaminants and moisture

C2 Resistance to moisture

g) New guidance recommends that in order toreduce the condensation risk to floors, wallsand roofs reference should be made to therevised BS 5250 and “Limiting thermal bridgingand air leakage: robust details” and BR 262“Thermal insulation: avoiding risks.”

h) Guidance is now provided on the use ofmoisture resistant boards for the flooring inbathrooms, kitchens and other places wherewater may be spilled from sanitary fittings orfixed appliances.

i) Reference is made to BS 8208 for assessingthe suitability of cavity walls for filling togetherwith the map and table in BR 262.

j) Interface between walls and doors andwindows. Check rebates are nowrecommended in the most exposed parts of thecountry.

k) New guidance points to the need for betterattention to detail in exposed areas where levelaccess is provided to support Part M, Accessto and use of buildings to ensure adequateprovision is made for resistance to moisture.

l) Former Requirement F2; Condensation inroofs, has been transferred to Part C as it dealswith effects on the building fabric rather thanventilation for the health of occupants.

PAGE

Use of Guidance 3

The Requirements 5

Material change of use 6

Interpretation (Regulation 2) 6

Meaning of material change of use (Regulation 5) 6

Requirements relating to material change ofuse (Regulation 6) 6

Historic buildings 7

Section 0: General 9

Performance 9

Introduction to provisions 9

Flood risk 9

Land affected by contaminants 10

Authorities that should be notified aboutcontamination 10

Definitions 11

Section 1: Clearance or treatment of unsuitable material 12

Site investigation 12

Unsuitable material 12

Section 2: Resistance to contaminants 14

Introduction 14

Solid and liquid contaminants 15

Risk assessment 15

Remedial measures 17

Risks to buildings, building materials andservices 18

Methane and other gases from the ground 19

Introduction 19

Risk assessment 19

Remedial measures 20

Radon 21

Section 3: Sub-soil drainage 22

Section 4: Floors 24

Ground supported floors (moisture from the ground) 24

Technical solution 24

Alternative approach 25

Suspended timber ground floors (moisture from the ground) 25

PAGE



Suspended concrete ground floors (moisture from the ground) 27


Ground floors and floors exposed from below (resistance to damage from interstitial condensation) 28

Floors (resistance to surface condensation and mould growth) 28

Section 5: Walls 29

Internal and external walls (moisture from the ground) 29



External walls (moisture from the outside) 31

Solid external walls 31



Cavity external walls 32



Cavity insulation 32

Framed external walls 36

Cracking of external walls 36

Impervious cladding systems for walls 36



Joint between doors and windows 37

Door thresholds 37

External walls (resistance to damage frominterstitial condensation) 38

External walls (resistance to surfacecondensation and mould growth) 38

Section 6: Roofs 39

Roofs (resistance to moisture from the outside) 39



Roofs (resistance to damage from interstitialcondensation) 40

Roofs (resistance to surface condensation and mould growth) 40

Contents

1

C

Approved Document C Site preparation and resistance to contaminants and moisture

PAGE

British Standards referred to 41

Other documents referred to 42

Annex A: Guidance on the assessment ofland affected by contaminants 45

References to Annex A 45

DIAGRAMS

1. Distribution of shrinkable clays andprincipal sulfate/sulfide bearing strata in England and Wales 13

2. Example of a conceptual model for a site showing source-pathway-receptor 15

3. Subsoil drain cut during excavation 23

4. Ground supported floor-construction 25

5. Suspended timber floor – construction 26

6. Suspended floor – preventing watercollection 26

7. Typical floors exposed from below 28

8. Damp proof courses 30

9. Protecting inner leaf 30

10. Protection of wall head from precipitation 31

11. Insulated external walls: examples 33

12. UK zones for exposure to driving rain 34

13. Windows reveals for use in areas ofsevere or very severe exposure to driving rain 37

14. Accessible threshold for use in exposed areas 38

A1. The process of managing land affected by contaminants 47

TABLES

1. Volume change potential for somecommon clays 13

2. Examples of sites likely to containcontaminants 14

3. Examples of possible contaminants 17

4. Maximum recommended exposure zones for insulated masonaty walls 35

Approved Document CSite preparation and resistance to contaminants and moisture2

C CONTENTS

THE APPROVED DOCUMENTSThis document is one of a series that has beenapproved by the First Secretary of State for thepurpose of providing practical guidance withrespect to the requirements of Schedule 1 toand Regulation 7 of the Building Regulations2000 (SI 2000/2531) for England and Wales. SI2000/2531 has been amended by the Building(Amendment) Regulations 2001 (SI 2001/3335),by the Building (Amendment) Regulations 2002(SI 2002/440), by the Building (Amendment)(No. 2) Regulations 2002 (SI 2002/2871), by theBuilding (Amendment) Regulations 2003 (SI2003/2692) and by the Building (Amendment)Regulations 2004 (SI 2004/1465).

At the back of this document is a list of allthe documents that have been approved andissued by the First Secretary of State for thispurpose.

Approved Documents are intended to provideguidance for some of the more commonbuilding situations. However, there may well bealternative ways of achieving compliance withthe requirements. Thus there is no obligationto adopt any particular solution contained inan Approved Document if you prefer to meetthe relevant requirement in some other way.

Other requirementsThe guidance contained in an ApprovedDocument relates only to the particularrequirements of the Regulations which thedocument addresses. The building work willalso have to comply with the Requirements ofany other relevant paragraphs in Schedule 1 tothe Regulations.

There are Approved Documents which giveguidance on each of the Parts of Schedule 1and on Regulation 7.

LIMITATION ON REQUIREMENTSIn accordance with Regulation 8, therequirements in Parts A to D, F to K and N(except for paragraphs H2 and J6) of Schedule1 to the Building Regulations do not requireanything to be done except for the purpose ofsecuring reasonable standards of health andsafety for persons in or about buildings (andany others who may be affected by buildings ormatters connected with buildings).

The requirements in Part C address health andsafety, and do not seek to protect the buildingfabric for its own sake. Thus the degree ofprecautions needed to comply with Part C willbe influenced by the intended use of thebuilding. Part C may not apply where it can bedemonstrated that it will not serve to increasethe protection to the health and safety of any

persons habitually employed in the building inquestion.

Paragraphs H2 and J6 are excluded fromRegulation 8 because they deal directly withprevention of the contamination of water. PartsE and M (which deal, respectively, withresistance to the passage of sound, andaccess to and use of buildings) are excludedfrom Regulation 8 because they address thewelfare and convenience of building users. PartL is excluded from Regulation 8 because itaddresses the conservation of fuel and power.All these matters are amongst the purposes,other than health and safety, that may beaddressed by Building Regulations.

MATERIALS AND WORKMANSHIPAny building work which is subject to therequirements imposed by Schedule 1 to theBuilding Regulations should, in accordancewith Regulation 7, be carried out with propermaterials and in a workmanlike manner.

You may show that you have complied withRegulation 7 in a number of ways. Theseinclude the appropriate use of a productbearing CE marking in accordance with theConstruction Products Directive (89/106/EEC)1

as amended by the CE Marking Directive(93/68/EEC)2, or a product complying with anappropriate technical specification (as definedin those Directives), a British Standard, or analternative national technical specification ofany state which is a contracting party to theEuropean Economic Area which, in use, isequivalent, or a product covered by a nationalor European certificate issued by a EuropeanTechnical Approval issuing body, and theconditions of use are in accordance with theterms of the certificate. You will find furtherguidance in the Approved Documentsupporting Regulation 7 on materials andworkmanship.

Independent certification schemesThere are many UK product certificationschemes. Such schemes certify compliancewith the requirements of a recogniseddocument which is appropriate to the purposefor which the material is to be used. Materialswhich are not so certified may still conform toa relevant standard.

Many certification bodies which approve suchschemes are accredited by UKAS.

Use of Guidance

Site preparation and resistance to contaminants and moistureApproved Document C3

CTHE BUILDING REGULATIONS 2000

1 As implemented by the Construction ProductsRegulations 1991 (SI 1991/1620).

2 As implemented by the Construction Products(Amendment) Regulations 1994 (SI 1994/3051).

Technical specificationsUnder section 1(a) of the Building Act, BuildingRegulations may be made for various purposesincluding health, safety, welfare, convenience,conservation of fuel and power, and preventionof contamination of water. Standards andtechnical approvals are relevant guidance tothe extent that they relate to theseconsiderations. However, they may alsoaddress other aspects of performance such asserviceability, or aspects which, although theyrelate to the purposes listed above, are notcovered by the current Regulations.

When an Approved Document makes referenceto a named standard, the relevant version ofthe standard is the one listed at the end of thepublication. However, if this version has beenrevised or updated by the issuing standardsbody, the new version may be used as a sourceof guidance provided it continues to addressthe relevant requirements of the Regulations.

The appropriate use of a product whichcomplies with a European Technical Approvalas defined in the Construction ProductsDirective will meet the relevant requirements.

The Office intends to issue periodicamendments to its Approved Documents toreflect emerging harmonised EuropeanStandards. Where a national standard is to bereplaced by a European harmonised standard,there will be a co-existence period duringwhich either standard may be referred to. Atthe end of the co-existence period, the nationalstandard will be withdrawn.

THE WORKPLACE (HEALTH,SAFETY AND WELFARE)REGULATIONS 1992The Workplace (Health, Safety and Welfare)Regulations 1992 contain some requirementswhich affect building design. The mainrequirements are now covered by the BuildingRegulations, but for further information seeWorkplace health, safety and welfare.Workplace (Health, Safety and Welfare)Regulations 1992. Approved Code of PracticeL24. Published by HSE Books 1992; ISBN (07176 0413 6).

The Workplace (Health, Safety and Welfare)Regulations 1992 apply to the common parts offlats and similar buildings if people such ascleaners and caretakers are employed to workin these common parts. Where therequirements of the Building Regulations thatare covered by this Part do not apply todwellings, the provisions may still be requiredin the situations described above in order tosatisfy the Workplace Regulations.


C THE BUILDING REGULATIONS 2000

This Approved Document deals with thefollowing Requirements which are contained inthe Building Regulations 2000 (as amended bySI 2001/3335, SI 2002/440, SI 2002/2871 andSI 2003/2692.

The Requirements


CTHE BUILDING REGULATIONS 2000

Site preparation and resistance to contaminants and moisture

Preparation of site and resistance to contaminants.

C1. (1) The ground to be covered by the building shall be reasonablyfree from any material that might damage the building or affect itsstability, including vegetable matter, topsoil and pre-existingfoundations.

(2) Reasonable precautions shall be taken to avoid danger to health andsafety caused by contaminants on or in the ground covered, or to becovered by the building and any land associated with the building.

(3) Adequate sub-soil drainage shall be provided if it is needed toavoid-

(a) the passage of ground moisture to the interior of the building;

(b) damage to the building, including damage through thetransport of water-borne contaminants to the foundations ofthe building.

(4) For the purpose of this requirement, “contaminant” means anysubstance which is or may become harmful to persons or buildingsincluding substances, which are corrosive, explosive, flammable,radioactive or toxic.

Resistance to moisture

C2. The floors, walls and roof of the building shall adequately protectthe building and people who use the building from harmful effectscaused by:

(a) ground moisture;

(b) precipitation and wind-driven spray;

(c) interstitial and surface condensation; and

Requirement Limits on application

MATERIAL CHANGE OF USERequirement C1 (2), which addressesresistance to contaminants, is now added tothe requirements in Regulation 6 of the BuildingRegulations 2000 which should be compliedwith when there are certain material changes ofuse of buildings. Regulation 6 sets out whichparts of Schedule 1 should be complied withwhen there is a material change of use of thebuilding as defined in Regulation 5. Theabsence of such a requirement would havemeant that occupiers of buildings in areas atrisk from contaminants may remain unprotectedafter the building work to effect the change ofuse is complete.

In particular, some contaminants can penetratethe floors of buildings such as landfill gasarising from the deposition of waste andvapours from spills of organic solvents andfuel. These contaminants can also migratelaterally from land outside the building. In orderto deal with this Requirement C1 (2) nowapplies to all changes of use that have aresidential purpose or provide sleepingaccommodation including hotels, i.e. asdefined by Regulation 5 (a) to 5 (g) with theexception of 5 (e) public buildings and 5 (j)shops. Other types of buildings are covered byHealth and Safety legislation so do not needaddressing through the Building Regulations,for example workplace assessment, includingradon measurements.

Attention is drawn to the following extractsfrom The Building Regulations 2000 (asamended by SI 2001/3335, SI 2002/440, SI 2002/2871, SI 2003/2692 and SI 2004/1465.

Interpretation (Regulation 2)“Room for residential purposes” means a room,or suite of rooms, which is not a dwelling-house or flat and which is used by one or morepersons to live and sleep in, including rooms inhotels, hostels, boarding houses, halls ofresidence and residential homes but notincluding rooms in hospitals, or other similarestablishments, used for patientaccommodation.

Meaning of material change ofuse (Regulation 5)For the purposes of paragraph 8 (1)(e) ofSchedule 1 to the Act and for the purposes ofthese Regulations, there is a material change ofuse where there is a change in the purposes forwhich or the circumstances in which a buildingis used, so that after the change:

a) the building is used as a dwelling, wherepreviously it was not;

b) the building contains a flat, wherepreviously it did not;

c) the building is used as an hotel orboarding house, where previously it was not;

d) the building is used as an institution,where previously it was not;

e) the building is used as a public building,where previously it was not;

f) the building is not a building described inClasses I to VI in Schedule 2, where previouslyit was;

g) the building, which contains at least onedwelling, contains a greater or lesser number ofdwellings than it did previously;

h) the building contains a room forresidential purposes, where previously it didnot;

i) the building, which contains at least oneroom for residential purposes, contains agreater or lesser number of such rooms than itdid previously; or

j) the building is used as a shop, wherepreviously it was not.

Requirements relating to materialchange of use (Regulation 6)(1) Where there is a material change of useof the whole of a building, such work, if any,shall be carried out as is necessary to ensurethat the building complies with the applicablerequirements of the following paragraphs ofSchedule 1:

(a) in all cases,

B1 (means of warning and escape)

B2 (internal fire spread - linings)

B3 (internal fire spread - structure)

B4 (2) (external fire spread-roofs)

B5 (access and facilities for the fireservice)

C1 (2) (resistance to moisture)

F1 (ventilation)

G1 (sanitary conveniences and washingfacilities)

G2 (bathrooms)

H1 (foul water drainage)

H6 (solid waste storage)

J1 to J3 (combustion appliances)

L1 (conservation of fuel and power -dwellings);

L2 (conservation of fuel and power -buildings other than dwellings);

(b) in the case of a material change of usedescribed in regulations 5(c), (d), (e) or (f), A1to A3 (structure);



(c) in the case of a building exceeding fifteenmetres in height, B4 (1) (external fire spread -walls);

(d) in the case of material change of usedescribed in regulation 5(a), C2 (resistance tomoisture);

(e) in the case of a material change of usedescribed in regulation 5(a), (b), (c), (g), (h) or (i)E1 to E3;

(f) in the case of a material change of usedescribed in regulation 5(e), where the publicbuilding consists of or contains a school, E4(acoustic conditions in schools);

(g) in the case of a material change of usedescribed in regulation 5 (c), (d), (e), or (j), M1(access and use);

(h) in the case of a material change of usedescribed in regulation 5 (a), (b), (c), (d), (f) - ifit provides new residential accommodation, (g),(h), or (i), C1 (2) (resistance to contaminants).

