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STANDARDSfor

Conversions and renovations

April 2005 editionEffective from July 2005

Conversions and Renovations

CONTENTS Clause Page

INTRODUCTION 1Technical 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 structural waterproofing (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 AUseful contacts and relevant publications 24

APPENDIX BSurvey(s) of existing buildings 26

Introduction NHBC Standards for Conversions and RenovationsEffective: July 2005 April 2005 edition

INTRODUCTION


PURPOSEThe Standards for Conversions and Renovationsprovide guidance on the type of project that will be acceptable to NHBC, the scope of the survey(s)and work that will be required.

WHAT ARE ‘CONVERSIONS AND RENOVATIONS’?Conversions and renovations are projects that involve work to existing buildings or parts of existing 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 an existing 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 accordance with 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 for the 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 or not they are located in parts of the building coveredby the reports or NHBC’s specific requirements.

TECHNICAL REQUIREMENTSThe Technical Requirements are printed in red. They are mandatory and MUST be met by the builder.

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

Technical Requirement R6 relates specifically to the Standards for Conversions and Renovations.

PERFORMANCE STANDARDSThe 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 the standard achieved is not lower than the stated Performance 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.

INTERPRETATIONOccasionally 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 31April 2005 edition Effective: July 2005

INTRODUCTION


TESTINGTo establish whether the existing building or parts ofit 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 may be required to obtain the services of a specialist todetermine them.

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

STANDARDS, CODES OFPRACTICE AND OTHERAUTHORITATIVE DOCUMENTSWhere the Standards for Conversions andRenovations refer to:

• NHBC Standards

• European Standards

• British Standards

• Codes of Practice

• Authoritative documents or

• Technical approval certification

the 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 NHBC will consider recommendations from otherauthoritative organisations.

LIMITATIONS ON USEThe 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 RenovationsEffective: July 2005 April 2005 edition

INTRODUCTION


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

In England, Wales and the Isle of Man, NHBC will generally accept work that accords with the relevant Approved Documents and their supporting documents. Exceptions would be where NHBC has a higher standard or where there is doubt as to whether the recommendation in the Approved Document is appropriate to aparticular application.

In Scotland and Northern Ireland, account shall be taken of the relevant Building Standards and Regulations.

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

NHBC Standards do not apply to:

• health and safety matters relating to building operations

• handling and use of certain building materials

• planning matters.

R2 Design requirementDesign and specification shall provide 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 in the 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 life of at least 60 years. Individual components andassemblies, not integral to the structure, may have a lesser durability and need planned maintenance,repair or replacement during that period.

Proper account shall be taken of the use and location of materials, products and building systems in relation to:

• durability of both the structure and individual 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 FOR CRITICAL FUNCTIONSFunctions critical to performance are: structure, fire resistance, weatherproofing,durability, thermal and sound insulation, services including heating appliances and flues.


TECHNICAL REQUIREMENTS



R3 (continued)Any of the following are acceptable:

(i) performance in accordance with standards set 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 they are used in accordance with the relevant Code of Practice,or(iii) compliance with standards not lower than those defined in a relevant British Standardspecification or equivalent, provided their use 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 to the Construction Products Directive,or(v) use of materials and products in accordance with well established satisfactory custom andpractice, provided that such custom and practice is acceptable to NHBC,or(vi) acceptance, in writing, by NHBC that the quality and use is satisfactory.

(b) MATERIALS AND PRODUCTS USED FOR NON-CRITICAL FUNCTIONSCompliance with the above acceptance criteria 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).

NoteEquivalents to British Standards or technical approvalsauthority shall be those accepted in the UK.

R4 Workmanship requirementAll work shall be carried out in aproper, neat and workmanlike manner

The Builder shall ensure that:

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

(b) appropriate precautions are taken to prevent 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 during construction (including excessive heat, cold, wetting or drying)

(vi) protection against damage by following trades.

R5 Structural design requirementStructural design shall be carried out by suitably qualified persons in accordance with British Standards and Codes of Practice

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

(a) foundations on hazardous ground where the hazard 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 every building over three storeys in height

(c) certain types of foundations and retaining walls,as required in the individual Chapters of the NHBC Standards

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

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

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




The structural design shall take account of thedurability requirement in Technical Requirement R3 Materials requirement.

In England, Wales, Northern Ireland and the Isle of Man, structural design may be undertaken by 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 Engineer or by a Consulting Engineer employed by the Builder to ensure that the site investigation, choice of foundations, siting and construction of dwellings are properly taken into account and that the design is appropriate for the loading and conditions.

In Scotland, the Engineer shall be independent of the 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 with BS 8103 ‘Structural design of low rise buildings’ will be acceptable.

