conversions and renovations

8/20/2019 Conversions and Renovations

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STANDARDSfor

Conversions and renovations

April 2005 edition

Effective from July 2005


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Conversions and Renovations

CONTENTS Clause Page

INTRODUCTION 1

Technical Requirements R1 – R6 3

Procedural flowchart 6

Survey of existing building C1 7

Design Standard C2 7

Completed work C3 7

Building Regulations C4 8

Insured guarantees/warranties C5 8

Wood rot and beetle infestation C6 8

Vermin and pest infestation C7 9

Foundations C8 9

Basements and structuralwaterproofing (tanking) C9 10

Drainage below ground C10 11

Ground floors C11 11

Walls C12 – C15 12

Chimneys and flues C16 16

Upper floors C17 & C18 16

Staircases, stairways and landings C19 17

Pitched roofs C20 17

Flat roofs and balconies C21 18

Roof drainage C22 19

Framed buildings C23 & C24 19

Doors, windows and glazing C25 20

Joinery C26 20

Floor, wall and ceiling finishes C27 21

Services C28 – C33 21

Painting and decorating C34 22

External works C35 – C39 22

Provision of information C40 & C41 23

APPENDIX A

Useful contacts and relevant publications 24

APPENDIX B

Survey(s) of existing buildings 26

Introduction NHBC Standards for Conversions and Renovations

Effective: July 2005 April 2005 edition

INTRODUCTION


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PURPOSE

The Standards for Conversions and Renovations

provide guidance on the type of project that willbe acceptable to NHBC, the scope of the survey(s)and work that will be required.

WHAT ARE ‘CONVERSIONSAND RENOVATIONS’?

Conversions and renovations are projects thatinvolve work to existing buildings or parts ofexisting buildings. Examples include:

• the conversion of industrial or commercialbuildings into housing

• the conversion of an existing residential buildinginto flats

• the addition of an additional storey to anexisting building

• the renovation of an existing residential building.

WHICH STANDARDS APPLY?

New work that forms part of the conversion orrenovation should be carried out in accordancewith the NHBC Standards.

Other conversion or renovation work should becarried out in accordance with these Standards forConversions and Renovations.

The Standards for Conversions and Renovationscurrent at the time work is started, shall apply.

SURVEY(S)

The builder should arrange for survey(s) of thebuilding to be carried out in accordance with ClauseC1 before applying to NHBC for Buildmark cover.

A copy of the survey report(s), including any specialistreports, should accompany the application forBuildmark cover. The reports will be used to establishif the project is acceptable for Buildmark cover.

NHBC may impose specific requirements forthe project, which must be complied with as acondition of providing Buildmark cover.

NHBC relies on the details supplied by the builderwhen it accepts a project for Buildmark cover.Acceptance of a project does not absolve the

builder from obligations under the Rules andBuildmark in respect of any defects, whether ornot they are located in parts of the building coveredby the reports or NHBC’s specific requirements.

TECHNICAL REQUIREMENTS

The Technical Requirements are printed in red.

They are mandatory and MUST be met bythe builder.

Technical Requirements R1 to R5 inclusiveare the same as those in the NHBC StandardsChapter 1.1 ‘Introduction to the Standards andTechnical Requirements’.

Technical Requirement R6 relates specificallyto the Standards for Conversionsand Renovations.

PERFORMANCE STANDARDS

The Performance Standards are printed in dark blueand will assist builders in meeting the TechnicalRequirements. By meeting each PerformanceStandard the Technical Requirement will be met.

Alternative standards of performance will beacceptable ONLY if, in the opinion of NHBC,the Technical Requirements are met and thestandard achieved is not lower than the statedPerformance Standard.

GUIDANCEGuidance on how the Performance Standard may bemet is printed in light blue.

Guidance is based on normal construction proceduresand recommended practices that have been shown tobe satisfactory and acceptable over time.

Due to the scope of buildings which could beconsidered for conversion or renovation, the guidancemay need to be varied for particular cases. NHBC willconsider other methods proposed to meet specificrequirements, subject to consultation and evaluation.

Some irregularities in the existing background andfinish, beyond normal building tolerances, may beacceptable for conversions and renovations.

INTERPRETATION

Occasionally there may be disagreements on howTechnical Requirements and Performance Standardsare to be interpreted. Such cases are usually resolvedthrough further consultation, failing which, NHBC willexercise its right to decide.

NHBC Standards for Conversions and Renovations Page 1 of 31

April 2005 edition Effective: July 2005

INTRODUCTION


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TESTING

To establish whether the existing building or parts of

it are adequate it may be necessary to carry out tests,both on the structure and materials that are to beretained. These tests (where required) will be at thebuilder’s expense.

Tests on the structure to be retained shall be inaccordance with European or National Standards asappropriate. Where suitable tests are not specified inEuropean or National Standards, then builders maybe required to obtain the services of a specialist todetermine them.

New materials, reclaimed or retained materialsshall comply with Technical Requirement R3.

STANDARDS, CODES OFPRACTICE AND OTHERAUTHORITATIVE DOCUMENTS

Where the Standards for Conversions andRenovations refer to:

• NHBC Standards

• European Standards

• British Standards

• Codes of Practice

• Authoritative documents or

• Technical approval certificationthe documents shall be the editions current at thetime the work is started unless otherwise agreed byNHBC in writing.

The Standards for Conversions and Renovationscontain references to authoritative documents.These references are not exhaustive and NHBCwill consider recommendations from otherauthoritative organisations.

LIMITATIONS ON USE

The Technical Requirements, Performance Standardsand Guidance do not form a complete specificationand should not be used as such in contracts.

Page 2 of 31 NHBC Standards for Conversions and Renovations


INTRODUCTION


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R1 Statutory requirementsWork shall comply with all relevantBuilding Regulations and otherstatutory requirements relating tothe completed construction work

In England, Wales and the Isle of Man,NHBC will generally accept work that accordswith the relevant Approved Documents andtheir supporting documents. Exceptions wouldbe where NHBC has a higher standard or wherethere is doubt as to whether the recommendationin the Approved Document is appropriate to a

particular application.In Scotland and Northern Ireland, accountshall be taken of the relevant Building Standardsand Regulations.

Building Regulations and rules of StatutoryAuthorities primarily cover matters of healthand safety. Matters affecting durability andserviceability also need to be considered.

NHBC Standards do not apply to:

• health and safety matters relating tobuilding operations

• handling and use of certain building materials• planning matters.

R2 Design requirement

Design and specification shallprovide satisfactory performance

Account shall be taken of:

(a) The land quality, including:

(i) climate

(ii) topography

(iii) geology and ground conditions

(iv) contamination

(v) workings below ground

(vi) previous use of the site

(vii)any other aspect, on or adjacent to the site,which could affect the design.

Where appropriate, the land quality will have to bedetermined by a person acceptable to NHBC.

The builder shall ensure that the work complies with the Technical Requirements

(b) The structural adequacy of the works. The design,with appropriate factors of safety, shouldsatisfactorily allow for loads during and afterconstruction and for their transfer to thesupporting structure, or foundation, withoutundue movement, including:

(i) self weight

(ii) all imposed loads, including wind loads

(iii) construction loads.

(c) The geographical location of the site, including:

(i) climate

(ii) topography

(d) The position of the dwelling on the site, especiallywith reference to the dwelling’s exposure to theweather, including exposure at early stages inthe development of a site, even if it is eventuallyprotected by structures built later.

(e) The position of building elements within theconstruction works, including the inter-relationshipof materials and constructions.

(f) The security of the dwellings.

R3 Materials requirementAll materials, products and buildingsystems shall be suitable for theirintended purpose

The structure of the home shall, unless specificallyagreed otherwise in writing with NHBC, have a lifeof at least 60 years. Individual components andassemblies, not integral to the structure, may havea lesser durability and need planned maintenance,repair or replacement during that period.

Proper account shall be taken of the use andlocation of materials, products and buildingsystems in relation to:

• durability of both the structure andindividual components and assemblies

• geographical location

• position on the site

• position within the structure.Materials, products and building systems will normallybe acceptable if they comply with the following:

(a) MATERIALS AND PRODUCTS USED FORCRITICAL FUNCTIONS

Functions critical to performance are:structure, fire resistance, weatherproofing,durability, thermal and sound insulation,services including heating appliances and flues.