(2) Where there is a material change of useof part only of a building, such work, if any,shall be carried out as is necessary to ensurethat –

(a) that part complies in all cases with anyapplicable requirement referred to in paragraph(1) (a);

(b) in a case to which sub-paragraphs (b),(d), (e) or (f) of paragraph (1) apply, that partcomplies with the requirements referred to inthe relevant sub-paragraphs; and

(c) in the case to which sub-paragraph (c) orof paragraph (1) applies, the whole buildingcomplies with the requirement referred to inthat sub-paragraph; and

(d) in the case to which sub-paragraph (g) ofparagraph (1) applies –

i) that part and any sanitary appliancesprovided in or in connection with therequirements referred to in that sub-paragraph; and

ii) the building complies with requirementM1 (a) of Schedule 1 to the extent thatreasonable provision is made toprovide either suitable independentaccess to the part or suitable accessthrough the building to that part; and

(e) in the case to which sub-paragraph (g) orof paragraph (1) applies, the whole buildingcomplies with the requirement referred to inthat sub-paragraph.

Historic buildingsMaterial change of use or alterations to existingbuildings may include work on historicbuildings. Historic buildings include:

a) listed buildings;

b) buildings situated in conservation areas;

c) buildings which are of architectural andhistorical interest and which are referred to asa material consideration in a local authority’sdevelopment plan;

d) buildings of architectural and historicalinterest within national parks, areas ofoutstanding natural beauty and world heritagesites.

The need to conserve the specialcharacteristics of such historic buildings needsto be recognised3. In such work, the aim shouldbe to improve resistance to contaminants andmoisture where it is practically possible, alwaysprovided that the work does not prejudice thecharacter of the historic building, or increasethe risk of long-term deterioration to thebuilding fabric or fittings. In arriving at anappropriate balance between historic buildingconservation and improving resistance tocontaminants and moisture it would beappropriate to take into account the advice ofthe local planning authority’s conservationofficer.

Particular issues relating to work in historicbuildings that warrant sympathetic treatmentand where advice from others could thereforebe beneficial include the following:

a) Avoiding excessively intrusive gasprotective measures;

b) Ensuring that moisture ingress to the roofstructure is limited and the roof can breathe4.Where it is not possible to provide dedicatedventilation to pitched roofs it is important toseal existing service penetrations in the ceilingand to provide draught proofing to any lofthatches. Any new loft insulation should be keptsufficiently clear of the eaves so that anyadventitious ventilation is not reduced.


CTHE BUILDING REGULATIONS 2000 C

3 BS 7913: 1998 Guide to the principles of theconservation of historic buildings. Provides guidanceon the principles that should be applied whenproposing work on historic buildings.

4 SPAB Information Sheet 4 The need for old buildings tobreathe, 1986

In most cases the rate at which gas seeps intobuildings, mainly through floors, can bereduced by edge located sumps or sub-floorvents. These are less intrusive than internalsumps or ducts that may involve taking upfloors. If flagged floors are taken up the stonesshould be indexed and their layout recorded tofacilitate relaying when work is completed5.

Radon can be dispersed by ventilationstrategies such as positive pressurisation.These systems can often be accommodated inan unobtrusive manner.

If internal mechanical ventilation is used todisperse ground gases, it may affect thefunctioning of combustion appliances and maylead to the spillage of products of combustioninto the building. Guidance on this can befound in Good Building Guide 25 Buildings andradon6.



5 BRE Report BR 267 Major alterations and conversions:a BRE guide to radon remedial actions in existingbuildings, 1994

6 BRE GBG 25 Buildings and radon, 1996

Performance

C1

0.1 In the First Secretary of State’s view therequirements of C1 will be met by makingreasonable provisions to secure the health andsafety of persons in and about the building,and by safeguarding them and buildingsagainst adverse effects of:

a) unsuitable material including vegetablematter, top soil and pre-existing foundations;

b) contaminants on or in the groundcovered, or to be covered, by the building andany land associated with the building; and

c) groundwater.

C2

0.2 In the First Secretary of State’s view therequirements of C2 will be met if the floors,walls and roof are constructed to protect thebuilding and secure the health and safety ofpersons in and about the building from harmfuleffects caused by:

a) moisture emanating from the ground orfrom groundwater;

b) precipitation and wind-driven spray;

c) interstitial and surface condensation; and

d) spillage of water from or associated withsanitary fittings and fixed appliances.

Introduction to provisions0.3 Sections 1, 2 and 3 of this documentcover Requirement C1 and deal with sitepreparation and resistance to contaminantsunder the headings “Clearance or treatment ofunsuitable material”, “Resistance tocontaminants” and “Sub-soil drainage”.Building Regulations are made for the purposesof securing the health, safety, welfare andconvenience of persons in and about buildings.This means that action may need to be takento mitigate the effects of contaminants withinthe land associated with the building as well asprotecting the building and persons in andabout the building.

0.4 Hazards associated with the ground mayinclude the effects of vegetable matterincluding tree roots. They may include healthhazards associated with chemical andbiological contaminants, and gas generationfrom biodegradation of organic matter. Hazardsto the built environment can be physical,chemical or biological. Items such asunderground storage tanks or foundations maycreate hazards to both health and the building.Physical hazards also include unstable fill orunsuitable hardcore containing sulfate.

0.5 In addition, the naturally occurringradioactive gas radon and gases produced bysome soils and minerals can be a hazard.

0.6 Sections 4, 5 and 6 of this documentcover Requirement C2 and deal with resistanceto moisture under the headings ‘Floors’, ‘Walls’and ‘Roofs’. Moisture can rise from the groundto damage floors and the base of walls on anysite, although much more severe problems canarise in sites that are liable to flooding. Drivingrain or wind driven spray from the sea or otherwater bodies adjacent to the building canpenetrate walls or roofs directly, or throughcracks or joints between elements, anddamage the structure or internal fittings orequipment. Surface condensation from thewater vapour generated within the building cancause moulds to grow which pose a healthhazard to occupants. Interstitial condensationmay cause damage to the structure. Spills andleaks of water, in rooms where sanitary fittingsor fixed appliances that use water are installed(eg bathrooms and kitchens), may causedamage to floor decking or other parts of thestructure.

0.7 The diagrams in this Approved Documenthave been set out to show typical situationsand relationships between adjacent elements ofconstruction. Conventional notations andhatching have been used to identify differentmaterials. However, the diagrams cannotshow specific situations. It remains theresponsibility of the designer and builder toensure that the building work meets allrelevant aspects of the Building Regulations.

Flood risk

0.8 There is a presumption in planningguidance7 that development should not takeplace in areas that are at risk of flooding. Floodresistance is not currently a requirement inSchedule 1 of the Building Regulations 2000.However, when local considerationsnecessitate building in flood prone areas thebuildings can be constructed to mitigate someeffects of flooding such as:

a) Elevated ground water levels or flow ofsub-soil water across the site – this can bealleviated by the provision of adequate sub-soildrainage (see Section 3);

b) Sewer flooding due to backflow orsurcharging of sewers or drains - this can beaddressed through the use of non-return valvesand anti-flooding devices (see Section 3,paragraph 3.6);

Section 0: General


CGENERAL

7 Planning Policy Guidance Note PPG 25 Developmentand flood risk, DTLR, 2001

c) Intrusion of groundwater through floors –this can be addressed through the use of waterresistant construction (see Section 4,paragraphs 4.7 to 4.12);

d) Entry of water into floor voids – provisionto inspect and clear out sub-floor voids can beconsidered (see Section 4, paragraph 4.20);

Further information on flood resistantconstruction can be found in a number ofpublications 8,9,10.

Land affected by contaminants

0.9 The guidance given on resistance tocontaminants in Section 2 is for the purposesof the Building Regulations and theirassociated requirements. Users of thisdocument should be aware that there may befurther provisions for dealing with contaminantscontained in planning guidance or legislationmade under the regime set out in Part IIA ofthe Environmental Protection Act 1990 whichmay be supplementary to the requirements ofthe Building Regulations. The ContaminatedLand (England) Regulations 2000 make detailedprovisions of a procedural nature to help givefull effect to the Part IIA regime, and thestatutory guidance provides a basis forenforcing authorities to apply the regime.Where contaminants are removed, treated orcontained as part of the construction works,waste management law may apply. If waste isremoved for off-site disposal, the ‘Duty ofCare’ and/or special waste requirements11 willapply.

0.10 Redevelopment is often the mosteffective means of remediating land affected bycontaminants. This process is subject tocontrols under the Town and Country PlanningActs, and Local Planning Authorities follow theguidance in PPG 2312. Although environmentalprotection, planning and Building Regulationshave different purposes their aims are similar.Consequently the processes for assessing theeffects of pollutants and contaminants aresimilar. An investigation or assessment todetermine the characteristics of a site can befurther developed for Building Regulationspurposes when the form and construction ofthe buildings are known. If appropriate data aregathered at the early stages it should not benecessary to completely re-evaluate a site forBuilding Regulations purposes.

Authorities that should be notified aboutcontamination

0.11 Other regulatory authorities may have aninterest in land affected by contamination. Itmay be necessary at any stage of the siteinvestigation, risk assessment or remediationprocess to notify any unexpected events orchange in outcomes to these regulatoryauthorities. The most likely situations are:

• The Environmental Health department ofthe district council should be informed ifcontaminants are found on a site wherethe presence of contamination has notbeen formally recognised through theplanning process, if it is found thatcontaminants from the site are affectingother land or if contaminants are reachingthe site from neighbouring land.Additional discussions may also berequired if the contamination identifieddiffers from that which has beenpreviously discussed and agreed with thelocal planning authority (LPA) orEnvironmental Health department.

• As redevelopment is the most favouredmeans of dealing with land affected bycontaminants, all land quality issuesshould be set out in documents insupport of planning approval sent to thelocal planning authority. As designs arerefined it may be necessary to inform theLPA of any impacts the design changesmay have on the risk assessment andremediation strategy.

• The Environment Agency has a number ofrelevant duties at sites wherecontamination may be an issue; inparticular these include specific dutiesrelating to waste management and theprotection of water quality and resources.Sites may be of concern to theEnvironment Agency where there is apotential impact on controlled waters, ifthe site is designated as a Special Siteunder Part IIA of the EnvironmentalProtection Act 1991, where anauthorisation may be required or specifichazards are found. The local EnvironmentAgency office should be contacted toidentify if there are any relevant issues.

• Some remedial measures may themselvesrequire prior authorisation from theEnvironment Agency includingabstraction licensing for groundwatertreatment and waste managementlicensing for a number of activitiesinvolving contaminated soils.


C GENERAL

8 Preparing for floods: interim guidance for improving theflood resistance of domestic and small businessproperties, DTLR, 2002

9 BRE for Scottish Office Design guidance on flooddamage for dwellings, TSO, 1996

10 CIRIA/ Environment Agency Flood products. Usingflood protection products – a guide for home owners,2003. Available from: www.ciria.org/flooding

11 Environmental Protection (Duty of Care (England))Regulations 1991, as amended, (SI 1991/2839 and SI2003/63).

12 Planning Policy Guidance Note PPG 23 Planning andpollution control, ODPM, 1997

• Working on contaminated land can behazardous. The risks should be assessedto meet the requirements of theConstruction (Design and Management)Regulations 1994. Working proceduresshould be in accordance with theConstruction (Health, Safety and Welfare)Regulations 1996. It may be necessary togive notice to the Health and SafetyExecutive prior to work starting.

Specific guidance on the assessment of landaffected by contaminants is set out inAppendix A.

Definitions

0.12 The following meanings apply to termsthroughout this Approved Document:

Building and land associated with thebuilding. The building and all the land formingthe site subject to building operations whichincludes land under the building and the landaround it which may have an effect on thebuilding or its users. (see also paragraph 2.11).

Contaminant. Any substance13 which is or maybecome harmful to persons or buildings,including substances which are corrosive,explosive, flammable, radioactive or toxic.

Floor. Lower horizontal surface of any space ina building including finishes that are laid aspart of the permanent construction.

Groundwater. Water in liquid form, either as astatic water table or flowing through theground.

Interstitial condensation. Deposition of liquidwater from a vapour, occurring within orbetween the layers of the building envelope.

Moisture. Water in liquid, solid or gaseousform.

Precipitation. Moisture in any form falling fromthe atmosphere, usually as rain, sleet, snow orhail.

Roof. Any part of the external envelope of abuilding that is at an angle of less than 70° tothe horizontal.

Spray. Water droplets driven by the wind fromthe surface of the sea or other bodies of wateradjacent to buildings. Sea spray can beespecially hazardous to materials because ofits salt content.

Surface condensation. Deposition of liquidwater from a vapour, occurring on visiblesurfaces within the building.

Vapour control layer. Material of construction,usually a membrane, that substantially reducesthe water vapour transfer through any buildingin which it is incorporated.

Wall. Any opaque part of the external envelopeof a building that is at an angle of 70° or moreto the horizontal.


CGENERAL

13 Part IIA of the Environmental Protection Act 1990defines substance as “.. any natural or artificialsubstance, whether in solid or liquid form or in the formof gas or vapour.”

Site investigation1.1 The preparation of the site will depend onthe findings of the site investigation. The siteinvestigation is relevant to Sections 1, 2 and 3of this Approved Document and also to therequirements of Approved Document A withrespect to foundations. The site investigationshould consist of a number of well-definedstages:

a) Planning stage. Clear objectives shouldbe set for the investigation, including the scopeand requirements, which enable theinvestigation to be planned and carried outefficiently and provide the required information;

b) Desk study. A review of the historical,geological and environmental information aboutthe site is essential;

c) Site reconnaissance or walkoversurvey. This stage of the investigationfacilitates the identification of actual andpotential physical hazards and the design ofthe main investigation;

d) Main investigation and reporting. Thiswill usually include intrusive and non-intrusivesampling and testing to provide soil parametersfor design and construction. The maininvestigation should be preceded by b) and c)above.

1.2 The extent and level of investigationneeds to be tailored to the type of developmentand the previous use of land. Typically the siteinvestigation should include susceptibility togroundwater levels and flow, underlyinggeology, and ground and hydro-geologicalproperties. A geotechnical site investigationshould identify physical hazards for sitedevelopment, determine an appropriate design,and provide soil parameters for design andconstruction. British Standard BS 5930:199914

provides comprehensive guidance on siteinvestigations. Guidance on site investigationfor low-rise buildings is given in six BREDigests covering procurement15, desk studies16,the walk-over survey17, trial pits18, soildescription19 and direct investigation20.Reference should also be made to BS 8103-1:199521.

1.3 Where the site is potentially affected bycontaminants, a combined geotechnical andgeo-environmental investigation should beconsidered. Guidance on assessing andremediating sites affected by contaminants isgiven in Section 2: Resistance toContaminants.

Unsuitable material1.4 Vegetable matter such as turf and rootsshould be removed from the ground to becovered by the building at least to a depth toprevent later growth. The effects of roots closeto the building also need to be assessed.Consideration should be given to whether thisprovision need apply to a building used whollyfor:

a) storing goods, provided that any personswho are habitually employed in the building areengaged only in taking in, caring for, or takingout the goods; or

b) a purpose such that the provision wouldnot serve to increase protection to the healthor safety of any persons habitually employed inthe building.