The Builder shall:

• require the Engineer to issue clear instructions for site personnel

• not permit departure from the design without the Engineer’s written consent

• require the Engineer or his representative to carry out such inspections as may be required by 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 designed under this Technical Requirement, or

(ii) when specifically required by NHBC in these 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, calculations and 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 renovationsExisting buildings shall be surveyed to determine their condition and thework required to bring them into adurable 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 suitability of the existing structure and/or materials

• the structural condition of the existing building and the effect of the proposed conversion and renovation works. The application of Technical Requirement R5 is appropriate where the advice of an Engineer is 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 to satisfy Technical Requirements R1 to R5 as futuredurability will be a major consideration.





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?

NHBC ASSESSMENT

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

SPECIALISTSURVEY(S)

DESIGN SPECIALISTWORKS

ADVISENHBC


SURVEY OF EXISTING BUILDINGC1 Surveys shall be carried out by

competent and qualified persons with relevant knowledge andexperience, to establish the current 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 study and 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 are of 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 appropriate opening up to expose the vulnerable parts of thebuilding. Where, for whatever reason, parts of the building are not surveyed, this should be clearlystated in the report(s). Further survey(s) and report(s) may be required for these parts.

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

Appendix B provides guidance on items to beincluded 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 contacts and a list of publications that are relevant toconversions and renovations.

A copy of all survey reports should be made available to NHBC.

DESIGN STANDARDC2 Design shall meet the

Technical 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 should be 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 WORKC3 Completed work shall meet the

Technical Requirements, take accountof the design and follow establishedgood practice and workmanship

Work should be carried out in accordance with the design. Recommendations contained within the 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.



BUILDING REGULATIONSC4 Design and completed work shall

comply with building regulations

INSURED GUARANTEES/WARRANTIESC5 Proprietary remedial treatment

relating to wood rot, beetleinfestation, damp-proofing, structural waterproofing (tanking), wall tie replacement and other specialist work shall be the subject of a suitable insured 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 and making 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 against the specialist contractor’s insolvency.

The insurance policy should specify the property covered.

WOOD ROT AND BEETLE INFESTATIONC6 Specialist advice shall be

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

A suitably qualified and experienced surveyor should carry out surveys for wood rot and beetle infestation. Acceptable qualifications include CSRT (Certificated Surveyor in RemedialTreatment) or ASRT (Assessed Surveyor in Remedial Treatment).

Remedial work should:

• be designed by a suitably qualified andexperienced surveyor, and

• be carried out by a competent specialist contractor 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 and Damp-Proofing Association (BWPDA) backed by the 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 rotThe remedial work should ensure that:

• the source of all water and damp ingress is eliminated

• the extent of spread of wood rot is determined

• all rotted wood is removed

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

• where rot has been identified, retained wood is treated with preservative in accordance with BS 8417:2003

• any plaster affected by fungi is removed

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

(b) beetle infestationThe 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 in buildings’ published by BRE.



VERMIN AND PEST INFESTATIONC7 Vermin and pest infestation

in the building shall be identified 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 type of 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.

FOUNDATIONSC8 Foundations shall be capable

of transmitting existing and proposed loads to the ground without excessive movement

New foundations should be designed and carried out in accordance with NHBC Standards Part 4 ‘Foundations’.

The condition of the existing foundations andsupporting ground 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.

Items to be taken into account include:

(a) subsidence and settlementWhere the cause of the failure is weak bearing strata such as peat layers, fill, etc, foundations should be strengthened or replaced. This may involve underpinning or other specialist foundationtechniques. Subsidence caused by clay shrinkage may also necessitate underpinning.

All underpinning and associated foundation workshould be designed and supervised by an Engineer or 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) heaveFoundations that have been damaged by clay heave, which occurs when desiccated shrinkable clay re-hydrates and is commonly associated with moisture recovery following the removal of trees orvegetation, should be underpinned.

Underpinning should be designed and supervised by 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 attackFoundations that have been or could be damaged by 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 and its reinforcement’

• BS 8500

• BS EN 206-1

• BRE Special Digest 1.

(d) frost damageDamage 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 bydeepening the foundations by underpinning. This should be designed and supervised by anEngineer or as required by NHBC. Defective concrete should be replaced.

(e) adjacent workExisting foundations that have been damaged due to the proximity or depth of other foundations or services, should be repaired or replaced as directed by an Engineer.

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



FOUNDATIONSC8 (continued)

(f) underground erosionGranular subsoils such as sand and gravel may suffer from erosion of fine particles by movement of 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 loadingThe effects of proposed changes to the superstructure 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 below ground 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 remedial work carried out as necessary to provide satisfactory in-service performance for the design life 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 stabilityAny alteration, even temporary, to the loading on an existing structurally sound basement may causestructural damage.

An Engineer should design all structural alterations to 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 ingressBasements should have adequate resistance to the 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 nowater 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 dry at 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 and Damp-proofing Association (BWPDA) backed by theGuarantee Protection Insurance Ltd will meet theabove requirements and therefore be acceptable.



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 with Technical Requirement R3.

(c) condensationAdequate 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 kitchens and bathrooms.

Further guidance is given in the British CementAssociation Approved Document ‘Basements fordwellings’ and the BRE guide ‘Thermal insulation:avoiding risks’.