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R3 (continued)Any of the following are acceptable:

(i) performance in accordance with standardsset by NHBC,or(ii) where no NHBC standard is set, compliancewith the relevant British Standard or equivalentEuropean Technical Specification approved by aCommittee for Standardisation, provided theyare used in accordance with the relevant Codeof Practice,or

(iii) compliance with standards not lower thanthose defined in a relevant British Standardspecification or equivalent, provided theiruse is accepted by NHBC,or(iv) satisfactory assessment by an appropriateindependent technical approvals authorityaccepted by NHBC, including: British Board ofAgrément (BBA), Building Research Establishment(BRE) or a body authorised under Annex 4 tothe Construction Products Directive,or(v) use of materials and products in accordance

with well established satisfactory custom andpractice, provided that such custom and practiceis acceptable to NHBC,or(vi) acceptance, in writing, by NHBC that thequality and use is satisfactory.

(b) MATERIALS AND PRODUCTS USED FORNON-CRITICAL FUNCTIONSCompliance with the above acceptancecriteria for critical functions or strictly inaccordance with manufacturers’recommendations for the specific use.

(c) RECLAIMED MATERIALSReclaimed materials may only be re-used with theprior agreement of NHBC. Independent certificationof suitability may be required.

(d) PROPRIETARY BUILDING SYSTEMSReference should be made to R3(a), (iv).

(e) TIMBER DURABILITYReference should be made to Chapter 2.3 ‘Timberpreservation (natural solid timber)’ (each section).

Note

Equivalents to British Standards or technical approvals

authority shall be those accepted in the UK.

R4 Workmanship requirement

All work shall be carried out in aproper, neat and workmanlike manner

The Builder shall ensure that:

(a) the conditions of the materials, productsand the completed work are satisfactory

(b) appropriate precautions are taken toprevent damage

(c) account is taken of the following:

(i) the requirements of the design

(ii) suitable methods of unloading and handling

(iii) proper protection during storage

(iv) use of correct installation methods

(v) protection against weather duringconstruction (including excessive heat,cold, wetting or drying)

(vi) protection against damage by following trades.

R5 Structural design requirement

Structural design shall be carriedout by suitably qualified personsin accordance with BritishStandards and Codes of Practice

The following shall be designed by Chartered Civilor Structural Engineers whose status (includingprofessional indemnity insurance) is accepted by NHBC:

(a) foundations on hazardous ground where thehazard makes special consideration necessary.This would not apply to matters for which NHBCsets Standards, such as building near trees,except where specified to the contrary

(b) foundations and superstructure of everybuilding over three storeys in height

(c) certain types of foundations and retaining walls,

as required in the individual Chapters of theNHBC Standards

(d) any structural element which is not basedon specific design criteria as laid down in theChapters of the NHBC Standards

(e) any dwelling not constructed in accordancewith UK traditional practice.

Other structural elements may be designed by aChartered Civil or Structural Engineer or otherswhose status (including professional indemnityinsurance) is accepted by NHBC.





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The structural design shall take account of thedurability requirement in Technical RequirementR3 Materials requirement.

In England, Wales, Northern Ireland and theIsle of Man, structural design may be undertakenby the Builder’s own Engineer or a ConsultingEngineer employed by the Builder. Where specialistsubcontractors undertake the design, it must beseparately appraised by the Builder’s own Engineeror by a Consulting Engineer employed by theBuilder to ensure that the site investigation,choice of foundations, siting and constructionof dwellings are properly taken into account andthat the design is appropriate for the loadingand conditions.

In Scotland, the Engineer shall be independent ofthe Builder and specialist subcontractor.

Account shall be taken of the following BritishStandards and Codes of Practice or their Europeanequivalents or such codes and standards as maysupersede them:

BS 5268 Structural use of timber

BS 5628 Code of Practice for use of masonry

BS 5950 Structural use of steel work in building

BS 6399 Loading for buildings

BS 8004 Code of Practice for foundations

BS 8110 Structural use of concrete

Alternatively, designs in accordance withBS 8103 ‘Structural design of low rise buildings’will be acceptable.

The Builder shall:

• require the Engineer to issue clear instructionsfor site personnel

• not permit departure from the design withoutthe Engineer’s written consent

• require the Engineer or his representative tocarry out such inspections as may be requiredby NHBC to ensure the adequacy of the designand construction.

The Builder shall ensure that the Engineer visits thesite during construction:

(i) when the foundations have been designedunder this Technical Requirement, or

(ii) when specifically required by NHBC inthese Standards.

The Engineer shall satisfy himself that the design issuitable for the conditions encountered on the site

of each dwelling.

When requested by NHBC, the Builder shall:

• produce such design documents, calculationsand prescribed forms of certification as NHBCrequires for scrutiny

• provide design documents and assemblyinstructions, solely for the use of NHBC staff

• arrange for NHBC staff to have access to placeswhere off-site fabrication is taking place.

R6 Survey requirement forconversions and renovations

Existing buildings shall be surveyedto determine their condition and thework required to bring them into a

durable and habitable state

The survey(s) should be carried out in accordancewith clause C1.

A detailed survey should be carried out by acompetent and qualified person with relevantknowledge and experience (e.g. an RICS BuildingSurveyor), whose status (including professionalindemnity insurance) is accepted by NHBC.

Specialist surveys should be carried out by suitablyqualified and experienced specialist surveyors.

Account shall be taken of:

• the former use of the building

• the present condition of the building

• any previous conversion and renovation works

• the geographical location

• any tests required to confirm the suitabilityof the existing structure and/or materials

• the structural condition of the existingbuilding and the effect of the proposedconversion and renovation works.The application of Technical Requirement R5

is appropriate where the advice of an Engineeris required

• other specialist advice

• the work necessary to ensure that the buildingmeets the Technical Requirements

• new work which could affect the existing structure.Past performance should not be assumed tosatisfy Technical Requirements R1 to R5 as futuredurability will be a major consideration.





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Procedural flowchart

INITIAL SURVEY INCLUDING DESK TOP STUDY

EXISTING BASEMENT?PROBLEMS IDENTIFIED WITH

- WOOD ROT?- BEETLE INFESTATION?

- STRUCTURE?- CONTAMINATION

- DAMP?- OTHER SPECIALIST

AREAS?

DETAILED

SURVEY

FURTHERINVESTIGATION

REQUIRED?

NHBCASSESSMENT

SATISFACTORY?

FURTHERINVESTIGATION

REQUIRED?

UNFORESEENPROBLEMS?

COMPLETE PROJECT & PROVIDE COPIES OFGUARANTEE/WARRANTY CERTIFICATES TO NHBC

SURVEY REPORTS(S)& APPLICATION

TO NHBCDESIGN WORKSNO

NO

NO

NO

NO

YES

YES

YES

YES

YES

COMMENCEWORKS

NHBC REJECTSSUBMITTED

SCHEME

SPECIALIST

SURVEY(S)

DESIGN SPECIALISTWORKS

ADVISENHBC


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SURVEY OF EXISTING BUILDING

C1 Surveys shall be carried out by

competent and qualified personswith relevant knowledge andexperience, to establish thecurrent condition of the building

The builder should arrange for thorough internal andexternal surveys to assess the condition of the existingbuilding. The causes of any damage or defect shouldbe accurately determined and appropriate remedialwork recommended.

The following surveys will normally be necessary:

• initial survey

• detailed survey• specialist survey(s).The initial survey should include a desktop studyand a walkthrough appraisal of the building.

The detailed survey should be carried out by acompetent and qualified person with relevantknowledge and experience (e.g. an RICS BuildingSurveyor), whose status (including professionalindemnity insurance) is accepted by NHBC.

The specialist survey(s) should be carried out wherethe defect, damage or likely remedial measures areof a specialist nature. Examples include:

• structural waterproofing (tanking) of basements

• wood rot

• beetle infestation

• structure

• contamination

• damp-proofing

• wall tie replacement

• asbestos

•drainage.

The survey(s) should include for appropriateopening up to expose the vulnerable parts of thebuilding. Where, for whatever reason, parts ofthe building are not surveyed, this should be clearlystated in the report(s). Further survey(s) andreport(s) may be required for these parts.

The residual effects of previous use of thebuilding e.g. agriculture / industry, should beestablished by the survey(s) together withdetailed proposals for remediation.

Appendix B provides guidance on items to be

included in the survey(s).

Further guidance on surveying existing buildings isgiven in various Building Research Establishment(BRE) publications including:

• BRE – Assessing traditional housing for rehabilitation

• BRE – Surveyors’ checklist for rehabilitation oftraditional housing.