1.5 Where mature trees are present on siteswith shrinkable clays (see Diagram 1 and Table1), the potential damage arising from groundheave to services and floor slabs and oversiteconcrete should be assessed. Referenceshould be made to BRE Digest 29822. Wheresoils and vegetation type would requiresignificant quantities of soil to be removed,reference should be made to BRE Digests 24123

and 24224, and to the FBE (Foundation for theBuilt Environment) report25. The effects ofremaining trees on services and buildingmovements close to the building need to be

Section 1: Clearance or treatment ofunsuitable material


C CLEARANCE OR TREATMENT OF UNSUITABLE MATERIAL

14 BS 5930:1999 Code of practice for site investigations15 BRE Digest 322 Site investigation for low-rise building:

procurement, 198716 BRE Digest 318 Site investigation for low-rise building:

desk studies, 198717 BRE Digest 348 Site investigation for low-rise building:

the walk-over survey, 198918 BRE Digest 381 Site investigation for low-rise building:

trial pits, 199319 BRE Digest 383 Site investigation for low-rise building:

soil description, 199320 BRE Digest 411 Site investigation for low-rise building:

direct investigations, 199521 BS 8103-1:1995 Structural design for low rise buildings22 BRE Digest 298 Low-rise building foundations: the

influence of trees in clay soils, 199923 BRE Digest 241 Low rise buildings on shrinkable clay

soils: Part 2, 199324 BRE Digest 242 Low rise buildings on shrinkable clay

soils: Part 3, 199325 Subsidence damage to domestic buildings: lessons

learned and questions remaining, FBE, 2000

assessed using guidance in NHBC (NationalHouse Building Council) Standards Chapter4.226.

1.6 Building services such as below-grounddrainage should be sufficiently robust orflexible to accommodate the presence of anytree roots. Joints should be made so that rootswill not penetrate them. Where roots couldpose a hazard to building services,consideration should be given to their removal.

1.7 On sites previously used for buildings,consideration should be given to the presenceof existing foundations, services, buried tanksand any other infra-structure that couldendanger persons in and about the buildingand any land associated with the building.

1.8 Where the site contains fill or madeground, consideration should be given to itscompressibility and its potential for collapse onwetting, and to appropriate remedial measuresto prevent damaging differential settlement.Guidance is given in BRE Digest 42727 and BREReport BR 42428.


CCLEARANCE OR TREATMENT OF UNSUITABLE MATERIAL

26 NHBC Standards Chapter 4.2 Building near trees,2003

27 BRE Digest 427 Low-rise buildings on fill28 BRE Report BR 424 Building fill: Geotechnical aspects,

2001

Clay type Volume change potential

Glacial Till Low

London High to very high

Oxford and Kimmeridge High

Lower Lias Medium

Gault High to very high

Weald High

Mercian mudstone Low to medium

Table 1 Volume change potential forsome common clays

Diagram 1 Distribution of shrinkable clays and principal sulfate/ sulfide bearingstrata in England and Wales

North of the indicated limit, much of thestrata are covered with glacial depositsthat are generally low in sulphate

Introduction2.1 A wide range of solid, liquid and gaseouscontaminants can arise on sites, especiallythose that have had a previous industrial use(see paragraph 0.12 for the definition of acontaminant). In particular, the burial ofbiodegradable waste in landfills can give rise tolandfill gas (see paragraph 2.25). Sites with agenerally rural use such as agriculture orforestry may be contaminated by pesticides,fertiliser, fuel and oils and decaying matter ofbiological origin.

2.2 Table 2 lists examples of sites that arelikely to contain contaminants. It is derivedfrom the “Industry Profile” guides produced bythe former Department of the Environment(DoE), each of which deals with a differentindustry with the potential to causecontamination29. Each profile identifiescontaminants which may be associated withthe industry, areas on the site in which theymay be found and possible routes formigration. The Department for the Environment,Food & Rural Affairs (Defra)/ EnvironmentAgency publication CLR 830 presents aselection of contaminants that may be relevantfor the assessment of land affected bycontaminants as they are likely to be found ona large number of industrial sites across theUK.

2.3 In addition, there can be problems ofnatural contaminants in certain parts of thecountry as a result of the underlying geology. Inthis instance the contaminants can be naturallyoccurring heavy metals (eg cadmium andarsenic) originating in mining areas, and gases(eg methane and carbon dioxide) originating incoal mining areas and from organic rich soilsand sediments such as peat and river silts. TheEnvironment Agency has produced twoguidance documents31,32 on this subject whichdiscuss the geographical extent of thesecontaminants, the associated hazards,methods of site investigation and protectivemeasures.

2.4 Natural contaminants also include theradioactive gas radon, although the specificapproach for assessing and managing the risksit poses is different to other contaminants (seeparagraphs 2.39 to 2.41).

2.5 Sulfate attack affecting concrete floorslabs and oversite concrete associated withparticular strata also needs to be considered.Principal areas of sulfate bearing strata inEngland and Wales are shown in Diagram 1and Table 1. BRE Special Digest SD133 providesguidance on investigation, concretespecification and design to mitigate the effectsof sulfate attack.

Section 2: Resistance to contaminants


C RESISTANCE TO CONTAMINANTS

Animal and animal products processing works

Asbestos works

Ceramics, cement and asphalt manufacturing works

Chemical works

Dockyards and dockland

Engineering works (including aircraft manufacturing, railwayengineering works, shipyards, electrical and electronicequipment manufacturing works)

Gas works, coal carbonisation plants and ancillary by-productworks

Industries making or using wood preservatives

Landfill and other waste disposal sites

Metal mines, smelters, foundries, steel works and metalfinishing works

Munitions production and testing sites

Oil storage and distribution sites

Paper and printing works

Power stations

Railway land, especially larger sidings and depots

Road vehicle fuelling, service and repair: garages and fillingstations

Scrap yards

Sewage works, sewage farms and sludge disposal sites

Tanneries

Textile works and dye works

Note: the above list is not exhaustive

Table 2 Examples of sites likely tocontain contaminants

29 Department of the Environment Industry Profiles, 199630 Defra/ Environment Agency Contaminated Land

Research Report CLR 8 Priority contaminants for theassessment of land, 2002

31 Environment Agency R & D Technical Report P291Information on land quality in England: Sources ofinformation (including background contaminants)

32 Environment Agency R & D Technical Report P292Information on land quality in Wales: Sources ofinformation (including background contaminants)

33 BRE Special Digest SD1 Concrete in aggressiveground, 2003

Solid and liquid contaminants

Risk assessment

General concepts

2.6 To ensure safe development of landaffected by contaminants the principles of riskassessment (as set out in paragraph 2.8 below)should be followed. The general approach isfounded on the concept of the “source-pathway-receptor” relationship, or pollutantlinkage, where source refers to contaminants inor on the ground. This is illustrated by theconceptual model34 in Diagram 2.

2.7 When land affected by contaminants isdeveloped, receptors (i.e. buildings, buildingmaterials and building services, as well aspeople) are introduced onto the site and so it isnecessary to break the pollutant linkages. Thiscan be achieved by:

a) treating the contaminant (eg use ofphysical, chemical or biological processes to eliminate or reduce thecontaminant’s toxicity or harmful properties);

b) blocking or removing the pathway (egisolating the contaminant beneath protective

layers or installing barriers to preventmigration);

c) protecting or removing the receptor (egchanging the form or layout of thedevelopment, using appropriately designedbuilding materials, etc.);

d) removing the contaminant (eg excavatingcontaminated material).


CRESISTANCE TO CONTAMINANTS

34 The conceptual model is a textual or schematichypothesis of the nature and sources of contamination,the pollution migration pathways and potentialreceptors, developed on the basis of the informationfrom a preliminary assessment, and is refined duringsubsequent phases of investigation.

Diagram 2 Example of a conceptual model for a site showing source-pathway-receptor

Stages of risk assessment

2.8 In assessing the risks for landcontamination a tiered approach is adoptedwith an increasing level of detail required inprogressing through the tiers. The three tiersare: preliminary risk assessment, genericquantitative risk assessment (GQRA) anddetailed quantitative risk assessment (DQRA).Once the need for a risk assessment has beenidentified, it will always be necessary toundertake a preliminary risk assessment, butdepending on the situation and the outcome, itmay not be appropriate to do a more detailedrisk assessment. Alternatively, it may benecessary to do only one or both of the moredetailed risk assessments. For each tier, theModel Procedures for the management of landcontamination (CLR 11, consultation draft2003), describes the stages of risk assessmentthat should be followed for identifying risks andmaking judgements about the consequences ofland affected by contamination whendeveloping a site. These are outlined below:

a) Hazard identification – developing theconceptual model by establishingcontaminant sources, pathways andreceptors. This is the preliminary siteassessment which consists of a desk study anda site walk-over in order to obtain sufficientinformation to obtain an initial understanding ofthe potential risks. An initial conceptual modelfor the site can be based on this information;

b) Hazard assessment – identifying whatpollutant linkages may be present andanalysing the potential for unacceptablerisks. Collect further information and undertakeexploratory site investigation to refineunderstanding of risks and the likelihood ofpollutant linkages. The results may beinterpreted using generic criteria andassumptions;

c) Risk estimation – establishing thescale of the possible consequences byconsidering the degree of harm that mayresult and to which receptors. Undertakedetailed ground investigation to collectsufficient data to estimate the risks thecontaminants may pose to defined receptorsunder defined conditions of exposure;

d) Risk evaluation – deciding whether therisks are acceptable or unacceptable.Review all site data to decide whetherestimated risks are unacceptable, taking intoaccount the nature and scale of anyuncertainties associated with the riskestimation process.

2.9 Guidance on the investigation of sitespotentially affected by contaminants isprovided in:

a) the Association of Geotechnical andGeoenvironmental Specialists (AGS)document35;

b) BS 5930:199936;

c) BS 10175:200137; and

d) the Environment Agencydocuments38,39,40,41,42,43,44,45.

They recommend a risk based approach toidentify and quantify the hazards that may bepresent and the nature of the risk they maypose. They describe the design and executionof field investigations, including suitablesample distribution strategies, sampling andtesting.

Hazard identification and assessment

2.10 A preliminary site assessment is requiredto provide information on the past and presentuses of the site and surrounding area that maygive rise to contamination (see Table 2). Duringthe site walk-over there may be signs ofpossible contaminants (see Table 3). Theinformation collated from the desk study and



35 Guidelines for combined geoenvironmental andgeotechnical investigations, Association ofGeotechnical and Geoenvironmental Specialists

36 BS 5930:1999 Code of practice for site investigations37 BS 10175:2001 Investigation of potentially

contaminated land. Code of practice38 National Groundwater & Contaminated Land Centre

report NC/99/38/2 Guide to good practice for thedevelopment of conceptual models and the selectionand application of mathematical models of contaminanttransport processes in the subsurface

39 Defra/ Environment Agency Contaminated LandResearch Report CLR 7 Assessment of risks to humanhealth from land contamination: an overview of thedevelopment of soil guideline values and relatedresearch, 2002

40 Defra/ Environment Agency Contaminated LandResearch Report CLR 8 Priority contaminants for theassessment of land, 2002

41 Defra/ Environment Agency Contaminated LandResearch Report CLR 9 Contaminants in soil: collationof toxicological data and intake values for humans,2002

42 Defra/ Environment Agency Contaminated LandResearch Report CLR 10 The contaminated landexposure assessment model (CLEA): technical basisand algorithms, 2002

43 Defra/ Environment Agency Contaminated LandResearch Report CLR 11 Handbook of modelprocedures for the management of contaminated land(in preparation)

44 Environment Agency R & D Technical Report P5-065Technical aspects of site investigation, 2000

45 Environment Agency R & D Technical Report P5-066Secondary model procedure for the development ofappropriate soil sampling strategies for landcontamination

site walkover can assist and will dictate thedesign of the exploratory and detailed groundinvestigation.

2.11 The site assessment and risk evaluationshould pay particular attention to the area ofthe site subject to building operations. Thoseparts of the land associated with the buildingthat include the building itself, gardens andother places on the site that are accessible tousers of the building and those in and aboutthe building should be remediated to therequirements of the Building Regulations.

There may be a case for a lower level ofremediation if part of, or the remainder of, theland associated with the building, or adjacentto such land, is accessible to a lesser extent tothe user or those in and about the buildingthan the main parts of the buildings and theirrespective gardens. This incremental approachmay also apply when very large sites aresubject to redevelopment in stages; it may bepossible to limit remediation to the site that issubject to building operations.

In all cases the risk evaluation and remediationstrategy documentation is likely to beappropriate for demonstrating that restrictedremediation is acceptable. The onus is on theapplicant to show why part of a site may beexcluded from particular remediation measures.

Even if the adjacent land is not subject toBuilding Regulations, which are concerned withhealth and safety, it may still be subject toplanning control legislation or to control underPart IIA of the Environmental Protection Act1990.

2.12 The Planning Authority should beinformed prior to any intrusive investigations orif any substance is found which is at variancewith any preliminary statements made aboutthe nature of the site.

Risk estimation and evaluation

2.13 The detailed ground investigation mustprovide sufficient information for theconfirmation of a conceptual model for the site,the risk assessment and the design andspecification of any remedial works. This islikely to involve collection and analysis of soil,soil gas, surface and groundwater samples bythe use of invasive and/ or non-invasivetechniques. An investigation of thegroundwater regime, levels and flows isessential for most sites since elevatedgroundwater levels could bring contaminantsclose to the surface both beneath the buildingand in any land associated with the building.Expert advice should be sought but furtherguidance and information are provided inAnnex A.

2.14 During the development of land affectedby contaminants the health and safety of boththe public and workers should beconsidered46,47.

Remedial measures

Introduction

2.15 If unacceptable risks to the definedreceptor have been identified then these needto be managed through appropriate remedialmeasures. The risk management objectives aredefined by the need to break the pollutantlinkages using the methods outlined inparagraph 2.6 and described below. Otherobjectives will also need to be considered suchas timescale, cost, remedial works, planningconstraints and sustainability. Depending onthe contaminant, three generic types ofremedial measures can be considered:treatment, containment and removal. Thecontainment or treatment of waste may require



Signs of possible Possible contaminantcontaminants

Vegetation Metals(absence, poor or Metal compoundsunnatural growth)

Organic compoundsGases (landfill or natural source)

Surface materials Metals(unusual colours and Metal compoundscontours may indicate

Oily and tarry wasteswastes and residues)

Asbestos

Other mineral fibres

Organic compounds including phenols

Combustible material including coal and coke dust

Refuse and waste

Fumes and odours Volatile organic and/or sulfurous (may indicate organic compounds from landfill or chemicals) petrol/solvent spillage

Corrosive liquids

Faecal animal and vegetable matter (biologically active)

Damage to exposed Sulfatesfoundations of existing buildings

Drums and containers Various(empty or full)

Note: the above list is not exhaustive

Table 3 Examples of possiblecontaminants

46 HSE Report HSG 66 Protection of workers and thegeneral public during the development of contaminatedland, 1991

47 CIRIA Report 132 A guide to safe working practices forcontaminated land, 1993

a waste management licence from theEnvironment Agency.

When building work is undertaken on sitesaffected by contaminants where controlmeasures are already in place, care must betaken not to compromise these measures. Forexample, cover systems may be breachedwhen new building foundations areconstructed, such as when extensions areadded.