DRAINAGE BELOW GROUNDC10 Drainage systems shall convey foul

effluent and rainwater satisfactorily to an appropriate outfall

Drainage systems should have adequate capacity forthe proposed use of the building and take account ofthe 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 drainageExisting 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 establish its current condition, including access points andconnections to main sewers.

The report of the CCTV survey should identify which 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) accessWhere 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 cesspools

Existing 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 located within habitable parts of the building will notnormally be acceptable.

New covers will be required where existing covers are defective or where chambers will be subject toincreased loading. Locked covers to prevent accidents 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 FLOORSC11 Ground floors shall have adequate

durability and support and transferloads to the substructure or the groundsafely without undue movement, andshall 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 be assessed as part of the survey(s), and remedial work carried out as necessary to provide satisfactoryin-service performance for the design life of the building.

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



GROUND FLOORSC11 (continued)


(a) ground bearing floorsGround 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 floorsWhere existing concrete ground bearing floors do not have adequate protection against damp fromthe ground, a new dpm, linked to the dpc should be provided. It is unlikely that floors laid before the mid 1960’s will have adequate protection against 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 floorsWhere 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 are showing signs of rot (particularly at joist ends),remedial work should be carried out in accordance with Clause C6.

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

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

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

(d) sub-floor voidsVoids beneath existing timber ground floors should be ventilated by openings providing not less than 1500mm2 of open area per metre run of external wall on two opposite sides.

Where the lower surface of the void is below ground 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 perimeter of 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 create dampness or affect the ventilation should be removed. Vegetation within the sub-floor void should be removed.

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

(e) contaminants and gasesNew 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 finishesDamaged screeds and other finishes should bereplaced, together with the reinstatement of any dpm.

(g) flooring/deckingNew 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 - STRUCTUREC12 Walls shall support and transfer

loads to the foundations safely and 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) crackingThe 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 to1.5mm width in masonry are generally unobtrusive,and provided they are not progressive and will notincrease the possibility of moisture ingress, cannormally be left unattended.



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

Where work is necessary the following may be 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 products may be used in accordance with themanufacturers’ recommendations.

(b) mortarCompatible repointing mortar should be used as 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 severe exposure to wind driven rain, the use of polymeradditives in the mortar will increase bond anddurability (in such cases sand should have negligible clay content)

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

(c) spalling masonryWhere spalling of existing masonry is extensive and 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 a spalled unit with its sound face showing.Alternatively, adherent colour match compounds are available but colour may subsequently fade.

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

(d) corroded cavity wall tiesWhere the extent of corrosion might affect thestability or durability of the wall, one of the following 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 assessed in 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

BRICKWORKSuitable work should be carried out to ensure sources of dampness associated with the sulfateattack are removed. Work could include the repair or 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 masonry walls’ gives guidance on brickwork and mortar specifications.

RENDERWhere 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) lintelsReplacement 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 not have adequate support (e.g. where masonry is inadequately supported by door and window frames)



WALLS - STRUCTUREC12 (continued)

(f) lintels (continued)

• existing lintels will be subjected to increasedloading and their ability to carry the increased load 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 timberTimber embedded within solid masonry can beretained 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 is likely to be required.

(h) external ground levelsLevels should be adjusted to ensure the dpc is aminimum of 150mm above ground level.

WALLS – DAMP-PROOFINGC13 Walls shall resist the passage of water

and 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 arrangements for 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 thetime of the survey will not cause a problem at afuture date.

PHYSICAL DAMP-PROOF SYSTEMSDepending 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 clay dpc 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 only suitable to resist the upward movement of moisture;they are not suitable to resist the downward or lateral movement of water.

CHEMICAL DAMP-PROOF SYSTEMSA suitably qualified and experienced surveyor should 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 divisionof 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 made available 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 any adjacent floor structure

• in the case of timber ground floors the dpc should be formed below the level of the joist ends. 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 be carried out by the specialist contractor or approved sub-contractor.

WALLS - WEATHERPROOFINGC14 External walls shall be suitable for their

exposure and resist the passage ofmoisture to the inside of the building

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



The condition of existing walls should be assessed as part of the survey(s), and remedial work carried out as necessary to provide satisfactory in-service performance for the design life of the building.


(a) moisture resistance from outsideWhere evidence of water ingress is identified,preventative measures could include:

• installing a proprietary cladding system assessed in accordance with Technical Requirement R3

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

• installing a proprietary insulated render system that 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 damp penetration 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 penetration problems. Further guidance is given in NHBCStandards Chapter 6.1 ‘External masonry walls’.

(b) existing renderWhere 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 from the backing, it should be replaced with a suitable mix for the background (i.e. not stronger than thebackground). The mix should be appropriate to the exposure rating of the wall. For details of suitable rendering mixes, see BS 5262.

(c) existing claddingAny 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 wallsSpecialist advice from an Engineer should be obtained 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 wallsNew 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 design life of the building.

Items to be taken into account when assessing the 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 should be assessed and where necessary, appropriateremedial action carried out to ensure satisfactory in-service performance.