Appendix A provides details of useful contactsand a list of publications that are relevant toconversions and renovations.

A copy of all survey reports should be madeavailable to NHBC.

DESIGN STANDARD

C2 Design shall meet theTechnical Requirements

New work should be designed in accordance withNHBC Standards.

Conversion and renovation work should be designedin accordance with these Standards for Conversionsand Renovations.

Recommendations contained within the surveyreport(s) should be incorporated in the design.

Copies of planning approvals and consents should bemade available to NHBC upon request. NHBC shouldbe made aware of any planning conditions orrestrictions that could result in a failure to comply withthe Technical Requirements. NHBC will decide on themost appropriate course of action to resolve the matter.In certain cases it may be necessary for NHBC to declineto offer cover for the conversion or renovation.

COMPLETED WORK

C3 Completed work shall meet theTechnical Requirements, take accountof the design and follow establishedgood practice and workmanship

Work should be carried out in accordance withthe design. Recommendations contained withinthe survey report(s) should be implemented.

New work should be carried out in accordance withNHBC Standards.

Conversion and renovation work should be carried outin accordance with these Standards for Conversionsand Renovations.




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BUILDING REGULATIONS

C4 Design and completed work shall

comply with building regulations

INSURED GUARANTEES/WARRANTIES

C5 Proprietary remedial treatmentrelating to wood rot, beetleinfestation, damp-proofing,structural waterproofing(tanking), wall tie replacementand other specialist work shallbe the subject of a suitableinsured guarantee/warranty

Where such work is carried out theguarantee/warranty should:

• be provided by the specialist contractor

• cover any failure of the work

• cover any consequent opening up andmaking good

• remain valid for a minimum period of 20 years

• be in favour of the homeowner (provided

it is automatically transferred at no cost tosubsequent owners) and NHBC.

The specialist contractor’s obligations should becovered by an insurance policy issued by a UKregistered insurer, which includes cover againstthe specialist contractor’s insolvency.

The insurance policy should specify theproperty covered.

WOOD ROT AND

BEETLE INFESTATIONC6 Specialist advice shall be

obtained to identify all sources ofwood rot and beetle infestation,and to recommend a suitablemethod of elimination. Remedialwork shall be carried out takingaccount of the specialist advice

A suitably qualified and experienced surveyorshould carry out surveys for wood rot andbeetle infestation. Acceptable qualificationsinclude CSRT (Certificated Surveyor in Remedial

Treatment) or ASRT (Assessed Surveyor inRemedial Treatment).

Remedial work should:

• be designed by a suitably qualified andexperienced surveyor, and

• be carried out by a competent specialistcontractor approved by NHBC, and

• be the subject of a suitable insuredguarantee/warranty in accordance with Clause C5.

Members of The Property Care Association,a division of the British Wood Preserving andDamp-Proofing Association (BWPDA) backed bythe Guarantee Protection Insurance Ltd meet theabove requirements.

Other surveyors and specialist contractors may beacceptable subject to NHBC’s written acceptance.

Copies of the specialist report detailing the remedialwork and identifying the affected areas, together withcopies of the guarantee/warranty and certificate ofinsurance should be made available to NHBC.

(a) wood rot

The remedial work should ensure that:

• the source of all water and damp ingressis eliminated

• the extent of spread of wood rot is determined

• all rotted wood is removed

• all structurally weakened wood is replacedwith preservative-treated wood or repairedwith a proprietary structural repair resin system.All sawn ends should be treated with afungicide/insecticide preservative

• where rot has been identified, retained woodis treated with preservative in accordance withBS 8417:2003

• any plaster affected by fungi is removed

• any masonry affected by fungi is treated with afungicidal fluid.

(b) beetle infestation

The remedial work should ensure that:

• the treatment is appropriate for the type of woodboring beetle identified

• structurally weakened wood should be replaced bypre-treated wood or repaired with a proprietarystructural repair resin system.

Additional guidance may be obtained from‘Recognising wood rot and insect damage inbuildings’ published by BRE.




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VERMIN AND PEST INFESTATION

C7 Vermin and pest infestation

in the building shall beidentified and eliminated

Where there is evidence of vermin or pest infestation,the extent of the damage should be established andremedial treatment carried out.

The treatment necessary will depend on the typeof vermin or pest. Specialist advice can be obtainedfrom the British Pest Control Association (BPCA).

The remedial work should include preventionmeasures that will reduce the likelihood of re-entry ofthe vermin or pest into the building, its fabric or voids.

FOUNDATIONS

C8 Foundations shall be capableof transmitting existing andproposed loads to the groundwithout excessive movement

New foundations should be designed andcarried out in accordance with NHBC StandardsPart 4 ‘Foundations’.

The condition of the existing foundations andsupporting ground should be assessed as part of the

survey(s), and remedial work carried out as necessaryto provide satisfactory in-service performance for thedesign life of the building.

Items to be taken into account include:

(a) subsidence and settlement

Where the cause of the failure is weak bearingstrata such as peat layers, fill, etc, foundationsshould be strengthened or replaced. This mayinvolve underpinning or other specialist foundationtechniques. Subsidence caused by clay shrinkagemay also necessitate underpinning.

All underpinning and associated foundation workshould be designed and supervised by an Engineeror as required by NHBC.

Subsidence caused by mining or other undergroundworkings will require specialist advice from an Engineer.The Engineer may be required to supervise the workon site.

The potential for differential settlement between new,existing and underpinned foundations/structuresshould be taken into account.

Where leaking drains have caused foundation failurethey should be replaced. Drains that are to be re-laidshould, if possible, be re-routed so that if leakageoccurs again, foundations will not be affected.New work should comply with Chapter 5.3‘Drainage below ground’.

(b) heave

Foundations that have been damaged by clayheave, which occurs when desiccated shrinkable

clay re-hydrates and is commonly associated withmoisture recovery following the removal of trees orvegetation, should be underpinned.

Underpinning should be designed and supervisedby an Engineer or as required by NHBC.Compressible material should be installed as requiredby the design to accommodate movement resultingfrom further clay heave. Refer to NHBC StandardsChapter 4.2 ‘Building near trees’, Chapter 4.4 ‘Stripand Trench fill foundations’ and Chapter 4.5 ‘Raft,pile, pier and beam foundations’, as appropriate.

Foundation design should take account of existing,

removed and proposed planting.

(c) chemical attack

Foundations that have been or could be damagedby high sulfate levels or other aggressive elements inthe soil or ground water, should be repaired orreplaced as directed by an Engineer.

Additional guidance on the concrete grade to ensureadequate durability may be obtained from:

• NHBC Standards Chapter 2.1 ‘Concrete andits reinforcement’

• BS 8500• BS EN 206-1

• BRE Special Digest 1.

(d) frost damage

Damage that has been caused by frost heave insusceptible soils or by ice formation in the pores ofpoorly compacted concrete should be repaired orreplaced as directed by an Engineer. Frost damagenormally occurs to very shallow foundations.

The effect of frost heave can be overcome by

deepening the foundations by underpinning.This should be designed and supervised by anEngineer or as required by NHBC. Defectiveconcrete should be replaced.

(e) adjacent work

Existing foundations that have been damageddue to the proximity or depth of other foundationsor services, should be repaired or replaced asdirected by an Engineer.

New foundations should be designed so as not toadversely affect adjacent foundations.




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FOUNDATIONS

C8 (continued)

(f) underground erosion

Granular subsoils such as sand and gravel maysuffer from erosion of fine particles by movementof ground water leading to subsidence.The introduction of new drains with a granular bedand surround may also take ground water from thesite and could have the same effect on otherwisesound existing foundations. Where this is likely,alternatives should be considered.

(g) changes in loading

The effects of proposed changes to thesuperstructure should be taken into account.The loading on existing foundations may becomeexcessive or unevenly distributed, necessitatingreplacement, underpinning or otherwise improvinginadequate existing foundations.

BASEMENTS AND STRUCTURALWATERPROOFING (TANKING)

C9 All elements (including walls, floors

and foundations) forming a basementshall be suitable for their location

In this Clause the term ‘basement’ meansconstruction which is wholly or partly belowground level and for which normal damp-proofingarrangements are inappropriate.

New basements should be designed and constructedin accordance with NHBC Standards Chapter 5.1‘Substructure and ground bearing floors’.