Treatment

2.16 A wide range of treatment processes isnow available for dealing with contaminants.Biological, chemical and physical techniquescarried out either in or ex-situ exist which maydecrease one or more of the following featuresof the contaminants: mass, concentration,mobility, flux or toxicity. The choice of the mostappropriate technique for a particular site is ahighly site-specific decision for which specialistadvice should be sought.

Containment

2.17 Containment in its widest sense usuallymeans encapsulation of material containingcontaminants but in the context of buildingdevelopment containment is often taken tomean cover systems. However, in-groundvertical barriers may also be required to controllateral migration of contaminants.

2.18 Cover systems involve the placement ofone or more layers of materials over the site toachieve one or more of the followingobjectives:

a) break the pollutant linkage betweenreceptors and contaminants,

b) sustain vegetation,

c) improve geotechnical properties, and

d) reduce exposure to an acceptable level.

2.19 Some of the building structures, egfoundations, sub-structure and ground floor,may, dependent on the circumstances andconstruction, contribute to measures to provideeffective protection of health fromcontaminants.

2.20 Imported fill and soil for cover systemsshould be assessed at source to ensure that itis not contaminated above specifiedconcentrations and meets required standardsfor vegetation48. Design and dimensioning ofcover systems, particularly soil based onestypically used for gardens, should take accountof their long-term performance whereintermixing of the soil cover with thecontaminants in the ground can take place.Maintenance and monitoring may be necessary.Gradual intermixing due to natural effects andactivities such as burrowing animals,gardening, etc., needs to be considered.Excavations by householders for garden

features, etc., can penetrate the cover layerand may lead to exposure to contaminants.Further guidance on the design, constructionand performance of cover layers is given in theConstruction Industry Research andInformation Association (CIRIA) Report SP12449.

Removal

2.21 This involves the excavation and safedisposal to licensed landfill of the contaminantsand contaminated material. Excavation can betargeted to contaminant “hot spots”, or it maybe necessary to remove sufficient depth ofcontaminated material to accommodate a coversystem within the planned site levels. Removalmay not be viable depending on the extent anddepth of the contaminants on the site and theavailability of suitably licensed landfills.Imported fill should be assessed at source toensure that there are no materials that will poseunacceptable risks to potential receptors.

2.22 Further detailed guidance on all threetypes of remedial measure is given in theEnvironment Agency/ NHBC R & D Publication66 referred to above and in a series of CIRIApublications50,51,52,53,54,55.

Risks to buildings, building materials andservices

2.23 The hazards to buildings, buildingmaterials and services on sites affected bycontaminants need to be considered sincethese are also receptors. The hazards toconsider are:

a) Aggressive substances. These includeinorganic and organic acids, alkalis, organicsolvents and inorganic chemicals such assulfates and chlorides which may affect thelong-term durability of construction materials(such as concrete, metals and plastics);

b) Combustible fill. This includes domesticwaste, colliery spoil, coal, plastics, petrol-soaked ground, etc., which, if ignited, may lead



48 BS 3882:1994 Specification for topsoil49 CIRIA Special Publication SP124 Barriers, liners and

cover systems for containment and control of landcontamination, 1996

50 CIRIA Special Publication SP102 Decommissioning,decontamination and demolition, 1995

51 CIRIA Special Publication SP104 Classification andselection of remedial methods, 1995

52 CIRIA Special Publication SP105 Excavation anddisposal, 1995

53 CIRIA Special Publication SP106 Containment andhydraulic measures, 1996

54 CIRIA Special Publication SP107 Ex-situ remedialmethods for soils, sludges and sediments, 1995

55 CIRIA Special Publication SP109 In-situ methods ofremediation, 1995

to subterranean fires and consequent damageto structural stability of buildings, and theintegrity or performance of services;

c) Expansive slags. The two main types areblast furnace and steel making slag which mayexpand some time after deposition - usuallywhen water is introduced onto the site -causing damage to buildings and services;

d) Floodwater affected by contaminants.Substances in the ground, waste matter orsewage may contaminate floodwater. Thiscontaminated water may affect buildingelements, such as walls or ground floors, thatare close to or in the ground. Guidance onresistant construction can be found inPreparing for floods56 or Design guidance onflood damage to dwellings57.

2.24 Although the building and buildingmaterials are the main receptors with thesehazards, ultimately there could be harm tohealth. A particular concern is the effect ofhydrocarbons permeating potable water pipesmade of polyethylene. Guidance on reducingthese risks is given in a Water Research Centrereport58. Further guidance on the assessmentand management of risks to building materialsis given in an Environment Agency document59.

Methane and other gases from theground

Introduction

2.25 The term “methane and other gases” isused to define hazardous soil gases whichoriginate either from waste deposited in landfillsites or are generated naturally. It does notinclude radon which is dealt with separately inparagraphs 2.39 to 2.41. However, the termdoes include volatile organic compounds(VOCs). As stated in Limitations onRequirements above, measures described inthis document are the minimum that areneeded to comply with the BuildingRegulations. Further actions may be necessaryto deal with the requirements of otherlegislation.

2.26 Landfill gas is generated by the action ofmicro-organisms on biodegradable wastematerials in landfill sites. It generally consistsof methane and carbon dioxide together withsmall quantities of VOCs which give the gas itscharacteristic odour. Methane and oxygendeficient atmospheres (sometimes referred toas stythe or black-damp) containing elevatedlevels of carbon dioxide and nitrogen can begenerated naturally in coal mining areas.Methane and carbon dioxide can also beproduced by organic rich soils and sedimentssuch as peat and river silts. A wide range ofVOCs can also be present as a result of petrol,oil and solvent spillages. Methane and othergases can migrate through the subsoil andthrough cracks and fissures into buildings.

2.27 Methane is an explosive and asphyxiatinggas. Carbon dioxide although non-flammable istoxic. VOCs are not only flammable and toxicbut can also have a strong, unpleasant odour.Should any of these gases build up tohazardous levels in buildings then they cancause harm to health or compromise safety.

Risk assessment2.28 The risk assessment process outlined inparagraph 2.8 should also be adopted formethane and other gases. Further investigationfor hazardous soil gases may be requiredwhere the ground to be covered by the buildingand/ or any land associated with the buildingis:

a) On a landfill site, within 250m of theboundary of a landfill site or where there issuspicion that it is within the sphere ofinfluence of such a site. The EnvironmentAgency’s policy on building development on ornear to landfills should be followed;

b) On a site subject to the wide scaledeposition of biodegradable substances(including made ground or fill);

c) On a site that has been subject to a usethat could give rise to petrol, oil or solventspillages;

d) In an area subject to naturally occurringmethane, carbon dioxide and other hazardousgases (eg hydrogen sulfide).

2.29 There are documents that coverhazardous soil gases in these specificcontexts:

a) Waste Management Paper No 2760 givesguidance on the generation and movement oflandfill gas as well as techniques for itsinvestigation. Complementary guidance is givenin a document61 by the Chartered Institution ofWastes Management (CIWM);



56 Preparing for floods: interim guidance for improving theflood resistance of domestic and small businessproperties, DTLR, 2002

57 BRE for Scottish Office Design guidance on flooddamage for dwellings, TSO, 1996

58 Foundation for Water Research report FR0448 Layingpotable water pipelines in contaminated ground:guidance notes, 1994

59 Assessment and management of risks to buildings,building materials and services from landcontamination, Environment Agency, 2001

60 HMIP Waste Management Paper No 27 The control oflandfill gas, TSO, 2nd edition 1991

61 Monitoring of landfill gas, Chartered Institution ofWastes Management (CIWM), 2nd edition 1998

b) The Institute of Petroleum has prepared aguidance document covering petroleum retailsites62;

c) The BGS report on naturally occurringmethane and other gases63 gives guidance onthe geographical extent of these contaminants,the associated hazards and methods of siteinvestigation. This is supported by a reportsponsored by the former DoE on methane andother gases in disused coal mining areas64;

d) In addition, CIRIA has produced threerelevant guidance documents on methane andother gases which describe how such gasesare generated and move within the ground65,methods of detection and monitoring66 andinvestigation strategies67.

2.30 During a site investigation for methaneand other gases it is important to takemeasurements over a sufficiently long period oftime in order to characterise gas emissionsfully. This should also include periods when gasemissions are likely to be higher, eg duringperiods of falling atmospheric pressure. It isalso important to establish not only theconcentration of these gases in the ground butalso the quantity of gas generating materials,their rate of gas generation, gas movement inthe ground and gas emissions from the groundsurface. This is an important part of the riskestimation stage. Indications about the gasregime in the ground can be obtained throughsurface emission rate and borehole flow ratemeasurements, and guidance on this is given inCIRIA Reports 15168 and 15269.

2.31 Construction activities undertaken as partof building development can alter the gasregime on the site. For example, a site stripcan increase surface gas emissions as canpiling and excavation for foundations, anddynamic compaction can push drybiodegradable waste into moist, gas-activezones.

2.32 There are no Soil Guideline Values (seeAnnex A) for methane and other gases. Whenassessing gas risks in the context of traditionalhousing there is a need to consider twopathways for human receptors: (i) gas enteringthe dwelling through the substructure, andbuilding up to hazardous levels, and (ii)subsequent householder exposure in gardenareas which can include where outbuildings (eggarden sheds and greenhouses) and extensionsare constructed, and where there may also beexcavations for garden features (eg ponds).

2.33 Guidance on undertaking gas riskassessment is given in CIRIA Report 15269, andthe GaSIM model is also available forassessing gas emissions from landfill sites70.There is further discussion of gas riskassessment in the forthcoming Defra/Environment Agency document CLR 1171.

2.34 CIRIA Report 14972 and the Department ofthe Environment, Transport and the Regions

(DETR) Partners in Technology (PIT) report73

describe a range of ground gas regimes(defined in terms of soil gas concentrations ofmethane and carbon dioxide as well asborehole flow rate measurements) which canbe helpful in assessing gas risks.

2.35 Depending on the proposed use, for non-domestic development the focus might be onthe building only, but the general approach isthe same.

Remedial measures

2.36 If the risks posed by the gas areunacceptable then these need to be managedthrough appropriate building remedialmeasures. Site-wide gas control measures maybe required if the risks on any land associatedwith the building are deemed unacceptable.Such control measures include removal of thegas generating material or covering togetherwith gas extraction systems. Further guidanceis contained in CIRIA Report 14972. Generallyspeaking, expert advice should be sought inthese circumstances.

2.37 Gas control measures for dwellingsconsist of a gas resistant barrier across thewhole footprint (i.e. walls and floor) above anextraction (or ventilation) layer from whichgases can be dispersed and vented toatmosphere. They are normally passive, i.e. gasflow is driven by stack (temperature difference)and wind effects. Consideration should be



62 Institute of Petroleum TP 95 Guidelines for investigationand remediation of petroleum retail sites, 1998

63 BGS Technical Report WP/95/1 Methane, carbondioxide and oil seeps from natural sources and miningareas: characteristics, extent and relevance to planningand development in Great Britain, 1995

64 Methane and other gases from disused coal mines: theplanning response, TSO, 1996

65 CIRIA Report 130 Methane: its occurrence andhazards in construction, 1993

66 CIRIA Report 131 The measurement of methane andother gases from the ground, 1993

67 CIRIA Report 150 Methane investigation strategies,1995

68 CIRIA Report 151 Interpreting measurements of gas inthe ground, 1995

69 CIRIA Report 152 Risk assessment for methane andother gases from the ground, 1995

70 Environment Agency GasSIM - Landfill gas assessmenttool.

71 Defra/ Environment Agency Contaminated LandResearch Report CLR 11 Handbook of modelprocedures for the management of contaminated land(in preparation)

72 CIRIA Report 149 Protecting development frommethane, 1995

73 DETR/ Arup Environmental PIT Research Report:Passive venting of soil gases beneath buildings, 1997

given to the design and layout of buildings tomaximise the driving forces of naturalventilation. Further guidance on this anddetailed practical guidance on the constructionof protective measures for housing is given inthe BRE/ Environment Agency report BR 41474.(In order to accommodate gas resistantmembrane, for example as shown in BR414,the position and type of insulation may have tobe adjusted). The DETR/ Arup Environmentalreport73 compares the performance of a rangeof commonly used gas control measures andcan be used as a guide to the design of suchmeasures.

2.38 Gas control measures for non-domesticbuildings use the same principles as thoseused for housing, and the DETR/ ArupEnvironmental report can also be used as aguide to design. Expert advice should besought as the floor area of such buildings canbe large and it is important to ensure that gasis adequately dispersed from beneath the floor.The use of mechanical (as opposed to passive)systems and monitoring and alarm systemsmay be necessary. There is a need forcontinued maintenance and calibration of thesesystems, so they are more appropriate withnon-domestic buildings (as opposed todwellings) since there is usually scope for this.Again, expert advice should be sought. Specialsub-floor ventilation systems are carefullydesigned to ensure adequate performance andshould not be modified unless subjected to aspecialist review of the design. Such ventilationsystems, particularly those using poweredventilation, are unlikely to be appropriate forowner occupied properties as there is a risk ofinterference by users.

Radon2.39 Radon is a naturally occurring radioactivecolourless and odourless gas which is formedin small quantities by radioactive decaywherever uranium and radium are found. It canmove through the subsoil and so into buildings.Some parts of the country, notably the WestCountry, have higher levels than elsewhere.Exposure to high levels for long periodsincreases the risk of developing lung cancer. Toreduce this risk all new buildings, extensionsand conversions, whether residential or non-domestic, built in areas where there may beelevated radon emissions, may need toincorporate precautions against radon.

2.40 Guidance on the areas susceptible toradon and practical protective measures hasbeen published by the BRE as a Report BR21175. This guidance was developed to showradon protective measures for dwellings.

A European Council Directive establishes acommon basis for radiation protectionlegislation in all Member States. The IonisingRadiations Regulations76 sets a nationalreference level for radon gas and employers

and self-employed persons responsible for aworkplace are required to measure radon levelson being directed to do so. See also HSE/BREguide to Radon in the Workplace77.

There is at present no guidance on protectionfrom radon in the workplace but some of thetechniques used for installing a radon resistantmembrane, described in BR 211, may besuitable for use in domestic sized buildingswith heating and ventilation regimes similar tothose used in dwellings. The guidance in BR211 can be used as the basis for radonprotection of other building types but thisshould be done with caution. Information inRadon in the Workplace provides guidance forexisting non-domestic buildings.

Interim guidance on extensions can be found inGBG 25 Buildings and Radon78.

2.41 Although the precise areas wheremeasures should be taken are listed in the BREReport, these are reviewed by ODPM (Office ofthe Deputy Prime Minister) in the light of advicefrom the National Radiological Protection Board(NRPB) and the British Geological Survey(BGS). Current information on the areasdelineated by ODPM for the purposes ofBuilding Regulations should be obtained fromlocal authority building control officers or fromapproved inspectors. Changes to areasdelineated as requiring radon protection will benotified to Building Control Bodies and will beposted on the ODPM website.