Where the parapet gutter has an upstand on all 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 walls should be assessed as part of the survey(s), andremedial work carried out as necessary to provide satisfactory in-service performance for the design life of the building.



SEPARATING WALLSC15 (continued)


• the construction and condition of existing walls

• the removal of any existing timber or steel lintels in walls

• adequate making good of previous openings in 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 FLUESC16 Chimneys and flues shall be structurally

stable, 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 flues should be assessed as part of the survey(s), andremedial work carried out as necessary to providesatisfactory in-service performance for the design life 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 of the dwelling through or around the chimney, thecause should be established and necessary workundertaken to prevent recurrence. Particular careshould be taken where a room is to be built within an 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 ofpossible 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 have any parts that remain adequately supported.

Where existing mortar has eroded, or is cracked or crumbling, it should be raked back to soundmortar. Mortar used for re-pointing should normally be 1:1/2:41/2, SRPC: lime: sand, with air 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 to re-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 may not be suitable for installation of approved linings.Specialist advice should be sought.

UPPER FLOORSC17 Upper floors shall have adequate

durability 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 beassessed as part of the survey(s), and remedial work carried out as necessary to provide satisfactory in-service performance for the design life 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 floorsWhere timber joists built into solid walls are showingsigns of rot (particularly at joist ends), remedial workshould be carried out in accordance with Clause C6.



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/deckingNew 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 boards should be re-fixed. The upper surface may be improved bypunching nail heads and sanding.

(c) other floorsStructural alterations should only be carried out on the advice of an Engineer.

(d) screeds and other finishesDamaged screeds and other finishes should be replaced.

C18 Separating floors shall havereasonable resistance to the passage of sound

New 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 floors should be assessed as part of the survey(s), and remedial work carried out as necessary to provide satisfactory in-service performance for the design life of the building.


• the construction and condition of existing floors

• adequate making good of previous openings in 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 with Clause C17.

STAIRCASES, STAIRWAYS AND LANDINGSC19 Staircases, stairways and landings

shall provide a safe passage for users

New staircases, stairways and landings should be in accordance with NHBC Standards Chapter 6.6 ‘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 structureStaircases 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 require suitable repair.

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

PITCHED ROOFSC20 Pitched roof structures shall support

and transfer loads to the supportingstructure 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 remedial work carried out as necessary to provide satisfactory in-service performance for the design life of the building.



PITCHED ROOFSC20 (continued)

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


(a) existing structureIt 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 bestrengthened where replacement roof coverings are heavier than the existing.

Intermediate support should be provided to reduce 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 upgraded in 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 coveringsExisting roof coverings should be removed andreplaced unless it can be demonstrated that they will perform satisfactorily for the design life of the building.

Recovering of roofs over the existing coverings will 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) underlayWhere the roof is to have the existing coveringremoved and replaced, a new underlay should beprovided in accordance with NHBC Standards Chapter 7.2 ‘Pitched roofs’. Adequate ventilationshould be provided.

(d) flashings and weatheringsFlashings and weatherings should normally be formed 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 BALCONIESC21 Flat roof and balcony structures

shall support and transfer loads to the supporting structure without excessive deflection and resist the passage of rain and snow to the inside of the building

New flat roofs and balconies should be designed and 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 design life of the building.

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

Certain roofs and balconies e.g. on listed buildings or in conservation areas may require specialist adviceand appropriate skills.


(a) existing structureIt should not be assumed that flat roofs or balconies that are performing satisfactorily at the time of the survey would not cause a problem at a future date.

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



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

Existing roof coverings should be removed andreplaced unless it can be demonstrated that they will 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 DRAINAGEC22 Roof drainage shall adequately carry

rainwater to a suitable outfall

New rainwater drainage systems should be installed in accordance with NHBC Standards Chapter 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 reconstructed and re-lined where there is inadequate allowance for 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 should be provided, regardless of the size of the roof. The size of the overflow outlet should not be less than the size of the rainwater outlet (or outlets ifthere are several).

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

FRAMED BUILDINGS -STRUCTUREC23 The loadbearing structure of

framed buildings shall transfer loads to the foundations safely and 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.



FRAMED BUILDINGS -WEATHERPROOFINGC24 The external walls and roofs of framed

buildings 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 accordance with NHBC Standards Chapter 6.1 ‘External masonrywalls’ and the Engineer’s design.

Existing curtain walling and cladding systems shouldbe 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 to the 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, WINDOWS AND GLAZINGC25 Doors, windows and glazing

shall ensure satisfactory in-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 and glazing should be assessed as part of the survey(s),and remedial work carried out as necessary to provide 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 with an appropriately tested specification.

Door frames may act as integral members of partition framing; reinstatement/repair should not reduce structural integrity.


(a) timber doors and windowsRotten 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) glazingInsulating glass units should normally be replaced in 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 guarding

Low level openings may require guarding. Special provisions may be necessary if they are also used for means of escape.

(c) securityIronmongery to main and secondary access doors and to windows should be provided in accordancewith NHBC Standards Chapter 6.7 ‘Doors, windowsand glazing’.