The condition of existing basements should beassessed as part of the survey(s), and remedialwork carried out as necessary to provide

satisfactory in-service performance for the designlife of the building.

The design should take account of the British CementAssociation Approved Document “Basements fordwellings”. Its principles should be followed inEngland, Wales, Scotland and Northern Ireland.


(a) structural stability

Any alteration, even temporary, to the loading onan existing structurally sound basement may causestructural damage.

An Engineer should design all structural alterationsto basements, such as:

•increasing the height of the retaining walls

• reducing the ability of the floor above to providelateral support to the walls

• lowering floor levels to increase ceiling heights

• alterations to the existing applied loadings

• additional loading from adjacent structures.

(b) control of water and damp ingress

Basements should have adequate resistance tothe passage of water/moisture to the inside.

The design should ensure that the level of

protection against water and moisture reaching theinternal surfaces is appropriate for the proposed use.Where there is any doubt about the use, the level ofprotection required for habitable accommodationshould be provided.

Basements to be used for habitable accommodationshould allow no water penetration and provide a dryenvironment if maintained by adequate heating andventilation. This is referred to as ‘Grade 3’ in the“Basements for dwellings” Approved Document.

Walls and floors to basements to be used for parkingcars, for storage or as plant rooms should allow no

water penetration (unless a type C drained cavity)although moisture vapour is tolerated. This is referredto as ‘Grade 2’ in the “Basements for dwellings”Approved Document.

It should not be assumed that a wall, which is dryat the time of the survey, would not cause a problemat a future date.

Existing basements should be provided with a newstructural waterproofing (tanking) system unless itcan be demonstrated that the existing system willprovide satisfactory in-service performance for thedesign life of the building.

Structural Waterproofing should:

• be designed by a suitably qualified andexperienced specialist surveyor, and

• be carried out by a competent specialist contractorapproved by NHBC, and


Members of the Structural Waterproofing Group,a division of the British Wood Preserving andDamp-proofing Association (BWPDA) backed by theGuarantee Protection Insurance Ltd will meet theabove requirements and therefore be acceptable.




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Where an internal tanking system is used, additionalinternal walling and flooring may be necessary.The effect on room size, especially height, should

be taken into account. The electrical installationshould be on the dry side of the tanking.

Structural waterproofing (tanking) should becontinuous unless designed service inlets areprovided. Fixings should not penetrate the tanking.Tanking should be in accordance with BS 8102,or satisfactorily assessed in accordance withTechnical Requirement R3.

(c) condensation

Adequate provision should be made to prevent surfaceand interstitial condensation within the basement.

The following should be considered:

• appropriate ventilation

• adequate heating

• appropriate insulation

• avoiding cold bridging

• treatment of hygroscopic salts contained in wallsand floors

• removal of water vapour from kitchensand bathrooms.

Further guidance is given in the British Cement

Association Approved Document ‘Basements fordwellings’ and the BRE guide ‘Thermal insulation:avoiding risks’.

DRAINAGE BELOW GROUND

C10 Drainage systems shall convey fouleffluent and rainwater satisfactorilyto an appropriate outfall

Drainage systems should have adequate capacity forthe proposed use of the building and take account of

the number of people who will use it.New drainage should be designed and constructed inaccordance with NHBC Standards Chapter 5.3‘Drainage below ground’.


(a) Existing drainage

Existing drainage should be replaced unless it can bedemonstrated that it will provide satisfactory in-serviceperformance for the design life of the building.

Where it is proposed to retain existing drainage,a thorough survey of the whole system, including

a CCTV survey, should be carried out to establishits current condition, including access points andconnections to main sewers.

The report of the CCTV survey should identifywhich drainage runs require repair or replacement.A copy of the report should be made available

to NHBC.Disused drains should be removed or sealed toprevent the entry of vermin and the possibility offuture collapse.

(b) access

Where the existing drainage system is to be retained,and lengths do not have rodding access in accordancewith current requirements, additional access pointsshould be provided.

(c) inspection chambers, manholes, interceptors,

septic tanks and cesspoolsExisting inspection chambers and manholes may needrebuilding e.g. walls of manholes may need upgradingdue to inadequate structural sufficiency or groundwater ingress etc.

Inspection chambers and manholes locatedwithin habitable parts of the building will notnormally be acceptable.

New covers will be required where existing coversare defective or where chambers will be subject toincreased loading. Locked covers to preventaccidents may be required.

Existing interceptors should normally be removedfrom the drainage system.

NHBC will normally reject any proposal to retainexisting septic tanks or cesspools.

GROUND FLOORS

C11 Ground floors shall have adequatedurability and support and transferloads to the substructure or the groundsafely without undue movement, and

shall resist the passage of moisture,contaminants and gases to the insideof the building

New ground floors should be designed andconstructed in accordance with NHBC StandardsChapters 5.1 ‘Substructure and ground bearingfloors’ or 5.2 ‘Suspended ground floors’.

The condition of existing floors should beassessed as part of the survey(s), and remedialwork carried out as necessary to provide satisfactoryin-service performance for the design life ofthe building.

The effect of any change in loading should be takeninto account. In some cases, e.g. listed buildings,specialist advice may be required.




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GROUND FLOORS

C11 (continued)


(a) ground bearing floors

Ground bearing floors that have suffered damageshould be removed and replaced in accordance withNHBC Standards Chapter 5.1 ‘Substructure andground bearing floors’.

(b) damp-proofing of ground bearing floors

Where existing concrete ground bearing floorsdo not have adequate protection against damp fromthe ground, a new dpm, linked to the dpc should

be provided. It is unlikely that floors laid beforethe mid 1960’s will have adequate protectionagainst damp.

Appropriate dpm materials are listed in NHBCStandards Chapter 5.1 ‘Substructure and groundbearing floors’ (Materials section).

If the existing floor is other than concrete (e.g. flagslaid directly on consolidated sub soil), specialist adviceshould be followed.

(c) suspended timber floors

Where existing timber joists do not have adequateprotection against damp, appropriate damp-proofingwork should be carried out to ensure durability.

Where timber joists built into solid walls areshowing signs of rot (particularly at joist ends),remedial work should be carried out inaccordance with Clause C6.

Joists shown to be inadequate by the survey shouldbe strengthened, strutted, or reduced in span, oradditional joists should be added as appropriate.

The effects of long-term creep deflection shouldbe taken into account.

Joists with excessive notches and/or holes shouldbe replaced or a structural repair carried out.

(d) sub-floor voids

Voids beneath existing timber ground floorsshould be ventilated by openings providing notless than 1500mm2 of open area per metre runof external wall on two opposite sides.

Where the lower surface of the void is belowground level and there are indications of previousflooding, then:

•the level of the void should be raised, providedventilation and durability are not compromised, or

• the void should be drained to an appropriateoutfall, or

• land drains should be provided to the perimeterof the building to prevent the void being flooded.The land drains should be connected to

a suitable outfall.

Any debris beneath the floor likely to createdampness or affect the ventilation should beremoved. Vegetation within the sub-floor voidshould be removed.

Honeycomb sleeper walls, including dpcs,should be repaired if defective.

(e) contaminants and gases

New and existing ground bearing or suspendedground floors should resist the entry of groundcontaminants, radioactive and other toxic orinflammable gases to the inside of the building.

(f) screeds and other finishes

Damaged screeds and other finishes should bereplaced, together with the reinstatement of any dpm.

(g) flooring/decking

New flooring/decking should be in accordance withNHBC Standards Chapter 6.4 ‘Timber and concreteupper floors’.

Unsound or contaminated flooring/decking

should be removed and replaced. Loose boardsshould be re-fixed. The upper surface may beimproved by punching nail heads and sanding.

WALLS - STRUCTURE

C12 Walls shall support and transferloads to the foundations safelyand without undue movement

New walls should be designed and constructed inaccordance with NHBC Standards Part 6‘Superstructure (excluding roofs)’.

The condition of existing walls should be assessed aspart of the survey(s), and remedial work carried outas necessary to provide satisfactory in-serviceperformance for the design life of the building.


(a) cracking

The cause of any cracking, regardless of width,should be identified and addressed. Further guidanceis given in BRE Digests 251 and 361.

Depending on the number and location, cracks up to

1.5mm width in masonry are generally unobtrusive,and provided they are not progressive and will notincrease the possibility of moisture ingress, cannormally be left unattended.