74 BRE/ Environment Agency Report BR 414 Protectivemeasures for housing on gas-contaminated land, 2001

75 BRE Report BR 211 Radon: guidance on protectivemeasures for new dwellings, 1999.

76 The Ionising Radiations Regulations 1999 (SI1999/3232).

77 BRE Report BR 293 Radon in the workplace, 199578 BRE GBG 25 Buildings and radon, 1996

3.1 The provisions which follow assume thatthe site of the building is not subject to generalflooding (see paragraph 0.8) or, if it is, thatappropriate steps are being taken.

3.2 Where the water table can rise to within0.25m of the lowest floor of the building, orwhere surface water could enter or adverselyaffect the building, either the ground to becovered by the building should be drained bygravity, or other effective means ofsafeguarding the building should be taken.

3.3 If an active sub-soil drain is cut duringexcavation and if it passes under the building itshould be:

a) re-laid in pipes with sealed joints andhave access points outside the building; or

b) re-routed around the building, or

c) re-run to another outfall (see Diagram 3).

3.4 Where there is a risk that groundwaterbeneath or around the building could adverselyaffect the stability and properties of theground, consideration should be given to sitedrainage or other protection (see Section 4:Floors).

3.5 For protecting low lying buildings orbasements from localised flooding where foulwater drainage also receives rainwater, refer toApproved Document H (Drainage and wastedisposal). In heavy rainfall these systemssurcharge and where preventative measures arenot taken this could lead to increased risks offlooding within the property.

3.6 Flooding can create blockages in drainsand sewers that can lead to backflow ofsewage into properties through low level draingullies, toilets, etc. Guidance on anti-floodingdevices is given in a CIRIA publication79.

3.7 General excavation work for foundationsand services can alter groundwater flowsthrough the site. Where contaminants arepresent in the ground, consideration should begiven to subsoil drainage to prevent thetransportation of water-borne contaminants tothe foundations or into the building or itsservices.

Section 3: Sub-soil drainage


C SUB-SOIL DRAINAGE

79 CIRIA Publication C506 Low-cost options forprevention of flooding from sewers, 1998


CSUB-SOIL DRAINAGE

Diagram 3 Subsoil drain cut during excavation

4.1 This Section gives guidance for fivesituations:

a) ground supported floors exposed tomoisture from the ground (see paragraphs 4.6to 4.12);

b) suspended timber ground floors exposedto moisture from the ground (see paragraphs4.13 to 4.16);

c) suspended concrete ground floorsexposed to moisture from the ground (seeparagraphs 4.17 to 4.20);

d) the risk of interstitial condensation inground floors and floors exposed from below(see paragraph 4.21);

e) the risk of surface condensation andmould growth on any type of floor (seeparagraph 4.22).

4.2 Floors next to the ground should:

a) resist the passage of ground moisture tothe upper surface of the floor;

b) not be damaged by moisture from theground;

c) not be damaged by groundwater;

d) resist the passage of ground gases. Tomeet requirement C1 (2) floors in somelocalities may need to resist the passage ofhazardous ground gases such as radon ormethane. Remedial measures which will includea gas resistant barrier which, with properdetailing, can function also as a damp proofmembrane. For specific guidance for methaneand other gases refer to paragraphs 2.25 to2.38, and for radon refer to paragraphs 2.39 to2.41. Guidance is provided in reports BR 41480

and BR 21181 respectively.

4.3 Consideration should be given to whether4.2a) need apply to a building used wholly for:



4.4 Floors next to the ground and floorsexposed from below should be designed andconstructed so that their structural and thermalperformance are not adversely affected byinterstitial condensation.

4.5 All floors should not promote surfacecondensation or mould growth, givenreasonable occupancy conditions.

Ground supported floors (moisturefrom the ground)4.6 Any ground supported floor will meet therequirement if the ground is covered withdense concrete laid on a hardcore bed and adamp-proof membrane is provided. Suitableinsulation may be incorporated.

Technical solution

4.7 Unless it is subjected to water pressure,which is likely in the case of buildings on verypermeable strata such as chalk, limestone orgravel (in which case see Alternative approach,paragraph 4.12), a concrete ground supportedfloor may be built as follows (Diagram 4):

a) well compacted hardcore bed, no greaterthan 600mm deep82, of clean, broken brick orsimilar inert material, free from materialsincluding water-soluble sulfates in quantitieswhich could damage the concrete (BRE Digest27683; and

b) concrete at least 100mm thick (butthicker if the structural design requires) to mixST2 in BS 8500 or, if there is embeddedreinforcement, to mix ST4 in BS 850084; and

c) damp-proof membrane above or belowthe concrete, and continuous with the damp-proof courses in walls, piers and the like. If theground could contain water soluble sulfates, orthere is any risk that sulfate or otherdeleterious matter could contaminate thehardcore; the membrane should be placed atthe base of the concrete slab85.

Section 4: Floors


C FLOORS

80 BRE/ Environment Agency Report BR 414 Protectivemeasures for housing on gas-contaminated land, 2001

81 BRE Report BR 211 Radon: guidance on protectivemeasures for new dwellings, 1999

82 If the hardcore bed is deeper than 600mm, there maybe a risk of excessive settlement and cracking of thefloor slab. In such cases, a suspended floor slab isadvised

83 BRE Digest 276 Hardcore, 199284 BS 8500-1: 2002 Concrete. Complementary British

Standard to BS EN 206-1. Method of specifying andguidance for the specifier

85 BRE Special Digest SD1 Concrete in aggressiveground, 2003

4.8 A membrane below the concrete could beformed with a sheet of polyethylene, whichshould be at least 300mm thick (1200 gauge)with sealed joints and laid on a bed of materialthat will not damage the sheet.

4.9 A membrane laid above the concrete maybe either polyethylene sheet as describedabove (but without the bedding material) orthree coats of cold applied bitumen solution orsimilar moisture and water vapour resistingmaterial. In each case it should be protectedeither by a screed or a floor finish, unless themembrane is pitchmastic or similar materialwhich will also serve as a floor finish.

4.10 Insulants placed beneath floor slabsshould have sufficient strength to resist theweight of the slab, the anticipated floor loadingas well as any possible overloading duringconstruction. In order to resist degradationinsulation that is placed below the damp proofmembrane should have low water absorption. Ifnecessary the insulant should be resistant tocontaminants in the ground.

4.11 A timber floor finish laid directly onconcrete may be bedded in a material whichmay also serve as a damp-proof membrane.Timber fillets laid in the concrete as a fixing fora floor finish should be treated with an effectivepreservative unless they are above the damp-proof membrane. Some preservative treatmentsare described in BS 1282:199986.

Alternative approach

4.12 The requirement can also be achieved byfollowing the relevant recommendations ofClause 11 of BS CP 102:197387. BS 8102:199088

includes recommendations for floors subject towater pressure.

Suspended timber ground floors(moisture from the ground)4.13 Any suspended timber floor next to theground will meet the requirement if:

a) the ground is covered so as to resistmoisture and prevent plant growth; and

b) there is a ventilated air space betweenthe ground covering and the timber; and

c) there are damp-proof courses betweenthe timber and any material which can carrymoisture from the ground.


CFLOORS

Diagram 4 Ground supported floor - construction (see paragraph 4.7)

86 BS 1282:1999 Wood preservatives. Guidance onchoice, use and application

87 BS CP 102:1973 Protection of buildings against waterfrom the ground

88 BS 8102:1990 Code of practice for protection ofstructures against water from the ground

Technical solution

4.14 Unless it is covered with a floor finishwhich is highly vapour resistant (in which casesee the Alternative approach in paragraph4.16), a suspended timber floor next to theground may be built as follows (Diagram 5):

a) Ground covering either:

(i) unreinforced concrete at least 100mmthick to mix ST 1 in BS 850089. Theconcrete should be laid on a hardcorebed of clean, broken brick or any otherinert material free from materialsincluding water-soluble sulfates inquantities which could damage theconcrete; or

(ii) concrete, composed as describedabove, or inert fine aggregate, in eithercase at least 50mm thick laid on atleast 300µm (1200 gauge) polyethylene

sheet with sealed joints, and itself laidon a bed of material which will notdamage the sheet.

To prevent water collecting on the groundcovering, either the top should be entirely abovethe highest level of the adjoining ground or, onsloping sites, consideration should be given toinstalling drainage on the outside of the up-slope side of the building (see Diagram 6);

b) Ventilated air space measuring at least75mm from the ground covering to theunderside of any wall plates and at least150mm to the underside of the suspendedtimber floor (or insulation if provided). Twoopposing external walls should have ventilationopenings placed so that the ventilating air willhave a free path between opposite sides and toall parts. The openings should be not less thaneither 1500 mm2/m run of external wall or 500mm2/m2 of floor area, whichever gives the


C FLOORS

Diagram 5 Suspended timber floor - construction (see paragraph 4.14 a) (i))

Diagram 6 Suspended floor - preventing water collection (see paragraph 4.14a)

89 BS 8500-1: 2002 Concrete. Complementary BritishStandard to BS EN 206-1. Method of specifying andguidance for the specifier

greater opening area. Any pipes needed tocarry ventilating air should have a diameter ofat least 100mm. Ventilation openings shouldincorporate suitable grilles which prevent theentry of vermin to the subfloor but do not resistthe air flow unduly. If floor levels need to benearer to the ground to provide level accesssub-floor ventilation can be provided throughoffset (periscope) ventilators;

c) Damp-proof courses of impervious sheetmaterial, engineering brick or slates in cementmortar or other material which will prevent thepassage of moisture. Guidance for choice ofmaterials is given in BS5628: Part3: 200190;

d) In shrinkable clay soils, the depth of theair space may need to be increased to allow forheave.

4.15 In areas such as kitchens, utility roomsand bathrooms where water may be spilled,any board used as a flooring, irrespective ofthe storey, should be moisture resistant. In thecase of chipboard it should be of one of thegrades with improved moisture resistancespecified in BS 7331:199091 or BS EN 312 Part5:199792. It should be laid, fixed and jointed inthe manner recommended by the manufacturer.To demonstrate compliance the identificationmarks should be facing upwards. Any softwoodboarding should be at least 20mm thick andfrom a durable species93 or treated with asuitable preservative.


4.16 The requirement can also be met (seeparagraph 4.14 above) by following the relevantrecommendations of Clause 11 of BS CP102:197394.

Suspended concrete groundfloors (moisture from the ground)4.17 Any suspended floor of in-situ or precastconcrete, including beam and block floors, nextto the ground will meet the requirement if it willadequately prevent the passage of moisture tothe upper surface and if the reinforcement isprotected against moisture.

Technical solution

4.18 One solution for a suspended concretefloor could be:

a) in-situ concrete at least 100mm thick (butthicker if the structural design requires)containing at least 300kg of cement for eachm3 of concrete; or

b) precast concrete construction with orwithout infilling slabs; and

c) reinforcing steel protected by concretecover of at least 40mm if the concrete is in-situand at least the thickness required for amoderate exposure if the concrete is precast.

4.19 A suspended concrete floor will meet therequirements if it incorporates:

a) a damp-proof membrane (if the groundbelow the floor has been excavated below thelowest level of the surrounding ground and willnot be effectively drained); and

b) a ventilated air space. This shouldmeasure at least 150mm clear from the groundto the underside of the floor (or insulation ifprovided). Two opposing external walls shouldhave ventilation openings placed so that theventilating air will have a free path betweenopposite sides and to all parts of the floor void.The openings should be not less than either1500mm2/m run of external wall or 500mm2/m2

of floor area, whichever gives the greateropening area. Any pipes needed to carryventilating air should have a diameter of atleast 100mm. Ventilation openings shouldincorporate suitable grilles which prevent theentry of vermin to the subfloor but do not resistthe air flow unduly.

4.20 In localities where flooding is likely,consideration may be given to including meansof inspecting and clearing out the sub-floorvoids beneath suspended floors. For guidance,see the DTLR publication on preparing forfloods95.


CFLOORS

90 BS 5628-3:2001 Code of practice for use of masonry.Materials and components, design and workmanship

91 BS 7331:1990 Specification for direct surfaced woodchipboard based on thermosetting resins

92 BS EN 312-5:1997 Particleboards. Specifications.Requirements for load-bearing boards for use in humidconditions

93 BRE Digest 429 Timbers and their natural durabilityand resistance to preservative treatment, 1998

94 BS CP 102:1973 Protection of buildings against waterfrom the ground

95 Preparing for floods: interim guidance for improving theflood resistance of domestic and small businessproperties, DTLR, 2002 (Available from ODPM)

Ground floors and floors exposedfrom below (resistance to damagefrom interstitial condensation)4.21 A ground floor or floor exposed frombelow, i.e. above an open parking space orpassageway, as shown in Diagram 7, will meetthe requirement if it is designed andconstructed in accordance with Clause 8.5 andAppendix D of BS 5250:200296, BS EN ISO13788:200197 and BR 26298.

Floors (resistance to surfacecondensation and mould growth)4.22 A floor will meet the requirement if:

a) a ground floor is designed andconstructed so that the thermal transmittance(U-value) does not exceed 0.7 W/m2K at anypoint; and

b) in the case of all floors, the junctionsbetween elements are designed in accordancewith the recommendations in the report99 onrobust construction details, or follow theguidance of BRE IP17/01100.


C FLOORS

Diagram 7 Typical floors exposed from below

96 BS 5250:2002 Code of practice for the control ofcondensation in buildings

97 BS EN ISO 13788:2001 Hygrothermal performance ofbuilding components and building elements. Internalsurface temperature to avoid critical surface humidityand interstitial condensation. Calculation methods

98 BRE Report BR 262 Thermal insulation: avoiding risks,2002

99 Limiting thermal bridging and air leakage: robustconstruction details for dwellings and similar buildings,TSO, 2001

100 BRE Information Paper IP17/01 Assessing the effectsof thermal bridging at junctions and around openings,2001

5.1 This section gives guidance for foursituations:

a) internal and external walls exposed tomoisture from the ground (see paragraphs 5.4to 5.6);

b) external walls exposed to precipitationfrom the outside, covering:

i) solid external walls (see paragraphs5.8 to 5.11);

ii) cavity external walls (see paragraphs5.12 to 5.15);

iii) framed external walls (see paragraph5.17);

iv) cracking of walls (see paragraph 5.18);

v) impervious cladding systems (seeparagraphs 5.19 to 5.28);

vi) the joint between window and doorframes and external walls and doorthresholds (see paragraphs 5.29 to5.33);

c) the risk of interstitial condensation in anytype of wall (see paragraphs 5.34 to 5.35);

d) the risk of surface condensation or mouldgrowth on any type of wall (see paragraph5.36).

A wall includes piers, columns and parapets. Italso includes chimneys if they are attached tothe building. It does not include windows,doors and similar openings, but does includethe joint between their frames and the wall. Inthe following, the term ‘precipitation’ includesthe effects of spray blown from the sea or anyother body of water adjacent to the building

5.2 Walls should:

a) resist the passage of moisture from theground to the inside of the building; and

b) not be damaged by moisture from theground and not carry moisture from the groundto any part which would be damaged by it,

and, if the wall is an external wall:

c) resist the penetration of precipitation tocomponents of the structure that might bedamaged by moisture; and

d) resist the penetration of precipitation tothe inside of the building; and

e) be designed and constructed so thattheir structural and thermal performance arenot adversely affected by interstitialcondensation; and

f) not promote surface condensation ormould growth, given reasonable occupancyconditions.

5.3 Consideration should be given to whetherprovisions 5.2a) and d) need apply to a buildingused wholly for:



Internal and external walls(moisture from the ground)5.4 Any internal or external wall will meet therequirement if a damp proof course is provided.