JOINERYC26 Joinery shall provide satisfactory

in-service performance

New joinery should be fitted in accordance with NHBC Standards Chapter 8.4 ‘Finishings and 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.



FLOOR, WALL AND CEILINGFINISHESC27 Workmanship shall provide

a satisfactory finish

New floor, wall and ceiling finishes should be applied in accordance with NHBC Standards Chapters 8.2 ‘Wall and ceiling finishes’ and 8.3 ‘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) liningsLinings 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 – WATERC28 Every home shall have an adequate

hot 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 upgraded as necessary to provide satisfactory in-serviceperformance for the design life of the building.

SERVICES – ELECTRICALC29 Every home shall have an adequate

and safe electrical installation

New 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 reasonable life expectancy.

All electrical installations should comply with BS 7671 formerly the Institution of ElectricalEngineers (IEE) Wiring Regulations current at the time 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 and television reception should be in accordance withNHBC Standards Chapter 8.1 ‘Internal services’.

SERVICES – GASC30 Where provided, gas services

shall be in accordance with current 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 timeof the conversion or renovation.

Existing gas services should normally be replaced.

SERVICES – SPACE HEATINGC31 Where provided, space heating

shall 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 replacedunless it can be demonstrated that they comply withNHBC Standards Chapter 8.1 ’Internal services’ andare in a safe working condition with a reasonable life expectancy.



SERVICES – VENTILATIONC32 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 – ABOVE GROUND DRAINAGEC33 Above ground drainage

systems shall ensure satisfactory in-service performance

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

The condition of the existing soil and waste system should be assessed and tested as part of the 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 DECORATINGC34 Paint and decorative systems shall

provide an acceptable finish

New and existing work should be thoroughly cleaned down, prepared and a new finish applied in accordance with NHBC Standards Chapter 8.5‘Painting and decorating’.

Where necessary timber doors and windows should be stripped before redecoration.

Metal doors and windows should be stripped before redecoration.

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

EXTERNAL WORKS - ACCESSC35 Adequate access shall be

provided 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 remedial work carried out as necessary to provide satisfactory in-service performance for the design life of the building.

EXTERNAL WORKS – GARAGESAND OUTBUILDINGSC36 Garages and converted

outbuildings shall be suitable for their intended purposes

New garages should be designed and constructed in accordance with NHBC StandardsChapter 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 to provide satisfactory in-service performance for theirintended purpose for the design life of the building.

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

In accordance with requirements for new garages,walls to converted garages do not normally need to be totally weather resistant and floors do notnormally require a damp proof membrane.

EXTERNAL WORKS –FREESTANDING WALLS ANDRETAINING STRUCTURESC37 Freestanding walls and retaining

structures shall be adequate for their intended purpose

New freestanding walls and retaining structuresshould be designed and constructed in accordancewith NHBC Standards Chapter 9.2 ‘Drives, paths and landscaping’.

The condition of existing freestanding walls andretaining structures should be assessed as part of the 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, and proposed 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.



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 with NHBC Standards Chapter 9.2 ‘Drives, paths and landscaping’.


• construction rubbish and debris should be removed from garden and other areas around the 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 contaminants which are likely to present a hazard to users of the garden

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

EXTERNAL WORKS –LANDSCAPINGC39 Possible future damage to the home

caused by planting shall be minimised

Works should be carried out in accordance with NHBC Standards Chapter 9.2 ‘Drives, paths and landscaping’.

Where trees or shrubs have been removed, are to 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 Standards Chapter 4.2 ‘Building near trees’.

PROVISION OF INFORMATIONC40 Designs and specifications

shall be produced in a clearlyunderstandable format and include all relevant information

All relevant information relating to the conversion or 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 contractorsand/or suppliers.




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 Heritagewww. english-heritage.org.uk

Environment Agencywww.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 Engineerswww.IstructE.org.uk

Timber Research and Development Association (TRADA)www.trada.co.uk



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 use

ISE Report Appraisal of Existing Structures

BRE Report 167 Assessing traditional housing for rehabilitation

BRE Report 168 Surveyor’s checklist for rehabilitation of traditional housing

BRE Digest 251 Assessment of damage in low-rise buildings

BRE Digest 343 Simple measuring and monitoring of movement in low-rise buildings - Part 1

BRE Digest 344 Simple measuring and monitoring of movement in low-rise buildings - Part 2

BRE Digest 361 Why do buildings crack?