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Cracks over 1.5mm wide in masonry should be cutout and re-stitched to obtain acceptable bondingand appearance. The reconstruction of panels may

be necessary.Where work is necessary the following maybe considered:

• cracked bricks or stone may be removed andreplaced with bricks or stone to match the existing

• cracked joints may be raked out to a depth of15mm and be re-pointed to match the existing

• proprietary crack repair resin productsmay be used in accordance with themanufacturers’ recommendations.

(b) mortarCompatible repointing mortar should be usedas follows:

• for existing mortar of weak to medium strength,mix proportions of 1:1:9 cement:lime:sand shouldbe used

• for stronger existing mortar, mix proportions of1:1:6 cement:lime:sand should be used

• wetting masonry before applying mortar improvesadhesion (alternatively, a water retaining additivemay be used in the mortar)

• where walls are located in areas of severeexposure to wind driven rain, the use of polymeradditives in the mortar will increase bond anddurability (in such cases sand should havenegligible clay content)

• proprietary gun-applied pointing systemsmay be used, in accordance with themanufacturer’s recommendations.

(c) spalling masonry

Where spalling of existing masonry is extensiveand the stability or durability of the wall is adverselyaffected, damaged units should be cut out

and replaced.

It may be possible to cut out and re-use aspalled unit with its sound face showing.Alternatively, adherent colour match compoundsare available but colour may subsequently fade.

Where spalling of existing masonry is limited,damaged units may be retained.

(d) corroded cavity wall ties

Where the extent of corrosion might affect thestability or durability of the wall, one of thefollowing remedial measures should be used:

• demolition and rebuilding of the outer leaf andinstallation of suitable new wall ties assessed inaccordance with Technical Requirement R3

• installing proprietary remedial wall ties assessedin accordance with Technical Requirement R3.This work should:

- be designed by a suitably qualified andexperienced specialist surveyor, and

- be carried out by a competent specialistcontractor approved by NHBC, and

- be the subject of a suitable insuredguarantee/warranty in accordance with Clause C5.

Members of the Property Care Association, a divisionof the British Wood Preserving and Damp-proofingAssociation (BWPDA) backed by the GuaranteeProtection Insurance Ltd will meet the aboverequirements and therefore be acceptable to NHBC.

Other wall tie replacement work may be acceptablesubject to NHBC’s written acceptance.

Old wall ties should be removed if corrosion is severe.In less severe cases, a corrosion protection system maybe acceptable with the redundant ties left in place.

(e) damage caused by sulfate attack

BRICKWORK

Suitable work should be carried out to ensuresources of dampness associated with the sulfateattack are removed. Work could include the repairor replacement of damaged or ineffective copingsand other weathering details.

Where it is necessary to rebuild parts of wallsdamaged by sulfate attack, replacement bricks shouldbe of low soluble salt content (L designation) andmortar should contain sulfate-resisting cement.

NHBC Standards Chapter 6.1 ‘External masonrywalls’ gives guidance on brickwork andmortar specifications.

RENDER

Where render is damaged by sulfate reaction, itshould be replaced with a suitable mix for thebackground (i.e., not stronger than the background)and should contain Sulfate Resisting PortlandCement. The mix should be appropriate to theexposure rating of the wall. For details of suitablerendering mixes, see BS 5262.

(f) lintels

Replacement lintels will be required where:

• existing lintels or their bearings are defective(inadequate bearings should also be made good)

• openings other than brick arches do nothave adequate support (e.g. where masonryis inadequately supported by door andwindow frames)




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WALLS - STRUCTURE

C12 (continued)

(f) lintels (continued)

• existing lintels will be subjected to increasedloading and their ability to carry the increasedload cannot be substantiated.

Timber lintels where required as replacements foraesthetic reasons, should be preservative-treated inaccordance with NHBC Standards Chapter 2.3‘Timber preservation (natural solid timber)’.

(g) embedded timber

Timber embedded within solid masonry can be

retained provided there is no evidence of wood rot,active beetle infestation or other deterioration,and there are no other changes to the exposureconditions of the wall. Preservative treatment islikely to be required.

(h) external ground levels

Levels should be adjusted to ensure the dpc is aminimum of 150mm above ground level.

WALLS – DAMP-PROOFING

C13 Walls shall resist the passage of waterand moisture from the ground

New walls should be designed and constructed inaccordance with NHBC Standards Part 6 ‘Superstructure(excluding roofs)’

The condition of the damp-proofing arrangementsfor existing walls should be assessed as part of thesurvey(s), and remedial work carried out as necessaryto provide satisfactory in-service performance for thedesign life of the building.

It should not be assumed that a wall that is dry at the

time of the survey will not cause a problem at afuture date.

PHYSICAL DAMP-PROOF SYSTEMS

Depending on the existing construction, it may bepossible to install a physical dpc. Installation shouldbe carried out in short lengths. Sheet material dpcs,normally black polyethylene inserted into a cut, areacceptable if adequately lapped. The minimum lapshould be 100mm.

Brick dpcs should consist of two courses of claydpc bricks or clay engineering bricks to BS EN 771-1,laid breaking joint and bedded in a 1:1 / 4:3,cement:lime:sand mortar. Brick dpcs are onlysuitable to resist the upward movement of moisture;they are not suitable to resist the downward orlateral movement of water.

CHEMICAL DAMP-PROOF SYSTEMS

A suitably qualified and experienced surveyorshould carry out surveys for rising dampness.

Acceptable qualifications include CSRT(Certificated Surveyor in Remedial Treatment) orASRT (Assessed Surveyor in Remedial Treatment).

Remedial work should:

• be designed by a suitably qualified andexperienced specialist surveyor, and

• be carried out by a competent specialist contractorapproved by NHBC, and


Members of The Property Care Association, a division

of the British Wood Preserving and Damp-proofingAssociation (BWPDA) backed by the GuaranteeProtection Insurance Ltd meet the aboverequirements.

Other surveyors and specialist contractors may beacceptable subject to NHBC’s written acceptance.

A copy of the survey report should be madeavailable to NHBC.

Chemical dpc systems should have independentcertification in accordance with TechnicalRequirement R3.

To ensure chemical dpcs will function correctly:• chemical dpcs should be installed at the

correct level in relation to the level of anyadjacent floor structure

• in the case of timber ground floors the dpcshould be formed below the level of the joistends. Alternatively the joists should beindependently supported e.g. on hangers orsleeper walls

• chemical dpcs in walls adjacent to solid floorsshould be linked with the floor dpm

• associated re-plastering work should becarried out by the specialist contractor orapproved sub-contractor.

WALLS - WEATHERPROOFING

C14 External walls shall be suitable for theirexposure and resist the passage ofmoisture to the inside of the building

New walls should be designed and constructedin accordance with NHBC Standards Part 6‘Superstructure (excluding roofs)’.




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The condition of existing walls should beassessed as part of the survey(s), and remedialwork carried out as necessary to provide

satisfactory in-service performance for thedesign life of the building.


(a) moisture resistance from outside

Where evidence of water ingress is identified,preventative measures could include:

• installing a proprietary cladding system assessedin accordance with Technical Requirement R3

• applying a render system in accordance with NHBCStandards Chapter 6.1 ‘External masonry walls’

• installing a proprietary insulated render systemthat has been assessed in accordance withTechnical Requirement R3

• re-pointing defective mortar joints

• installing a specialist internal lining system that isnot affected by dampness in the existing wall.

NHBC will not normally accept the use of masonrypaint or the application of surface treatment toimprove moisture resistance.

Attention should be given to openings wherereplacement or additional dpcs and trays may

be required.

Existing lintels with evidence of damppenetration from the outside should be protectedwith a suitable tray.

Where cavity insulation is to be installed,dpc trays are required over all existing openings,irrespective of previous damp penetrationproblems. Further guidance is given in NHBCStandards Chapter 6.1 ‘External masonry walls’.

(b) existing render

Where a crazing pattern of many fine cracks exists butrendering is not loose, the application of a permeable,flexible decorative finish is acceptable. If the cracksextend through the render and the render is hollow,then it should be removed and replaced.

Where over-strong render has curled away fromthe backing, it should be replaced with a suitablemix for the background (i.e. not stronger than thebackground). The mix should be appropriate tothe exposure rating of the wall. For details ofsuitable rendering mixes, see BS 5262.

(c) existing cladding

Any missing, damaged or loose cladding should bereplaced or re-fixed (see Clause C24). Further guidanceis given in NHBC Standards Chapter 6.9 ‘Curtainwalling and cladding’.