Technical solution

5.5 An internal or external wall will meet therequirement if it is built as follows (unless it issubject to groundwater pressure, in which casesee the Alternative approach - paragraph 5.6):

a) damp-proof course of bituminousmaterial, polyethylene, engineering bricks orslates in cement mortar or any other materialthat will prevent the passage of moisture. Thedamp proof course should be continuous withany damp-proof membrane in the floors; and

b) if the wall is an external wall, the damp-proof course should be at least 150mm abovethe level of the adjoining ground (see Diagram8), unless the design is such that a part of thebuilding will protect the wall; and

c) if the wall is an external cavity wall, (seeDiagram 9a) the cavity should be taken downat least 225mm below the level of the lowestdamp-proof course, or a damp-proof trayshould be provided so as to preventprecipitation passing into the inner leaf (seeDiagram 9b), with weep holes every 900mm toassist in the transfer of moisture through theexternal leaf. Where the damp-proof tray doesnot extend the full length of the exposed wall,i.e. above an opening, stop ends and at leasttwo weep holes should be provided.


5.6 The requirement can also be met byfollowing the relevant recommendations ofClauses 4 and 5 of BS 8215:1991101. BS8102:1990102 includes recommendations for

Section 5: Walls


CWALLS

101 BS 8215:1991 Code of practice for design andinstallation of damp-proof courses in masonryconstruction

102 BS 8102:1990 Code of practice for protection ofstructures against water from the ground


C WALLS

Diagram 8 Damp proof courses (see paragraph 5.5b)

Diagram 9 Protecting inner leaf (see paragraph 5.5c)

walls subject to groundwater pressure includingbasement walls.

External walls (moisture from theoutside)5.7 As well as giving protection againstmoisture from the ground, an external wallshould give protection against precipitation.This protection can be given by a solid wall ofsufficient thickness (see paragraphs 5.8 to5.11), or by a cavity wall (see paragraphs 5.12to 5.18), or by an impervious or weather-resisting cladding (see paragraphs 5.19 to5.28).

Solid external walls5.8 Any solid wall will meet the requirement ifit will hold moisture arising from rain and snowuntil it can be released in a dry period withoutpenetrating to the inside of the building, orcausing damage to the building. The wallthickness will depend on the type of brick andblock and on the severity to wind driven rain. Amethod of describing the exposure to wind-driven rain is given in BS 8104:1992103; see alsoBS 5628-3:2001104.

Technical solution

5.9 A solid external wall in conditions of verysevere exposure should be protected byexternal impervious cladding, but in conditionsof severe exposure may be built as follows:

a) brickwork or stonework at least 328mmthick, dense aggregate concrete blockwork atleast 250mm thick, or lightweight aggregate oraerated autoclaved concrete blockwork atleast 215mm thick; and

b) rendering: the exposed face of the bricksor blocks should be rendered or be given noless protection. Rendering should be in twocoats with a total thickness of at least 20mmand should have a scraped or textured finish.The strength of the mortar should becompatible with the strength of the bricks orblocks. The joints, if the wall is to be rendered,should be raked out to a depth of at least10mm. Further guidance is given in BS EN998:2002105. The rendering mix should be 1 partof cement, 1 part of lime and 6 parts of wellgraded sharp sand (nominal mix 1:1:6) unlessthe blocks are of dense concrete aggregate, inwhich case the mix may be 1:1⁄2:4. BS5262:1991106 includes recommendations for awider range of mixes according to the severityof exposure and the type of brick or block.

Premixed and proprietary renders should beused in accordance with manufacturer'sinstructions;

c) protection should be provided where thetop of walls, etc., would otherwise beunprotected (see Diagram 10). Unless theprotection and joints will be a complete barrier

to moisture, a damp proof course should alsobe provided;

d) Damp-proof courses, cavity trays andclosers should be provided and designed toensure that water drains outwards:

(i) where the downward flow will beinterrupted by an obstruction, such assome types of lintel; and

(ii) under openings, unless there is a silland the sill and its joints will form acomplete barrier; and

(iii)at abutments between walls and roofs.

5.10 Insulation. A solid external wall may beinsulated on the inside or on the outside.Where it is on the inside a cavity should beprovided to give a break in the path formoisture and where it is on the outside itshould provide some resistance to the ingressof moisture to ensure the wall remains relativelydry (see Diagram 11).


CWALLS

Diagram 10 Protection of wall headfrom precipitation (seeparagraph 5.9c)

103 BS 8104:1992 Code of practice for assessingexposure of walls to wind-driven rain


105 BS EN 998-2:2002 Specification of mortar for masonry106 BS 5262:1991 Code of practice for external renderings


5.11 The requirement can also be met byfollowing the relevant recommendations of BS 5628-3:2001107. The code describesalternative constructions to suit the severity ofthe exposure and the type of brick or block.

Cavity external walls5.12 Any external cavity wall will meet therequirement if the outer leaf is separated fromthe inner leaf by a drained air space, or in anyother way which will prevent precipitation frombeing carried to the inner leaf.

Technical solution

5.13 The construction of a cavity external wallcould include:

a) outer leaf masonry (bricks, blocks, stoneor manufactured stone); and

b) cavity at least 50mm wide. The cavity isto be bridged only by wall ties, cavity traysprovided to prevent moisture being carried tothe inner leaf (see paragraph 5.15 for cavityinsulation), and cavity barriers, firestops andcavity closures, where appropriate; and

c) inner leaf masonry or frame with lining.

Masonry units should be laid on a full bed ofmortar with the cross joints substantially andcontinuously filled to ensure structuralrobustness and weather resistance.

Where a cavity is to be partially filled, theresidual cavity should not be less than 50mmwide (see Diagram 11).


5.14 The requirement can also be met byfollowing the relevant recommendations of BS5628-3:2001108. The code describes factorsaffecting rain penetration of cavity walls.

Cavity insulation 5.15 A full or partial fill insulating material maybe placed in the cavity between the outer leafand an inner leaf of masonry subject to thefollowing conditions:

a) The suitability of a wall for installinginsulation into the cavity should be determinedeither by reference to the map in Diagram 12and the associated Table 4 or following thecalculation or assessment procedure in currentBritish or CEN standards. When partial fillmaterials are to be used, the residual cavityshould not be less than 50mm nominal; and

b) A rigid (board or batt) thermal insulatingmaterial built into the wall should be thesubject of current certification from anappropriate body or a European TechnicalApproval and the work should be carried out inaccordance with the requirements of thatdocument; or

c) Other insulating materials inserted intothe cavity after the wall has been constructedshould have certification from an appropriatebody and be installed in accordance with theappropriate installations code. The suitability ofthe wall for filling is to be assessed before thework is carried out and the person undertakingthe work should operate under an ApprovedInstaller Scheme that includes an assessmentof capability. Alternatively the insulatingmaterial should be the subject of currentcertification from an appropriate body or aEuropean Technical Approval and the workshould be carried out in accordance with therequirements of that document by operativeseither directly employed by the holder of thedocument or employed by an installerapproved to operate under the document; or

d) Urea-formaldehyde foam inserted into thecavity should be in accordance with BS5617:1985109 and be installed in accordancewith BS 5618:1985110. The suitability of the wallfor foam filling is to be assessed before thework is carried out and the person undertakingthe work should operate under an ApprovedInstaller Scheme that includes an assessmentof capability;

e) When the cavity of an existing house isbeing filled, special attention should be givento the condition of the external leaf of the wall,eg its state of repair and type of pointing.Guidance is given in BS 8208, Part 1:1985111.Some materials that are used to fill existingcavity walls may have a low risk of moisturebeing carried over to the internal leaf of thewall. In cases where a third party assessmentof such a cavity fill material contains a methodof assessing the construction of the walls andexposure risk, the procedure set out below maybe replaced by that method.


C WALLS



109 BS 5617:1985 Specification for urea-formaldehyde (UF)foam systems suitable for thermal insulation of cavitywalls with masonry or concrete inner and outer leaves

110 BS 5618:1985 Code of practice for thermal insulationof cavity walls (with masonry or concrete inner andouter leaves) by filling with urea-formaldehyde (UF)foam systems

111 BS 8208, Part 1:1985 Guide to assessment ofsuitability of external cavity walls for filling with thermalinsulation


CWALLS

Diagram 11 Insulated external walls: examples (see paragraphs 5.10 and 5.13)


C WALLS

Diagram 12 UK zones for exposure to driving rain

5.16 If the map given in Diagram 12 is used,determine the national exposure and, whereappropriate, apply the following modifiers:

i) where local conditions accentuatewind effects, such as open hillsides orvalleys where the wind is funnelledonto the wall, add one to thisexposure zone value;

ii) where walls do not face into theprevailing wind, subtract one from thisexposure zone value.

(The national exposure zone value can be moreaccurately calculated from the larger scalemaps and correction factors given in BS8104:1992112).


CWALLS

Wall construction Maximum recommended exposure zone for each construction

Insulation Min. width Impervious cladding Rendered finish Facing masonryMethod of filled or

Full height Above Full height Above Tooled Recessed Flush sills clear cavity

of wall facing of wall facing flush mortar and (mm)

masonry masonry joints joints copings

Built-in full fill 50 4 3 3 3 2 1 1

75 4 3 4 3 3 1 1

100 4 4 4 3 3 1 2

125 4 4 4 3 3 1 2

150 4 4 4 4 4 1 2

Injected fill 50 4 2 3 2 2 1 1not UF foam

75 4 3 4 3 3 1 1

100 4 3 4 3 3 1 1

125 4 4 4 3 3 1 2

150 4 4 4 4 4 1 2

Injected fill 50 4 2 3 2 1 1 1UF foam

75 4 2 3 2 2 1 1

100 4 2 3 2 2 1 1

Partial fill

Residual 50mm cavity 50 4 4 4 4 3 1 1



Internal insulation

Clear cavity50mm 50 4 3 4 3 3 1 1

Clear cavity 100mm 100 4 4 4 4 4 2 2

Fully filled

Cavity 50mm 50 4 3 3 3 2 1 1

Cavity 100mm 100 4 4 4 3 3 1 2

Table 4 Maximum recommended exposure zones for insulated masonry walls

112 BS 8104:1992 Code of practice for assessingexposure of walls to wind-driven rain

Determine the recommended constructionsfrom the modified exposure zone values givenin Table 4. Further guidance as to the use ofthis table is given in BRE Report 262113.

Framed external walls5.17 Any framed external wall will meet therequirement if the cladding is separated fromthe insulation or sheathing by a vented anddrained cavity with a membrane that is vapouropen, but resists the passage of liquid water,on the inside of the cavity (see Diagram 11).

Cracking of external walls5.18 Severe rain penetration may occurthrough cracks in masonry external wallscaused by thermal movement in hot weather orsubsidence after prolonged droughts. Thepossibility of this should be taken into accountwhen designing a building. Detailed guidance isgiven in:

a) BRE Building Elements: Walls, windowsand doors114; and

b) BRE Report 292115;

c) Guidance for choice of materials is givenin BS5628-3:2001116.

Impervious cladding systems forwalls5.19 Cladding systems for walls should:

a) resist the penetration of precipitation tothe inside of the building; and

b) not be damaged by precipitation and notcarry precipitation to any part of the buildingwhich would be damaged by it.

5.20 Cladding can be designed to protect abuilding from precipitation (often driven by thewind) either by holding it at the face of thebuilding or by stopping it from penetratingbeyond the back of the cladding.

5.21 Any cladding will meet the requirement if:

a) it is jointless or has sealed joints, and isimpervious to moisture (so that moisture willnot enter the cladding); or

b) it has overlapping dry joints, isimpervious or weather resisting, and is backedby a material which will direct precipitationwhich enters the cladding towards the outerface.

5.22 Some materials can deteriorate rapidlywithout special care and they should only beused as the weather-resisting part of acladding system if certain conditions are met(see Approved Document supportingRegulation 7, Materials and workmanship). Theweather-resisting part of a cladding systemdoes not include paint nor does it include anycoating, surfacing or rendering which will notitself provide all the weather resistance.

Technical solution

5.23 Cladding may be:

a) impervious including metal, plastic, glassand bituminous products; or

b) weather-resisting including natural stoneor slate, cement based products, fired clay andwood; or

c) moisture-resisting including bituminousand plastic products lapped at the joints, ifused as a sheet material, and permeable towater vapour unless there is a ventilated spacedirectly behind the material; or

d) jointless materials and sealed joints,which would allow for structural and thermalmovement.

5.24 Dry joints between cladding units shouldbe designed so that precipitation will not passthrough them, or the cladding should bedesigned so that precipitation which enters thejoints will be directed towards the exposedface without it penetrating beyond the back ofthe cladding. Note: Whether dry joints aresuitable will depend on the design of thejoint or the design of the cladding and theseverity of the exposure to wind and rain.

5.25 Each sheet, tile and section of claddingshould be securely fixed. Guidance as toappropriate fixing methods is given in BS 8000-6:1990117. Particular care should be taken withdetailing and workmanship at the junctionsbetween cladding and window and dooropenings as they are vulnerable to moistureingress.

5.26 Insulation can be incorporated into theconstruction provided it is either protectedfrom moisture or is unaffected by it.

5.27 Where cladding is supported by timbercomponents or is on the façade of a timberframed building, the space between thecladding and the building should be ventilatedto ensure rapid drying of any water thatpenetrates the cladding.


C WALLS


114 BRE Building Elements series: Walls, windows anddoors, 2002

115 BRE Report BR 292 Cracking in buildings, 1995116 BS 5628-3:2001 Code of practice for use of masonry.

Materials and components, design and workmanship117 BS 8000-6:1990 Workmanship on building sites. Code

of practice for slating and tiling of roofs and claddings


5.28 The requirement can also be met byfollowing the relevant recommendations of:

a) BS CP 143118 for sheet roof and wallcoverings made from the following materials:

Part 1:1958 Corrugated and troughedaluminium

Part 5:1964 Zinc

Part 10:1973 Galvanized corrugated steel

Part 12:1970 (1988) Copper

Part 15:1973 (1986) Aluminium

Part 16:1974 Semi-rigid asbestosbitumen sheets

Recommendations for lead are includedin BS 6915:2001119;

b) BS 8219:2001120;

c) BS 8200:1985121;

d) BS 8297:2000122;

e) BS 8298:1994123;

f) MCRMA Technical Paper 6124;

g) MCRMA Technical Paper 9125.

These documents describe the materials andcontain design considerations includingrecommendations for fixing.

Joint between doors and windows5.29 The joint between walls and door andwindow frames should:


b) not be damaged by precipitation and notpermit precipitation to reach any part of thebuilding which would be damaged by it.

5.30 Damp-proof courses should be providedto direct moisture towards the outside:

a) where the downward flow of moisturewould be interrupted at an obstruction, eg at alintel;

b) where sill elements, including joints, donot form a complete barrier to the transfer ofprecipitation, eg under openings, windows anddoors;

c) where reveal elements, including joints,do not form a complete barrier to the transferof rain and snow, eg at openings, windows anddoors.

5.31 In some cases the width of the cavity dueto thermal insulation and the 50mm clearancefor drainage may be such that the windowframe is not wide enough to completely coverthe cavity closer. The reveal may need linedwith plasterboard, dry lining, a support system,or a thermal backing board. Direct plastering of

the internal reveal should only be used with abacking of expanded metal lathing or similar.