BRE Subsidence damage to domestic buildings

BRE Report 453 Recognising wood rot and insect damage in buildings

BRE DAS 103 Wood floors : reducing risk of recurrent dry rot

BRE DAS 74 Suspended timber ground floors : repairing rotted joists

BRE Special 1 Concrete in aggressive ground - Parts 1 to 4Digest

BRE Digest 444 Parts 1, 2 & 3 - Corrosion of steel in concrete

BRE Digest 352 Underpinning

BRE Report 447 Brownfield sites - ground related risks for buildings

DETR Asbestos and man made mineral fibres in buildings - practical guidance

BRE GBG 3 Damp proofing existing basements

BSI BS EN 752-5 Drain and sewer systems outside buildings rehabilitation

BRE GRG 17 Repairing and replacing ground floors

BRE DAS 73 Suspended timber ground floor : remedying dampness due to inadequate ventilation

BRE Report 466 Understanding Dampness - effects, causes, diagnosis and remedies

BRE Digest 245 Rising damp in walls : diagnosis and treatment

BRE Report 117 Rain penetration through masonry walls : diagnosis and remedial measures

BRE DAS 71 External masonry walls : repointing - specification

BRE DAS 72 External masonry walls : repointing

BRE Report 466 Understanding dampness - effects, causes, diagnosis and remedies

BRE Digest 461 Corrosion of metal components in walls

BRE DAS 107 Cavity parapets : installation of copings, dpc’s, trays and flashings

BRE Reports BRE building elements

BRE GRG 33 Assessing moisture in building materials : sources of moisture

BRE GBG 2 Surveying masonry chimneys for repair or rebuilding

BRE GBG 4 Repairing or rebuilding masonry chimneys

BRE GBG 1 Repairing or replacing lintels

CIRIA Publication C579 Retention of masonry façades - best practice guide

BRE GBG 20 Removing internal loadbearing walls in older property

BRE GRG 22 Parts 1 & 2 - Improving sound insulation

BRECSU GPG 296 Refurbishment site guidance for solid walled houses - roofs

BRECSU GPG 297 Refurbishment site guidance for solid walled houses - roofs

BRE GRG 14 Re-covering pitched roofs

SURVEY(S) OF EXISTING BUILDINGSThe survey(s) should be carried out in accordance with Clause C1. The items listed in this Appendix should be considered andincluded in the survey(s) as appropriate. Causes of defects and damage should beaccurately identified.

(a) previous usageThe survey(s) should establish to what extent the landand buildings included in the conversion or renovationproject have been adversely affected by the formeruse and occupancy.

Any residual contamination caused by the previoususe, e.g. agriculture/industry, should be established bythe survey(s).

(b) contaminantsThe survey(s) should identify contaminants, including radioactive, other toxic, explosive orasphyxiant gases.

Where the ground covered by the building is within 250m of landfill, or where there is reason to suspect that there may be gaseouscontamination of the ground, or where the building will be within the likely sphere of influence of a landfill where gas production is possible, further investigation should be made to establish what protective measures may be necessary.

Further guidance may be found in NHBC Standards Chapter 4.1 ‘Land quality – managingground conditions’.

(c) wood rot and beetle infestationThe survey(s) should be appropriate for the building,taking account of the likelihood of rot and pestinfestation. The survey(s) should not be confined to easily inspected areas, or to areas where rot orinfestation are obvious.

The source, cause and extent of current beetleinfestation or wood rot should be identified.

The BRE publication “Recognising wood rot andinsect damage in buildings” gives guidance.

(d) vermin and pest infestationPoints of entry for vermin and pest should be identified.

(e) foundationsItems to be taken into account include:

• ground conditions/type of soil/varying ground levels

• trees - mature height and root growth

• level of water table, which may have altered since construction

• existing water courses

• level and type of foundations

• structural defects e.g. cracking, signs of movement,deterioration of concrete etc.

• condition of foundations where drains/services passthrough or beneath

• evidence of sulfate attack.

Where appropriate, the effect on foundations ofproposed alterations or extensions to the buildingshould be accounted for in the survey(s).

Satisfactory past performance of foundations may, at NHBC’s discretion, be accepted as demonstratingadequacy provided alterations would not adverselyaffect the foundations.

(f) basementsItems to be taken into account include:

• future use

• structure: ability of the structure to take anyproposed loading condition of the structural floor above

• dampness: damage to the existing structure caused by dampness (i.e. condensation and/ormoisture penetration)

• tanking: feasibility of installing new tanking where required

• ventilation: feasibility of installing ventilation

• drainage and other services.

Satisfactory past performance may, at NHBC’sdiscretion, be accepted as indicating adequacyprovided alterations would not adversely affect the basement.



APPENDIX B



APPENDIX B

(g) below ground foul and surface water drainage Existing drainage should normally be replaced.

Items to be taken into account when assessingexisting drainage include:

• the results of the CCTV survey

• adequacy of existing system (capacity related toproposed use and number of people who will usethe building)

• evidence of leakage

• evidence of surcharging or blockage such as soiled benching

• suitable outfall

• evidence that the flow is self-cleansing

• condition of pipework, manholes and inspection chambers

• location of manholes and inspection chambers

• adequate access for cleaning

• sealing of redundant drainage

• proposals for dealing with existing cesspools andseptic tanks.

(h) ground floorsEffects of proposed alterations on existing floors, andrelated ground levels should be taken into account.