(d) timber frame walls

Specialist advice from an Engineer should beobtained where repairs to a timber frame building

are required.

Sources of dampness causing rot should beeliminated before remedial work is carried out.

Guidance is given in NHBC Standards Chapter 6.2‘External timber framed walls’.

(e) parapet walls

New parapet walls should be designed andconstructed in accordance with NHBC StandardsChapter 6.1 ‘External masonry walls’.

Existing parapet walls should be taken down and

re-built unless it can be demonstrated that they arestructurally stable, weathertight and will providesatisfactory in-service performance for the designlife of the building.

Items to be taken into account when assessingthe parapet wall include:

• structural stability

• evidence of water penetration

• that all necessary cappings, copings, dpcs andflashings are present

• that the copings will shed water clear of the wall.The condition of the parapet gutter shouldbe assessed and where necessary, appropriateremedial action carried out to ensure satisfactoryin-service performance.

Where the parapet gutter has an upstand onall sides, an overflow outlet should be provided,through either the parapet or the upstand.The size of the overflow outlet should not be lessthan the size of the rainwater outlet (or outlets ifthere are several).

SEPARATING WALLSC15 Separating walls shall have reasonable

resistance to the passage of sound

New separating walls should be designed andconstructed in accordance with the Building Regulationsand NHBC Standards Chapter 6.3 ‘Internal walls’.

The condition of existing separating wallsshould be assessed as part of the survey(s), andremedial work carried out as necessary to providesatisfactory in-service performance for the designlife of the building.




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SEPARATING WALLS

C15 (continued)


• the construction and condition of existing walls

• the removal of any existing timber or steel lintelsin walls

• adequate making good of previous openingsin walls

• adequate making good of voids and hidden areasin or around walls

• satisfactory support of new and existing walls

•satisfactory sealing of penetrations toaccommodate new or existing services in walls.

CHIMNEYS AND FLUES

C16 Chimneys and flues shall be structurallystable, resistant to the effects of gasesand heat and resistant to the passageof moisture into the building

New chimneys and flues should be designed,constructed and installed in accordance with NHBCStandards Chapter 6.8 ‘Fireplaces, chimneys and flues’.

The condition of existing chimneys and fluesshould be assessed as part of the survey(s), andremedial work carried out as necessary to providesatisfactory in-service performance for the designlife of the building.

The following should be taken into account whenassessing the existing chimney:

• structural stability

• weatherproofing, e.g. that all necessary cappings,copings, dpcs and flashings are present and thatwater is not penetrating the flue or masonry

• that copings will shed water clear of the chimney

• that the existing chimney or flue will achievesatisfactory performance.

Existing chimneys and flues may be unsuitable toserve new appliances either using the same or adifferent fuel. The installation of new appliancesshould comply with statutory requirements.

Where dampness has penetrated to the inside ofthe dwelling through or around the chimney, thecause should be established and necessary workundertaken to prevent recurrence. Particular care

should be taken where a room is to be built withinan existing roof space.

Where existing chimneys and flues are to be retainedbut no longer used they should be fitted with asuitable capping and be ventilated. The effects of

possible sound transmission through the ventilationopenings should be taken into account.

Where chimneys and flues are to be removed,they should be either totally removed or haveany parts that remain adequately supported.

Where existing mortar has eroded, or is crackedor crumbling, it should be raked back to soundmortar. Mortar used for re-pointing shouldnormally be 1:1 / 2:41 / 2, SRPC: lime: sand, withair entraining additive.

Proprietary additives and re-pointing systems should beused in accordance with manufacturers’ instructions.

Where extensive breakdown of the mortar hasoccurred, consideration will need to be given tore-building of the chimney.

Chimney/flue linings should be provided as necessaryto achieve satisfactory in-service performance.

Chimney/flue linings should be in accordance withTechnical Requirement R3 and NHBC StandardsChapter 6.8 ‘Fireplaces, chimneys and flues’.

Existing chimneys in some older buildings maynot be suitable for installation of approved linings.Specialist advice should be sought.

UPPER FLOORS

C17 Upper floors shall have adequatedurability and support and transferloads to the supporting structuresafely without undue movement

New upper floors should be designed andconstructed in accordance with NHBC StandardsChapter 6.4 ‘Timber and concrete upper floors’.

The condition of existing upper floors should be

assessed as part of the survey(s), and remedialwork carried out as necessary to providesatisfactory in-service performance for the designlife of the building.

The effect of any change in loading should be takeninto account.

In some cases, e.g. listed buildings, specialist advicemay be required.


(a) timber upper floors

Where timber joists built into solid walls are showing

signs of rot (particularly at joist ends), remedial workshould be carried out in accordance with Clause C6.




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Inadequate joists should be strutted, reduced in spanor have additional joists added as appropriate.

The effects of long-term creep deflection should betaken into account.

Joists with excessive notches and/or holes should bereplaced or a structural repair carried out.

(b) flooring/decking

New flooring/decking should be in accordance withNHBC Standards Chapter 6.4 ‘Timber and concreteupper floors’.

Unsound or contaminated flooring/decking shouldbe removed and replaced. Loose boards should bere-fixed. The upper surface may be improved by

punching nail heads and sanding.

(c) other floors

Structural alterations should only be carried outon the advice of an Engineer.

(d) screeds and other finishes

Damaged screeds and other finishes shouldbe replaced.

C18 Separating floors shall havereasonable resistance to the

passage of soundNew separating floors should be designed andconstructed in accordance with the BuildingRegulations and NHBC Standards Chapter 6.4‘Timber and concrete upper floors’.

The condition of existing separating floorsshould be assessed as part of the survey(s),and remedial work carried out as necessary toprovide satisfactory in-service performance forthe design life of the building.


•the construction and condition of existing floors

• adequate making good of previous openingsin floors

• adequate making good of voids and hidden areasin or around floors

• satisfactory support of new and existing floors

• satisfactory sealing of penetrations toaccommodate new or existing services in floors.

Remedial work should be in accordance withClause C17.

STAIRCASES, STAIRWAYSAND LANDINGS

C19 Staircases, stairways and landingsshall provide a safe passage for users

New staircases, stairways and landings shouldbe in accordance with NHBC Standards Chapter6.6 ‘Staircases’.

The condition of existing staircases, stairways andlandings should be assessed as part of the survey(s),and remedial work carried out as necessary to providesatisfactory in-service performance for the design lifeof the building.


(a) suitability of existing structure

Staircases and stairways should be suitable for thenew use of the building. Where an existing privatestaircase becomes a common staircase it will besubject to increased design loads. This should be aconsideration in deciding if the existing staircase canbe retained.

Timber staircases that have been in damp conditionsmay be unsound due to rot and should be replaced.

Staircases that are to be retained may requiresuitable repair.

(b) rise and going

The thickness of new screeds and floor finishesshould be taken into account to ensure an equalrise and equal going for all steps in each flight,and where applicable, series of flights.

PITCHED ROOFS

C20 Pitched roof structures shall supportand transfer loads to the supporting

structure without excessive deflection,and resist the passage of rain andsnow to the inside of the building

New pitched roofs should be designed andconstructed in accordance with NHBC StandardsChapter 7.2 ‘Pitched roofs’.

The condition of existing pitched roofs should beassessed as part of the survey(s), and remedialwork carried out as necessary to providesatisfactory in-service performance for thedesign life of the building.




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PITCHED ROOFS

C20 (continued)

Certain roofs e.g. on listed buildings or inconservation areas, may require specialist adviceand appropriate skills.


(a) existing structure

It should not be assumed that roof members that areperforming satisfactorily at the time of the surveywould not cause a problem at a future date.

Changes in structure and loading should be takeninto account. The existing structure should be

strengthened where replacement roof coveringsare heavier than the existing.

Intermediate support should be provided toreduce spans where members would otherwise beover-stressed.

Improved strutting to purlins should be providedwhere the struts are:

• at inadequate centres

• not propped from loadbearing structure

• not braced to prevent movement.Additional support to water tanks should be providedwhere the existing support is inadequate.

Bracing to trussed rafter roofs should be upgradedin accordance with current requirements.

Holding down/restraint strapping should be providedto meet current requirements where it is necessary.

Where wood is showing signs of rot or beetleinfestation, remedial work should be carried out inaccordance with Clause C6.

(b) roof coverings

Existing roof coverings should be removed and

replaced unless it can be demonstrated that theywill perform satisfactorily for the design life ofthe building.