5.32 In areas of the country in driving rainexposure zone 4 checked rebates should beused in all window and door reveals. The frameshould be set back behind the outer leaf ofmasonry, which should overlap it as shown inDiagram 13. Alternatively an insulated finnedcavity closer may be used.

Door thresholds5.33 Where an accessible threshold isprovided to allow unimpeded access, asspecified in Part M, Access to and use ofbuildings, it will meet the requirement if:


CWALLS

118 BS CP 143 Code of Practice for sheet roof and wallcoverings

119 BS 6915:2001 Specification for design andconstruction of fully supported lead sheet roof and wallcoverings

120 BS 8219:2001 Profiled fibre cement. Code of practice121 BS 8200:1985 Code of practice for the design of non-

loadbearing external vertical enclosures of buildings122 BS 8297:2000 Code of practice for design and

installation of non-loadbearing precast concretecladding

123 BS 8298:1994 Code of practice for design andinstallation of natural stone cladding and lining

124 MCRMA Technical Paper 6 Profiled metal roofingdesign guide, revised edition 1996

125 MCRMA Technical Paper 9 Composite roof and wallcladding panel design guide, 1995

Diagram 13 Window reveals for use inareas of severe or verysevere exposure to drivingrain (see paragraph 5.32)

a) the external landing (Diagram 14) is laidto a fall between 1 in 40 and 1 in 60 in a singledirection away from the doorway;

b) the sill leading up to the door thresholdhas a maximum slope of 15°.

Further advice for the development ofaccessible thresholds is given in BRE GBG 47126 and the TSO document127.

External walls (resistance todamage from interstitialcondensation)5.34 An external wall will meet the requirementif it is designed and constructed in accordancewith Clause 8.3 of BS 5250:2002129, and BS ENISO 13788:2001130.

5.35 Because of the high internal temperaturesand humidities, there is a particular risk ofinterstitial condensation in the walls ofswimming pools and other buildings in whichhigh levels of moisture are generated; specialistadvice should be sought when these are beingdesigned.

External walls (resistance tosurface condensation and mouldgrowth)5.36 An external wall will meet the requirementif:

a) it is designed and constructed so that thethermal transmittance (U-value) does notexceed 0.7 W/m2K at any point; and

b) the junctions between elements anddetails of openings, such as doors andwindows, are designed in accordance with the

recommendations in the report on robustconstruction details131, or follow the guidance ofBRE IP17/01132.


C WALLS

Diagram 14 Accessible threshold for use in exposed areas128 (see paragraph 5.33)

126 BRE GBG 47 Level external thresholds: reducingmoisture penetration and thermal bridging, 2001

127 Accessible thresholds in new buildings: guidance forhouse builders and designers, TSO, 1999

128 The drainage channel and adjacent paving andthreshold are usually made up from precast concrete orother pre-formed components





6.1 This section gives guidance for threesituations:

a) Roofs exposed to precipitation from theoutside (see paragraphs 6.3 to 6.9);

b) The risk of interstitial condensation inroofs (see paragraphs 6.10 to 6.13);

c) The risk of condensation or mould growthon the internal surface of roofs (see paragraph6.14).

6.2 Roofs should:


b) not be damaged by precipitation and notcarry precipitation to any part of the buildingwhich would be damaged by it;

c) be designed and constructed so thattheir structural and thermal performance arenot adversely affected by interstitialcondensation.

Roofs (resistance to moisturefrom the outside) 6.3 Roofing can be designed to protect abuilding from precipitation either by holding theprecipitation at the face of the roof or bystopping it from penetrating beyond the backof the roofing system.

6.4 Any roof will meet the requirement if:

a) it is jointless or has sealed joints, and isimpervious to moisture (so that moisture willnot enter the roofing system); or

b) it has overlapping dry joints, isimpervious or weather resisting, and is backedby a material which will direct precipitationwhich enters the roof towards the outer face(as with roofing felt).

6.5 Some materials can deteriorate rapidlywithout special care and they should only beused as the weather-resisting part of a roof ifcertain conditions are met (see ApprovedDocument supporting Regulation 7, Materialsand workmanship133). The weather-resisting partof a roofing system does not include paint nordoes it include any coating, surfacing orrendering which will not itself provide all theweather resistance.

Technical solution

6.6 Roofing systems may be:

a) impervious including metal, plastic andbituminous products; or

b) weather-resisting including natural stoneor slate, cement based products, fired clay andwood; or

c) moisture-resisting including bituminousand plastic products lapped at the joints, ifused as a sheet material, and permeable towater vapour unless there is a ventilated spacedirectly behind the material; or

d) jointless materials and sealed joints,which would allow for structural and thermalmovement.

6.7 Dry joints between roofing sheets shouldbe designed so that precipitation will not passthrough them, or the system should bedesigned so that precipitation which enters thejoints will be drained away without penetratingbeyond the back of the roofing system. Note:Whether dry joints are suitable will dependon the design of the joint or the design ofthe roofing system and the severity of theexposure to wind and rain.

6.8 Each sheet, tile and section of roofshould be fixed in an appropriate manner.Guidance as to appropriate fixing methods isgiven in BS 8000-6:1990134.


6.9 The requirement can also be met byfollowing the relevant recommendations of:

a) BS CP 143135 for sheet roof and wallcoverings made from the following materials:

Part 1:1958 Corrugated and troughedaluminium

Part 5:1964 Zinc

Part 10:1973 Galvanized corrugated steel

Part 12:1970 (1988) Copper

Part 15:1973 (1986) Aluminium

Part 16:1974 Semi-rigid asbestos bitumensheets.

Recommendations for lead are includedin BS 6915:2001136;

b) BS 8219:2001137;

c) BS 8200:1985138;

Section 6: Roofs


CROOFS

133 Approved Document to support Regulation 7: Materialsand workmanship, TSO, 1998 edition (amended 2000)

134 BS 8000-6:1990 Workmanship on building sites. Codeof practice for slating and tiling of roofs and claddings

135 BS CP 143 Code of Practice for sheet roof and wallcoverings

136 BS 6915:2001 Specification for design andconstruction of fully supported lead sheet roof and wallcoverings

137 BS 8219:2001 Profiled fibre cement. Code of practice138 BS 8200:1985 Code of practice for the design of non-

loadbearing external vertical enclosures of buildings

h) MCRMA Technical Paper 6139;

i) MCRMA Technical Paper 9140.

These documents describe the materials andcontain design considerations includingrecommendations for fixing.

Roofs (resistance to damage frominterstitial condensation)6.10 A roof will meet the requirement if it isdesigned and constructed in accordance withClause 8.4 of BS 5250:2002141 and BS EN ISO13788:2001142. Further guidance is given in theBRE Report BR 262143.

6.11 The requirement will be met by theventilation of cold deck roofs, i.e. those roofswhere the moisture from the building canpermeate the insulation. For the purposes ofhealth and safety it may not always benecessary to provide ventilation to small roofssuch as those over porches and bay windows.Although a part of a roof which has a pitch of70° or more is to be insulated as though it werea wall, the provisions in this document apply toroofs of any pitch.

6.12 To avoid excessive moisture transfer toroof voids gaps and penetrations for pipes andelectrical wiring should be filled and sealed;this is particularly important in areas of highhumidity, eg bathrooms and kitchens. Aneffective draught seal should be provided toloft hatches to reduce inflow of warm air andmoisture.

6.13 Because of the high internal temperaturesand humidities, there is a particular risk ofinterstitial condensation in the roofs ofswimming pools and other buildings in whichhigh levels of moisture are generated; specialistadvice should be sought when these are beingdesigned.

Roofs (resistance to surfacecondensation and mould growth)6.14 A roof will meet the requirement if:

a) it is designed and constructed so that thethermal transmittance (U-value) does notexceed 0.35 W/m2K at any point; and

b) the junctions between elements and thedetails of openings, such as windows, aredesigned in accordance with therecommendations in the report on robustconstruction details144, or follow the guidance ofBRE IP17/01145 or MCRMA Paper 14146 forprofiled metal roofing.


C ROOFS

139 MCRMA Technical Paper 6 Profiled metal roofingdesign guide, revised edition 1996

140 MCRMA Technical Paper 9 Composite roof and wallcladding panel design guide, 1995






146 MCRMA Technical Paper 14 Guidance for the design ofmetal roofing and cladding to comply with approveddocument L2:2001, 2002

3 BS 7913: 1998 Guide to the principles of theconservation of historic buildings14, 36 BS 5930:1999 Code of practice for siteinvestigations21 BS 8103-1:1995 Structural design for low risebuildings37 BS 10175:2001 Investigation of potentiallycontaminated land. Code of practice48 BS 3882:1994 Specification for topsoil84, 89 BS 8500-1: 2002 Concrete. ComplementaryBritish Standard to BS EN 206-1. Method ofspecifying and guidance for the specifier86 BS 1282:1999 Wood preservatives. Guidanceon choice, use and application87, 94 BS CP 102:1973 Protection of buildingsagainst water from the ground88, 102 BS 8102:1990 Code of practice forprotection of structures against water from theground90, 116 BS 5628-3:2001 Code of practice for useof masonry. Materials and components, designand workmanship91 BS 7331:1990 Specification for directsurfaced wood chipboard based onthermosetting resins92 BS EN 312-5:1997 Particleboards.Specifications. Requirements for load-bearingboards for use in humid conditions96, 129, 141 BS 5250:2002 Code of practice for thecontrol of condensation in buildings97, 130, 142 BS EN ISO 13788:2001 Hygrothermalperformance of building components andbuilding elements. Internal surface temperatureto avoid critical surface humidity and interstitialcondensation. Calculation methods101 BS 8215:1991 Code of practice for designand installation of damp-proof courses inmasonry construction103, 112 BS 8104:1992 Code of practice forassessing exposure of walls to wind-driven rain104, 107, 108 BS 5628-3:2001 Code of practice foruse of masonry. Materials and components,design and workmanship105 BS EN 998-2:2002 Specification of mortarfor masonry106 BS 5262:1991 Code of practice for externalrenderings109 BS 5617:1985 Specification for urea-formaldehyde (UF) foam systems suitable forthermal insulation of cavity walls with masonryor concrete inner and outer leaves110 BS 5618:1985 Code of practice for thermalinsulation of cavity walls (with masonry or

concrete inner and outer leaves) by filling withurea-formaldehyde (UF) foam systems111 BS 8208, Part 1:1985 Guide to assessmentof suitability of external cavity walls for fillingwith thermal insulation117, 134 BS 8000-6:1990 Workmanship on buildingsites. Code of practice for slating and tiling ofroofs and claddings118, 135 BS CP 143 Code of Practice for sheet roofand wall coverings119, 136 BS 6915:2001 Specification for designand construction of fully supported lead sheetroof and wall coverings120, 137 BS 8219:2001 Profiled fibre cement. Codeof practice121, 138 BS 8200:1985 Code of practice for thedesign of non-loadbearing external verticalenclosures of buildings122 BS 8297:2000 Code of practice for designand installation of non-loadbearing precastconcrete cladding123 BS 8298:1994 Code of practice for designand installation of natural stone cladding andlining

British Standards available from: BSI, PO Box16206, Chiswick, London, W4 4ZL. Website:www.bsonline.techindex.co.uk

British Standards referred to


CBRITISH STANDARDS REFERRED TO

Arup Environmental73 DETR/ Arup Environmental PIT ResearchReport: Passive venting of soil gases beneathbuildings, 1997

Available from Arup website:www.arup.com/environmental/HTML/Reports/PassiveVenting.htm

Association of Geotechnical andGeoenvironmental Specialists (AGS)35 Guidelines for combined geoenvironmentaland geotechnical investigations, Association ofGeotechnical and Geoenvironmental Specialists

Available from: AGS, Forum Court, 83 CopersCope Road, Beckenham, Kent, BR3 1NR.Website:www.ags.org.uk/publications/pubcat.cfm

British Geological Survey (BGS)63 BGS Technical Report WP/95/1 Methane,carbon dioxide and oil seeps from naturalsources and mining areas: characteristics,extent and relevance to planning anddevelopment in Great Britain, 1995

Available from: BGS Sales Desk, Keyworth,Nottingham, NG12 5GG. Website:www.bgs.ac.uk

Building Research Establishment (BRE)5 BRE Report BR 267 Major alterations andconversions: A BRE guide to radon remedialactions in existing buildings, 19946, 78 BRE Good Building Guide GBG 25 Buildingsand radon, 19969, 57 BRE for Scottish Office Design guidance onflood damage for dwellings, TSO, 199615 BRE Digest 322 Site investigation for low-risebuilding: procurement, 198716 BRE Digest 318 Site investigation for low-risebuilding: desk studies, 198717 BRE Digest 348 Site investigation for low-risebuilding: the walk-over survey, 198918 BRE Digest 381 Site investigation for low-risebuilding: trial pits, 199319 BRE Digest 383 Site investigation for low-risebuilding: soil description, 199320 BRE Digest 411 Site investigation for low-risebuilding: direct investigations, 199522 BRE Digest 298 Low-rise buildingfoundations: the influence of trees in clay soils,199923 BRE Digest 241 Low rise buildings onshrinkable clay soils: Part 2, 1993

24 BRE Digest 242 Low rise buildings onshrinkable clay soils: Part 3, 199327 BRE Digest 427 Low-rise buildings on fill28 BRE Report BR 424 Building fill: Geotechnicalaspects, 200133, 85 BRE Special Digest SD1 Concrete inaggressive ground, 2003

Part 1: Assessing the chemicalenvironment

Part 2: Specifying concrete andadditional protective measures

Part 3: Design guide for commonapplications

Part 4: Design guide for precast products74, 80 BRE/ Environment Agency Report BR 414Protective measures for housing on gas-contaminated land, 200175, 81 BRE Report BR 211 Radon: guidance onprotective measures for new dwellings, 1999. 77 BRE Report BR 293 Radon in the workplace,199583 BRE Digest 276 Hardcore, 199293 BRE Digest 429 Timbers and their naturaldurability and resistance to preservativetreatment, 199898, 113, 143 BRE Report BR 262 Thermal insulation:avoiding risks, 2002100, 132, 145 BRE Information Paper IP17/01Assessing the effects of thermal bridging atjunctions and around openings, 2001114 BRE Building Elements series: Walls,windows and doors, 2002115 BRE Report BR 292 Cracking in buildings,1995126 BRE GBG 47 Level external thresholds:reducing moisture penetration and thermalbridging, 2001

Available from: CRC Ltd, 151 RoseberyAvenue, London, EC1R 4QX. Website:www.brebookshop.com

Chartered Institution of Wastes Management(CIWM)61 Monitoring of landfill gas, CharteredInstitution of Wastes Management (CIWM), 2ndedition 1998

Available from: CIWM Publications Department,9 Saxon Court, St Peter's Gardens,Northampton, Northamptonshire, NN1 1SX.Website: www.ciwm.co.uk