Additional items to be taken into account include:

TIMBER FLOORS

• joist size, span and condition

• bearings to joists

• sleeper walls

• dpcs provided beneath wall plates

• excessive drilling and notching of joists

• condition of related dpm, dpcs (bridged, damaged,not adequately linked)

• effective ventilation of sub-floor void

• sloping or sagging floors, gaps below skirting

• any existing insulation.

CONCRETE FLOORS

• type and condition of floor

• gaps below skirting which may indicate settlementof fill, or subsidence

• bowing, cracking of screed

• cracked or sloping slab which may indicate heave

• evidence of sulfate attack

• effective damp proof membrane – adequatelinking with dpcs

• effective ventilation of sub floor void.

(i) wallsThe type of wall construction should be identified,e.g. masonry with cavity, solid masonry, masonry with rubble fill, timber frame, external leaf fair facebrick, rendering or cladding, regional (eg. stone or cob), concrete, steel or cast iron frame, orproprietary system.

The structural condition should be identified including suitability for alteration.


CRACKINGThe cause of cracking should be identified together with the likely effect on stability; e.g. finecracks (1.5mm max) may not require re-pointing ormasonry repair.

Cracking should be monitored where continuingmovement that could adversely affect the structure is suspected.

More serious cracks can be caused by:

• sulfate attack (expansion of jointing mortar)

• wall tie corrosion (cracking of mortar beds)

• roof spread (walls pushed out of plumb)

• outer leaf pushed outwards, rotation of sills, headsetc. (timber frame ties unsuitable or wrongly fixed)

• subsidence, ground movement (cracks wideningand extending to outer edge of walls).

RENDERING

• many fine cracks (shrinkage or over-strong mix)

• detached from substrate (shrinkage, or effect of sulfate reaction)

• render should not bridge the dpc.

Weathering details should be checked e.g. parapetcopings, sills, eaves, bottom edge of rendering.

SURVEY(S) OF EXISTING BUILDINGS

LATERAL RESTRAINT

• walls that provide end restraint or intermediatebuttressing to external walls should be effectivelybonded or tied to the relevant external wall

• floor and roof timbers should have effectivebearing on supporting walls; lateral restraint straps may be required. Effective anchorage may be required.

STABILITY OF CAVITY WALLSThe survey(s) should establish whether there iscorrosion of wall ties and recommend appropriateremedial action.

CURTAIN WALLING AND CLADDING

• condition of existing system including glazing units,gaskets and seals

• damaged or detached cladding panels

• detached or missing insulation

• damaged or defective fixings

• damaged felt or breather membrane.

(j) support of openingsExisting lintels should be examined to establish theirstructural stability, taking account of possible alteredloadings caused by the conversion or renovation ofthe building.

(k) external walls – rain penetration and dampness


• evidence of rain penetration

• evidence of rising damp e.g. lack of, discontinuous,or defective dpc, or bridged dpc, cavity trays,vertical dpcs

• evidence of internal condensation (staining)

• blocked rainwater goods.

It should not be assumed that solid walls that are dry on the inner face at the time of survey(s), would remain so during adverse weather conditions.

(i) external walls – exposure ratingThe survey(s) should establish the exposure rating of the building. Buildings that were not previouslydwellings will require particular attention, as theexclusion of dampness into the building may not have been critical in the former use.

(m) internal partitionsThe survey(s) should confirm that existing internalpartitions have adequate strength for their purpose.The effect of alterations on existing partitions shouldbe ascertained.

(n) separating walls and floorsThe survey(s) should identify the adequacy of existing separating walls and floors, including theirresistance to:

• spread of fire and smoke (separating walls in some older houses may not continue into the roof space)

• sound.

The above should also be established for walls andfloors which will act as separating elements in theconverted building.

(o) chimneys, flues, fireplaces and hearthsItems to be taken into account include:

• structural stability, including whether rebuilding is necessary

• condition of mortar, pointing, brickwork,rendering, masonry

• condition of flashings and soakers, capping,flaunching or chimney pots

• suitability of flues for proposed appliances

• condition of linings / parging to flues

• proximity of combustible materials to flues/flue pipes

• condition of existing fireplaces, hearths.

(p) timber upper floorsItems to be taken into account include:

• joist size, span and condition

• bearings to joists where bedded in solid brickwork,or joist hangers

• excessive drilling and notching of joists

• sloping or sagging floors, gaps below skirting

• effect of proposed alterations.



APPENDIX B



APPENDIX B

(q) concrete upper floorsItems to be taken into account include:

• type and condition of floor

• where bearing on walls, condition of supportingarea of wall

• condition of supporting beams, and supportingarea of wall

• suitability of floor to take new loadings

• condition of screed.

(r) staircasesItems to be taken into account include:

• structural stability e.g. condition of timbergenerally, excessive movement/sloping of treads,risers, landings; reliability of handrails/balusters

• consistency of rise and going, pitch and headroom

• safety aspects where staircase is lit by glazing

• whether the stairs are safe to use andunobstructed by opening of doors

• suitability for possible use as means of escape incase of fire.