Recovering of roofs over the existing coveringswill not be permitted unless the system has beenspecifically assessed for this purpose in accordancewith Technical Requirement R3.

Where NHBC agrees to an existing roof coveringbeing retained, second hand (re-claimed) slates andtiles may be required for matching. These should onlybe used if they are accepted by NHBC, in accordancewith Technical Requirement R3.

(c) underlay

Where the roof is to have the existing coveringremoved and replaced, a new underlay should be

provided in accordance with NHBC StandardsChapter 7.2 ‘Pitched roofs’. Adequate ventilationshould be provided.

(d) flashings and weatherings

Flashings and weatherings should normally beformed in lead. Guidance is given in “Lead sheet inBuilding” and other material published by the LeadDevelopment Association.

Cement fillets will not normally be accepted asflashings or weatherings.

FLAT ROOFS AND BALCONIES

C21 Flat roof and balcony structuresshall support and transfer loadsto the supporting structurewithout excessive deflection andresist the passage of rain andsnow to the inside of the building

New flat roofs and balconies should be designedand constructed in accordance with NHBC StandardsChapter 7.1 ‘Flat roofs and balconies’.

The condition of existing flat roofs and balconiesshould be assessed as part of the survey(s), andremedial work carried out as necessary to providesatisfactory in-service performance for the designlife of the building.

The use of timber in balconies should be limitedto secondary elements, which in turn are supportedby materials other than timber. Further guidance isgiven in NHBC Standards Chapter 7.1 ‘Flat roofsand balconies’.

Certain roofs and balconies e.g. on listed buildingsor in conservation areas may require specialist advice

and appropriate skills.


(a) existing structure

It should not be assumed that flat roofs orbalconies that are performing satisfactorily at thetime of the survey would not cause a problem ata future date.

Changes in structure and loading, particularlyreplacement roof or balcony coverings, should betaken into account.




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The existing structure should be strengthened wherereplacement roof or balcony coverings are heavierthan the existing.

Existing reinforced concrete or steel flat roof orbalcony structures should be in satisfactory condition.Structural alterations should only be carried out onthe advice of an Engineer.

Intermediate support should be provided to reducespans on timber roofs where members wouldotherwise be overstressed or are excessively deflected.

Upgrading of strutting may be required.Holding down/restraint strapping should be providedto meet current requirements where it is necessary.

Ventilation to cold deck construction should beprovided in accordance with NHBC Standards Chapter7.1 ‘Flat roofs and balconies’ (cold deck constructionis not acceptable in Scotland).

(b) weatherproofing

Correct detailing of the various interfaces,particularly those beneath balcony door openings,will be required to prevent water entering thebuilding. Further guidance is given in NHBCStandards Chapter 7.1 ‘Flat roofs and balconies’.

Existing roof coverings should be removed andreplaced unless it can be demonstrated that theywill perform satisfactorily for the design life of

the building.

Recovering of roofs and balconies over the existingwaterproofing is not generally permitted unless thesystem has been assessed in accordance withTechnical Requirement R3.

Flat roofs and balconies should have postconstruction minimum falls of 1:80, unless the roofcovering and construction has been independentlyassessed to confirm it is acceptable at zero falls.

ROOF DRAINAGE

C22 Roof drainage shall adequately carryrainwater to a suitable outfall

New rainwater drainage systems should beinstalled in accordance with NHBC StandardsChapter 7.1 ‘Flat roofs and balconies’ or Chapter 7.2‘Pitched roofs’.

The condition of the existing roof drainage, includingparapet and other hidden gutters should be assessedas part of the survey(s), and remedial work carriedout as necessary to provide satisfactory in-serviceperformance for the design life of the building.

Existing lead gutters should be reconstructedand re-lined where there is inadequate allowancefor movement.

All roofs (excluding small areas less than 6m2) shouldhave adequate rainwater drainage.

Where rainwater from new roof areas is to beconnected to an existing system, the capacity of thegutters, downpipes and the suitability of the outfallshould be established, and upgraded where necessary.

Where the roof area has an upstand on all sides,adequate drainage and an overflow outlet shouldbe provided, regardless of the size of the roof.The size of the overflow outlet should not be lessthan the size of the rainwater outlet (or outlets ifthere are several).

Existing rainwater downpipes located internallyshould normally be replaced and relocated externally.

FRAMED BUILDINGS -STRUCTURE

C23 The loadbearing structure offramed buildings shall transferloads to the foundations safelyand without excessive movement

Examples of framed buildings include:

• steel frame

• reinforced concrete frame

• timber frame

• oak frame.Framed buildings should be:

• assessed in accordance with TechnicalRequirements R3 and R5, and

• assessed by an Engineer in accordance with advicegiven in:

• CIRIA Report 111• Institution of Structural Engineers Report

‘Appraisal of existing structures’, and

• BRE Digest 366.Where structural alterations are necessary they shouldbe designed by an Engineer.




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FRAMED BUILDINGS -WEATHERPROOFING

C24 The external walls and roofs of framedbuildings shall be suitable for theirexposure and resist the passage ofmoisture to the inside of the building

New curtain walling and cladding systems should bedesigned and installed in accordance with NHBCStandards Chapter 6.9 ‘Curtain walling and cladding’.

New masonry cladding should be in accordancewith NHBC Standards Chapter 6.1 ‘External masonrywalls’ and the Engineer’s design.

Existing curtain walling and cladding systems should

be surveyed by a suitably qualified and experiencedspecialist surveyor.

The survey report should be made available to NHBC.

Remedial work should be carried out as necessary toprovide satisfactory in-service performance.

The following should be taken into account:

• existing cladding systems should normally beremoved before the replacement system is installed

• replacement systems should be fixed tothe structure

•existing masonry cladding should be assessed inaccordance with Clauses C12, C13 and C14

• roofs should be assessed in accordance withClauses C20, C21 and C22.

DOORS, WINDOWSAND GLAZING

C25 Doors, windows and glazingshall ensure satisfactoryin-service performance

New doors, windows and glazing should be designed,specified and installed in accordance with NHBCStandards Chapter 6.7 ‘Doors, windows and glazing’.

The condition of existing doors, windows andglazing should be assessed as part of the survey(s),and remedial work carried out as necessary toprovide satisfactory in-service performance.

Excessively warped or twisted doors and windowsshould be repaired or replaced.

Doors may require upgrading as fire doors,which should be carried out in accordance withan appropriately tested specification.

Door frames may act as integral members ofpartition framing; reinstatement/repair shouldnot reduce structural integrity.


(a) timber doors and windows

Rotten sections should be replaced with durable orpreservative treated timber. A proprietary repairsystem used in accordance with the manufacturer’srecommendations may be an acceptable alternative.

(b) glazing

Insulating glass units should normally be replacedin accordance with NHBC Standards Chapter 6.7‘Doors, windows and glazing’.

Glazing in critical locations should either:

• break safely, or

• be robust or in small panes, or• be permanently protected by suitable guardingLow level openings may require guarding.Special provisions may be necessary if they arealso used for means of escape.

(c) security

Ironmongery to main and secondary access doorsand to windows should be provided in accordancewith NHBC Standards Chapter 6.7 ‘Doors, windowsand glazing’.

JOINERY

C26 Joinery shall provide satisfactoryin-service performance

New joinery should be fitted in accordancewith NHBC Standards Chapter 8.4 ‘Finishingsand fitments’.

The condition of existing joinery should be assessedas part of the survey(s), and remedial work carriedout as necessary to provide satisfactory in-serviceperformance for the design life of the building.


• where the wood is sound, existing picture rails,dado rails, skirtings and architraves may beretained although refixing may be required

• damaged joinery should be repaired or replaced

• reinstatement of existing work should includeappropriate treatment where necessary inaccordance with Clause C6.




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FLOOR, WALL AND CEILINGFINISHES

C27 Workmanship shall providea satisfactory finish

New floor, wall and ceiling finishes should beapplied in accordance with NHBC StandardsChapters 8.2 ‘Wall and ceiling finishes’ and8.3 ‘Floor finishes’.

The condition of existing floor, wall and ceilingfinishes should be assessed as part of the survey(s),and remedial work carried out as necessary to providesatisfactory in-service performance for the design lifeof the building.

The moisture content of external walls, floors andceilings should be taken into account where separateinternal frames and linings are proposed.


(a) linings

Linings and separating frames, with or without avapour control layer, should only be applied to a dryand stable background.