Other documents referred to


C OTHER DOCUMENTS REFERRED TO

Construction Industry Research andInformation Association (CIRIA)10 CIRIA/ Environment Agency Flood products.Using flood protection products – a guide forhome owners, 2003. Available from Website:www.ciria.org/flooding.47 CIRIA Report 132 A guide to safe workingpractices for contaminated land, 199349 CIRIA Special Publication SP124 Barriers,liners and cover systems for containment andcontrol of land contamination, 199650 CIRIA Special Publication SP102Decommissioning, decontamination anddemolition, 199551 CIRIA Special Publication SP104Classification and selection of remedialmethods, 199552 CIRIA Special Publication SP105 Excavationand disposal, 199553 CIRIA Special Publication SP106 Containmentand hydraulic measures, 199654 CIRIA Special Publication SP107 Ex-situremedial methods for soils, sludges andsediments, 199555 CIRIA Special Publication SP109 In-situmethods of remediation, 199565 CIRIA Report 130 Methane: its occurrenceand hazards in construction, 199366 CIRIA Report 131 The measurement ofmethane and other gases from the ground,199367 CIRIA Report 150 Methane investigationstrategies, 199568 CIRIA Report 151 Interpreting measurementsof gas in the ground, 199569 CIRIA Report 152 Risk assessment formethane and other gases from the ground,199572 CIRIA Report 149 Protecting developmentfrom methane, 199579 CIRIA Publication C506 Low-cost options forprevention of flooding from sewers, 1998

Available from: CIRIA, Classic House, 174-180Old Street, London, EC1V 9BP. Website:www.ciria.org.uk

Department for Environment, Food and Ruralaffairs (Defra)29 Department of the Environment IndustryProfiles, 1996

Available from: Defra Publications, c/o IFORCELtd, Imber Court Business Park, Orchard Lane,East Molesey, Surrey, KT8 OBZ

Environment Agency30, 40 Defra/ Environment Agency ContaminatedLand Research Report CLR 8 Prioritycontaminants for the assessment of land, 200231 Environment Agency R & D Technical ReportP291 Information on land quality in England:Sources of information (including backgroundcontaminants)32 Environment Agency R & D Technical ReportP292 Information on land quality in Wales:Sources of information (including backgroundcontaminants)38 National Groundwater & Contaminated LandCentre report NC/99/38/2 Guide to goodpractice for the development of conceptualmodels and the selection and application ofmathematical models of contaminant transportprocesses in the subsurface, EnvironmentAgency, 2001

Available from website: www.environment-agency.gov.uk/subjects/waterres/groundwater/39 Defra/Environment Agency ContaminatedLand Research Report CLR 7 Assessment ofrisks to human health from land contamination:an overview of the development of soilguideline values and related research, 200241 Defra/Environment Agency ContaminatedLand Research Report CLR 9 Contaminants insoil: collation of toxicological data and intakevalues for humans, 200242 Defra/Environment Agency ContaminatedLand Research Report CLR 10 Thecontaminated land exposure assessment model(CLEA): technical basis and algorithms, 200243, 71 Defra/Environment Agency ContaminatedLand Research Report CLR 11 Handbook ofmodel procedures for the management ofcontaminated land (in preparation)44 Environment Agency R & D Technical ReportP5-065 Technical aspects of site investigation,200045 Environment Agency R & D Technical ReportP5-066 Secondary model procedure for thedevelopment of appropriate soil samplingstrategies for land contamination59 Assessment and management of risks tobuildings, building materials and services fromland contamination, Environment Agency, 200170 Environment Agency GasSIM - Landfill gasassessment tool.

Available from website: www.gassim.co.uk.

CLR, SGV, TOX and other technical reportsavailable from: Environment Agency R & DDissemination Centre, c/o WRc, FranklandRoad, Swindon, Wilts SN5 8YF. Websites:www.defra.gov.uk/environment/landliability/pubs.htm#5 andwww.eareports.com/ea/rdreport.nsf


COTHER DOCUMENTS REFERRED TO

Foundation for the Built Environment (FBE)25 Subsidence damage to domestic buildings:lessons learned and questions remaining, FBE,2000

Available from CRC Ltd, 151 Rosebery Avenue,London, EC1R 4QX. Website:www.brebookshop.com

Foundation for Water Research (FWR)58 Foundation for Water Research report FR0448Laying potable water pipelines in contaminatedground: guidance notes, 1994

Available from FWR, Allen House, The Listons,Liston Road, Marlow, Bucks SL7 1FD. Website:www.fwr.org

Health and Safety Executive (HSE)46 HSE Report HSG 66 Protection of workersand the general public during the developmentof contaminated land, 1991

Available from HSE Books, PO Box 1999,Sudbury, Suffolk, CO10 2WA. Website:www.hsebooks.co.uk

Her Majesty’s Inspectorate of Pollution(HMIP)60 HMIP Waste Management Paper No 27 Thecontrol of landfill gas, TSO, 2nd edition 1991

Institute of Petroleum (IP)62 Institute of Petroleum TP 95 Guidelines forinvestigation and remediation of petroleumretail sites, 1998

Available from Portland Customer Services,Portland Press Ltd, Commerce Way, WhitehallIndustrial Estate, Colchester, CO2 8HP.Website: www.petroleum.co.uk

Metal Cladding and Roofing ManufacturersAssociation (MCRMA)124, 139 MCRMA Technical Paper 6 Profiled metalroofing design guide, revised edition 1996125, 140 MCRMA Technical Paper 9 Composite roofand wall cladding panel design guide, 1995146 MCRMA Technical Paper 14 Guidance for thedesign of metal roofing and cladding to complywith approved document L2:2001, 2002

Available from: MCRMA Ltd, 18 Mere FarmRoad, Prenton, Wirral, Cheshire, CH43 9TT.Website: www.mcrma.co.uk

National House-Building Council (NHBC)26 NHBC Standards Chapter 4.2 Building neartrees, 2003

Available from NHBC, Buildmark House,Chiltern Avenue, Amersham, Bucks HP6 5AP.Website: www.nhbc.co.uk

Office of the Deputy Prime Minister (ODPM)8, 56, 95 Preparing for floods: interim guidance forimproving the flood resistance of domestic andsmall business properties, DTLR, 2002.

Available from website:www.safety.odpm.gov.uk/bregs/floods/index.htm

Society for the Protection of AncientBuildings (SPAB)4 SPAB Information Sheet 4 The need for oldbuildings to breathe, 1986

Available from The Society for the Protection ofAncient Buildings, 37 Spital Square, London,E1 6DY. Website: www.spab.org.uk

The Stationery Office (TSO)7 Planning Policy Guidance Note PPG 25Development and flood risk, DTLR, 2001.Available from website:www.odpm.gov.uk/stellent/groups/odpm_control/documents/contentservertemplate/odpm_index.hcst?n=2263&l=212 Planning Policy Guidance Note PPG 23:planning and pollution control, ODPM, 1997.Available from website:www.odpm.gov.uk/stellent/groups/odpm_control/documents/contentservertemplate/odpm_index.hcst?n=2263&l=264 Methane and other gases from disused coalmines: the planning response, TSO, 199699, 131, 144 Limiting thermal bridging and airleakage: robust construction details fordwellings and similar buildings, TSO, 2001127 Accessible thresholds in new buildings:guidance for house builders and designers,TSO, 1999133 Approved Document to support Regulation 7:Materials and workmanship, TSO, 1998 edition(amended 2000)

Available from: TSO, PO Box 29, Norwich NR31GN; Tel: 0870 600 5522. Website:www.tso.co.uk


C OTHER DOCUMENTS REFERRED TO

A.1 A substantial amount of guidance on theassessment of contaminated land has beenpublished to support the implementation ofPart IIA of the Environmental Protection Act1991. Most of this guidance is contained in thejoint Defra/Environment Agency ContaminatedLand Research Reports (CLRs). This guidancecan be used to support the assessmentprocess set out in Section 2. A summary of thereports is set out below and an outline of theprocess is given in Figure A1147.

A.2 For health, risk estimation can be carriedout using generic assessment criteria such ascontaminant Soil Guideline Values (SGVs) orrelevant and appropriate environmentalstandards. SGVs represent contaminantconcentrations which may pose unacceptablerisks to health. The development of SGVs for arange of priority contaminants is described inthe Defra/ Environment Agency reports CLR7148, CLR 8149, CLR 9150 and CLR 10151.

A.3 CLR 10 describes the Contaminated LandExposure Assessment Model (CLEA) forderiving SGVs for three different site uses: (i)residential, (ii) residential with plant uptake and(iii) commercial/ industrial. In this way therelative importance of each of the pollutantlinkages is considered. For example, forresidential site use it is assumed residentshave private gardens and/ or access tocommunity open space close to the home andthat some may use their gardens to growvegetables. CLR 10 gives details of theconceptual model underpinning each of thestandard land uses.

A.4 A series of Defra/Environment AgencySGV reports152 contain SGVs for a range ofcontaminants, one report for each contaminant,and the corresponding TOX reports153 containthe toxicological data used to derive the SGVs.SGVs should be used only in conjunction withthe CLR 7 to 10 reports and associated SGVand TOX reports.

A.5 The use of ICRCL (InterdepartmentalCommittee on the Redevelopment ofContaminated Land) document Guidance Note59/83:Guidance on the assessment andredevelopment of Contaminated Land 154 is nolonger appropriate in health risk assessmentand has been withdrawn155 by Defra.

A.6 CLR 7 provides advice regarding suchissues. In certain cases the most appropriateaction may be to redesign the building layout.Further guidance can be obtained from theEnvironment Agency/ NHBC R & D Publication66156.

A.7 An alternative to the generic approach isto undertake a more site specific quantitativerisk assessment using the principles of riskassessment or a risk assessment model.Specialist advice should be sought.

Annex A: Guidance on the assessment ofland affected by contaminants


CGUIDANCE

References to Annex A

Department for Environment, Food and RuralAffairs (Defra)155 Defra Contaminated Land Advice Note CLAN3/02: Withdrawal of ICRCL Trigger Values, 2002

Available fromwww.defra.gov.uk/environment/landliability/pdf/clan3-02.pdf

Environment Agency147 Defra/ Environment Agency ContaminatedLand Research Report CLR 11 Handbook ofmodel procedures for the management ofcontaminated land (in preparation)148 Defra/ Environment Agency ContaminatedLand Research Report CLR 7 Assessment ofrisks to human health and land contamination:an overview of the development of soilguideline values and related research, 2002149 Defra/ Environment Agency ContaminatedLand Research Report CLR 8 Prioritycontaminants for the assessment of land, 2002150 Defra/ Environment Agency ContaminatedLand Research Report CLR 9 Contaminants insoil: collation of toxicological data and intakevalues for humans, 2002151 Defra/ Environment Agency ContaminatedLand Research Report CLR 10 Thecontaminated land exposure assessment model(CLEA): technical basis and algorithms, 2002152 Defra/ Environment Agency Soil GuidelineValue reports (separate SGV report for eachcontaminant), 2002153 Defra/ Environment Agency TOX reports(separate TOX report for each contaminant),2002156 Environment Agency/ NHBC R & DPublication 66 Guidance for the safedevelopment of housing on land affected bycontamination, TSO, 2000

CLR, SGV, TOX and other technical reportsavailable from: Environment Agency R & DDissemination Centre, c/o WRc, FranklandRoad, Swindon, Wilts SN5 8YF. Websites:www.defra.gov.uk/environment/landliability/pubs.htm#5 andwww.eareports.com/ea/rdreport.nsf

Inter-Departmental Committee on theRedevelopment of Contaminated Land(ICRCL)154 ICRCL Guidance Note 59/83 Guidance onthe assessment and redevelopment ofcontaminated land, 2nd edition, 1987


C ANNEX A: GUIDANCE

Site p

reparatio

n and resistance to

contam

inants and m

oisture

Ap

proved

Docum

ent C47

CA

NN

EX

A: G

UID

AN

CE

Note: T

he process may apply to one or m

ore pollutant linkages each of which m

ay follow a different route. F

or some linkages, it ¤

may be possible to stop at an early stage – others w

ill progress all the way through the process.¤

The level of com

plexity of each stage may also vary and in som

e cases may be very sim

ple.

START Define the context ¤& set the objectives

Define the context & set ¤or refine the objectives

Define the context & set ¤or refine the objectives

NO FURTHER¤ACTION¤

REQUIRED

NO FURTHER¤ACTION¤

REQUIRED

Preliminary risk¤assessment

Identification of feasible¤remediation options

Are¤there potential¤

risks?

Yes

Yes

Yes

Yes Yes

Yes

Are¤there unacceptable¤

risks?

Can an ¤appropriate stragety¤

be identified?

Detailed quantitative ¤risk assessment

Development of the¤remediation strategy

Can the¤most appropriate option¤

(or combination of options)¤be selected?

Are¤there unacceptable¤

risks?

Generic quantatitive¤risk assessment

Detailed evaluation of¤options

Is¤assessment using¤site specific criteria¤

appropriate?

Is¤assessment ¤

using generic criteria¤appropriate?

Is¤further assessment¤

required?

Have¤feasible options been¤

identified?

No

No

No

No

Not known

Not known

Not ¤known

Collect more¤site data¤& review¤

assessment


assessment

Collect ¤more data,¤

review¤objectives¤or monitor¤condition


assessment

NoNo

No

No No

Yes

Yes

Preparation of the¤implementation plan

Are the¤monitoring data¤

acceptable?

Long-term monitoring¤& maintenance

Are long¤term monitoring data ¤

required?

Design, implementation &¤verification of the works

Have the ¤works been¤

verified?

Is the¤implementation plan¤

agreed with all¤parties?

YesYes

Yes

Yes

Collect ¤more data¤&/or review¤objectives

Review¤decisions¤

taken earlier¤in the process

Yes

No

No

No

Yes

Adjust design¤and/or¤

arrangements¤for supervision

Adjust plan until¤agreement is¤

reached

Is¤further¤

remediation¤required?

No

No

RISK ASSESSMENT OPTIONS APPRAISAL IMPLEMENTATION OF RISKMANAGEMENT ACTION

Diagram

A1

Th

e pro

cess of m

anag

ing

land

affected b

y con

tamin

ants


C

Printed in the United Kingdom for TSOD166157 C100 06/04

The following documents have been approvedand issued by the First Secretary of State forthe purpose of providing practical guidancewith respect to the requirements of the BuildingRegulations 2000.

Approved Document A – Structure: 1992edition, fourth impression (with amendments)1994, further amended 2000

Approved Document B – Fire safety:2000 edition, amended 2002

Approved Document C – Site preparationand resistance to contaminants andmoisture: 2004 edition

Approved Document D – Toxic substances:amended 1992, further amended 2000

Approved Document E – Resistance to thepassage of sound: 2003 edition

Approved Document F – Ventilation:1995 edition, amended 2000

Approved Document G – Hygiene:1992 edition, second impression (withamendments) 1992, further amended 2000

Approved Document H – Drainage and WasteDisposal: 2002 edition

Approved Document J – Combustionappliances and fuel storage systems:2002 edition

Approved Document K – Protection fromfalling, collision and impact: 1998 edition,amended 2000

Approved Document L1 – Conservation offuel and power in dwellings: 2002 edition

Approved Document L2 – Conservation offuel and power in buildings other thandwellings: 2002 edition

Approved Document M – Access to and useof buildings: 2004 edition

Approved Document N – Glazing – safety inrelation to impact, opening and cleaning:1998 edition, amended 2000

Approved Document to support regulation 7– Materials and workmanship: 1999 edition,amended 2000

Site preparation and resistance to contaminants and moistureApproved Document C

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CAPPROVED DOCUMENTS

Approved Documents

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