(s) pitched roofs

STRUCTUREItems to be taken into account include:

• size, span and condition of structural members

• evidence of spread

• undulations in ridge line, or in slating/tiling

• adequate triangulation, purlin support

• proper support of water tanks and possibility of extra loading

• joints and connections between members,including metal fasteners (signs of corrosion)

• bracing, lateral restraint

• bearing on supporting structure

• location, dimensions and structural condition ofaccess to loft space

• condition of sarking boards.

WEATHERPROOFING/INSULATIONRoof coverings will normally be removed and replaced.

Where it is proposed to retain any existing pitchedroof coverings, the survey(s) should accuratelyestablish the current condition and anticipateddurability of the coverings e.g. damaged,deteriorated, missing, broken or slipped units.

Additional items to be taken into account include the condition and adequacy of existing:

• flashings

• soffits, fascias and bargeboards etc.

• sarking felt etc

• rainwater disposal goods, gutters and downpipes etc

• insulation

• ventilation.

(t) flat roofs, balconiesRoof coverings will normally be removed and replaced.

Additional items to be taken into account include:

• adequacy of joist bearings, lateral restraint,condition of joists, size and span of joists

• condition of reinforced concrete

• condition/adequacy of insulation within roof system

• condition of guarding, and of its fixings

• adequacy of falls, signs of ponding

• condition of flashings, eaves details

• condition of rainwater disposal.

(u) doors, windows, external joinery and metalwork


• extent of damage or deterioration to aluminium windows

• extent of corrosion to metal windows – whetherrestoration is feasible

• extent of rot in timber windows, doors includingframes, sills, thresholds

• effectiveness of throatings, weather bars and other weatherings

• the condition of existing ironmongery

• security – existing ironmongery may be inappropriate

• safety – additional guarding to openings may be required.

SURVEY(S) OF EXISTING BUILDINGS

(v) glazingExisting insulating glass units should normally be replaced.


• security – existing glazing systems may be inappropriate

• safety – where there is a risk of accidental breakage.

(w) internal joineryItems to be taken into account include:

• condition of joinery

• condition of ironmongery

• condition of internal partitions.

(x) finishesItems to be taken into account include:

• soundness of plaster, plasterboard on walls andceilings etc. where these are to be retained

• condition of decorative work e.g. friezes, cornicesand ceiling roses

• feasibility of providing matching work as required.

(y) services

WATERWhere existing hot and cold water services are to beretained their current condition should be established.


• drinking water

• cold water storage

• hot water storage

• water heating

• distribution – lead pipework should be removedand replaced

• protection against frost

• controls.

ELECTRICALA new electrical service will be required unless it can be shown that the existing service is in a safe condition and will have a reasonable life expectancy.


• the age of the existing installation

• whether the existing installation is suitable for extending.

GASThe gas service should be replaced unless it can be shown that the existing service is in a safe condition and will have a reasonable life expectancy.


• condition/suitability of flues for gas installation

• gas pipes in unventilated voids

• corrosion of steel pipes

• whether the existing installation is suitable for extending.

SPACE HEATINGThe condition and capacity of any existing means of space heating should be established.

ABOVE GROUND DRAINAGE SYSTEMSWhere existing systems are to be retained and/orextended the new system should substantially meetwith current requirements.

(z) Painting and decoratingItems to be taken into account include:

• the condition of existing painting and decoration

• whether existing painting, when cleaned down canprovide a stable substrate for new work to enablesatisfactory and durable finish

• where necessary, timber doors and windowsshould be stripped before redecoration

• metal doors and windows should be strippedbefore redecoration

• any special coatings required e.g. breathable paints.



APPENDIX B



APPENDIX B

(aa) accessItems to be taken into account include:

• condition of existing paths and drives

• levels of paths etc and ground adjacent to the buildings.

(ab) garages and outbuildingsThe survey(s) should identify the condition of buildings which will be used for garages, workshopsor storage, etc and establish their suitability for that use.

(ac) freestanding walls and retaining structuresItems to be taken into account include:

• the stability and condition of freestanding andretaining structures

• the effect of any proposed changes in loading

• the effect of any adjacent excavations or changesin ground levels etc

• that all weatherproofing details necessary to ensuredurability are present and in satisfactory condition.

(ad) garden areas and landscapingItems to be taken into account include:

• the effect of any changes in levels

• any waterlogging within 3.0m of the habitableparts of the building

• whether proposed works increase the risk of such waterlogging

• the effect of any trees or shrubs that have been, or will be, removed.

NHBC, Buildmark House, Chiltern Avenue, Amersham, Bucks HP6 5AP

Tel: 0870 241 4302 Fax: 01494 735201

e-mail: [email protected] www.nhbc.co.uk

NHBC, 42 Colinton Road, Edinburgh, Scotland EH10 5BTTel: 0131 313 1001 Fax: 0131 313 1211

NHBC, Holyrood Court, 59 Malone Road, Belfast BT9 6SA

Tel: 028 9068 3131 Fax: 028 9038 6001

No reproduction without NHBC consent.© NHBC 2005