Adhesive dabs should not be used for fixing toexisting solid walls.

(b) existing wall and ceiling finishesWhere existing backgrounds are to be retained theyshould be sound and provide an adequate backingfor the proposed finish.

Plaster that is not keyed should be replaced orpatched where practicable.

SERVICES – WATER

C28 Every home shall have an adequatehot and cold water supply

New hot and cold water services should be installedin accordance with NHBC Standards Chapter 8.1‘Internal services’.

Existing hot and cold water services should normallybe replaced.

The size and condition of the existing supply shouldbe assessed as part of the survey(s), and upgradedas necessary to provide satisfactory in-serviceperformance for the design life of the building.

SERVICES – ELECTRICAL

C29 Every home shall have an adequate

and safe electrical installationNew electrical services should be installed inaccordance with NHBC Standards Chapter 8.1‘Internal services’.

Existing electrical installations should normally bereplaced unless it can be demonstrated that they arein a safe working condition and have a reasonablelife expectancy.

All electrical installations should comply withBS 7671 formerly the Institution of ElectricalEngineers (IEE) Wiring Regulations current at thetime of the conversion or renovation.

Socket outlets which might reasonably be used tosupply power to external appliances should beprotected by a residual current device (RCD).

To meet with this regulation, all power circuitssupplying sockets should be protected by a residualcurrent device to BS 4293.

Lighting circuits and those supplying power to smokedetectors should not be protected by a residualcurrent device.

The provision of socket outlets, lighting andtelevision reception should be in accordance with

NHBC Standards Chapter 8.1 ‘Internal services’.

SERVICES – GAS

C30 Where provided, gas servicesshall be in accordance withcurrent standards and codes

New gas services should be installed in accordancewith NHBC Standards Chapter 8.1 ‘Internal services’.

All gas services should comply with the Gas Safety(Installation and use) Regulations current at the time

of the conversion or renovation.Existing gas services should normally be replaced.

SERVICES – SPACE HEATING

C31 Where provided, space heatingshall be in accordance with buildingregulations, standards and codes

New systems should be installed in accordance withNHBC Standards Chapter 8.1 ‘Internal services’.

Existing heating systems should normally be replaced

unless it can be demonstrated that they comply withNHBC Standards Chapter 8.1 ’Internal services’ andare in a safe working condition with a reasonablelife expectancy.




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SERVICES – VENTILATION

C32 Homes shall be adequately ventilated

All existing habitable rooms, kitchens and bathroomswithin a home, and common parts in flats, should beprovided with ventilation, which substantially meetswith building regulations applicable to new build.

New extract fan systems should be installed inaccordance with NHBC Standards Chapter 8.1‘Internal services’.

SERVICES – ABOVEGROUND DRAINAGE

C33 Above ground drainagesystems shall ensure satisfactoryin-service performance

New above ground soil and waste systems shouldbe installed in accordance with NHBC StandardsChapter 8.1 ‘Internal services’.

The condition of the existing soil and wastesystem should be assessed and tested as part ofthe survey(s), and remedial work carried out asnecessary to provide satisfactory in-serviceperformance for the design life of the building.

Existing systems to be retained or extended shouldsubstantially meet with current requirements.

PAINTING AND DECORATING

C34 Paint and decorative systems shallprovide an acceptable finish

New and existing work should be thoroughlycleaned down, prepared and a new finish appliedin accordance with NHBC Standards Chapter 8.5‘Painting and decorating’.

Where necessary timber doors and windowsshould be stripped before redecoration.

Metal doors and windows should be strippedbefore redecoration.

Decoration should allow walls to ‘breathe’ so thatvapour pressure does not build up behind the surface.

EXTERNAL WORKS - ACCESS

C35 Adequate access shall beprovided to and around the home

Access, including private roads, shared private drives,private drives, car parking areas and paths, shouldnormally be provided in accordance with NHBCStandards Chapter 9.2 ‘Drives, paths and landscaping’.

The condition of the existing access should beassessed as part of the survey(s), and remedialwork carried out as necessary to provide

satisfactory in-service performance for thedesign life of the building.

EXTERNAL WORKS – GARAGESAND OUTBUILDINGS

C36 Garages and convertedoutbuildings shall be suitablefor their intended purposes

New garages should be designed andconstructed in accordance with NHBC Standards

Chapter 9.1 ‘Garages’.The condition of existing garages and outbuildingsshould be assessed as part of the survey(s),and remedial work carried out as necessary toprovide satisfactory in-service performance for theirintended purpose for the design life of the building.

Outbuildings converted into garages shouldmeet the requirements of NHBC Standards Chapter9.1 ‘Garages’.

In accordance with requirements for new garages,walls to converted garages do not normally needto be totally weather resistant and floors do not

normally require a damp proof membrane.

EXTERNAL WORKS –FREESTANDING WALLS ANDRETAINING STRUCTURES

C37 Freestanding walls and retainingstructures shall be adequate fortheir intended purpose

New freestanding walls and retaining structures

should be designed and constructed in accordancewith NHBC Standards Chapter 9.2 ‘Drives, pathsand landscaping’.

The condition of existing freestanding walls andretaining structures should be assessed as part ofthe survey(s), and remedial work carried out asnecessary to provide satisfactory in-serviceperformance for the design life of the building.


• the stability of the wall or structure, andproposed loading

• assessment of damage or deterioration• that the wall or structure has all the necessarycappings, copings and dpcs

• that the copings shed water clear of the wall.




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EXTERNAL WORKS –GARDEN AREAS(up to 20m from the habitable parts of the home)

C38 Garden areas shall be stable andadequately prepared for cultivation

Work should be carried out in accordance withNHBC Standards Chapter 9.2 ‘Drives, pathsand landscaping’.


• construction rubbish and debris should beremoved from garden and other areas aroundthe home

• old foundations, concrete bases and similarobstructions occurring within 300mm of thefinished ground surface should be removed

• any ground disturbed during the conversion orrenovation works should be re-graded to conformto the general shape of the adjacent ground

• subsoil should not be placed over topsoil and anytopsoil disturbed should be reinstated

• garden areas should be provided with topsoil to athickness of not less than 100mm

• the topsoil should not contain contaminantswhich are likely to present a hazard to users ofthe garden

• waterlogging of the ground around the home,up to a maximum 3.0m from the habitableparts, should be prevented by drainage or othersuitable means.

EXTERNAL WORKS –LANDSCAPING

C39 Possible future damage to the homecaused by planting shall be minimised

Works should be carried out in accordancewith NHBC Standards Chapter 9.2 ‘Drives, pathsand landscaping’.

Where trees or shrubs have been removed, areto be retained or are to be planted by the builder,precautions should be taken to reduce the risk offuture damage to homes and services.

Further guidance is given in NHBC StandardsChapter 4.2 ‘Building near trees’.

PROVISION OF INFORMATION

C40 Designs and specifications

shall be produced in a clearlyunderstandable format andinclude all relevant information

All relevant information relating to the conversionor renovation should be stated clearly andunambiguously, and be readily available.

C41 All relevant information shall bedistributed to appropriate personnel

The design and specification should be madeavailable to all appropriate personnel including sitesupervisors and relevant specialists, sub contractors

and/or suppliers.




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APPENDIX A

Useful contactsAssociation of British Insurers (ABI)

www.abi.org.uk

British Wood Preserving and Damp-proofing Association (BWPDA)

www.bwpda.co.uk

British Pest Control Association (BPCA)

www.bpca.org.uk

Building Research Establishment (BRE)

www.bre.co.uk

Centre for Window and Cladding Technology (CWCT)

www.cwct.org.uk

Construction Industry Research and Information Association (CIRIA)

www.ciria.org

English Heritage

www. english-heritage.org.uk

Environment Agency

www.environment-agency.gov.uk

Guarantee Protection Insurance Ltd (GPIC)www.gptprotection.co.uk

Institute of Historic Building Conservation (IHBC)

www.ihbc.org.uk

Royal Institution of Chartered Surveyors (RICS)

www.rics.org

The Institution of Structural Engineers

www.IstructE.org.uk

Timber Research and Development Association (TRADA)

www.trada.co.uk


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APPENDIX A

Useful publicationsBRE GBG 6 Outline guide to assessment of traditional housing for rehabilitation

BRE Digest 366 Structural appraisal of existing buildings for change of useISE Report Appraisal of Existing Structures

BRE Report 167 Assessing traditional housing