contents · chapter 6: substructure contents 6.1 basements 6.2 walls below ground 6.3 damp proofing...

CHAPTER 6: Substructure

CONTENTS

6.1 BASEMENTS

6.2 WALLS BELOW GROUND

6.3 DAMP PROOFING

6.4 GROUND FLOORS

FUNCTIONAL REQUIREMENT

Technical Manual TS

-011-09-010412

Workmanship

i. AllworkmanshipmustbewithindefinedtolerancesasdefinedinChapter 1 of this Manual.

ii. Allworktobecarriedoutbyatechnicallycompetentpersoninaworkmanlike manner.

iii.Certificationisrequiredforanyworkcompletedbyanapprovedinstaller.

Materials

i. Allmaterialsshouldbestoredcorrectlyinamannerwhichwillnotcausedamageordeteriorationoftheproduct.

ii. Allmaterials,productsandbuildingsystemsshallbeappropriateandsuitable for their intended purpose.

iii.Thestructureshall,unlessspecificallyagreedotherwisewiththewarrantyprovider,havealifeofnotlessthan60years.Individualcomponentsandassemblies,notintegraltothestructure,mayhavealesserdurabilitybutnotinanycircumstanceslessthan15years.

Design

i. Designandspecificationsshallprovideaclearindicationofthedesignintentanddemonstrateasatisfactorylevelofperformance.

ii. Basementsshallbeappropriatelydesignedtoensurethattheyadequatelyprovideasuitablebarrieragainstcontaminants,groundgases,andgroundwater.

iii.Thebasementdesignshouldbecompletedbyasuitablyqualifiedwaterproofingdesignspecialist.

iv. Basementdesignandconstructionmustbesupportedbystructuralcalculationsprovidedbyasuitablyqualifiedexpert.

v. Designdetailsofthebasementwaterproofingtechniquesmustbeprovidedpriortocommencementonsite.

vi.BasementsmustmeettherelevantBuildingRegulationsandotherstatutoryrequirements,BritishStandardsandEuro-Codes.

.

6.1 SUBSTRUCTURE - BASEMENTS

Technical Manual 2012 - TS

-011-09-010412

CHAPTER 6: SubstructuresCHAPTER

6:SUBSTR

UCTU

RES

incidenceofissueswheresystemsaredesignedwithoutfollowingtheadviceandconsiderationsdetailedwithinBS8102andassociateddesignguides.

SuchscenariosmayoccurwhereProjectDesignerstakeontheroleof‘WaterproofingDesigner’withoutsufficientreferencetothestatedguides,commonlyrelyingonstandarddesigndetailsandwithoutconsideringallappropriatefactors.PleaserefertoBS8102foralistofrequirementsthataDesignermustmeetinordertofulfiltheWaterproofingSpecialistrole.

DesignersmustcarryProfessionalIndemnityinsurancecoverappropriatetotheproject.

Itmustbenotedthatwhererelyingontheuseofwaterproofingproductmanufacturer‘standarddetails’,theytypicallydisclaimdesignresponsibility,soitisincumbentontheWaterproofingDesignSpecialisttoensurethatsuchdetailsarecorrectandappropriateforthesiteandstructure,oroffersuitablevariation.

TheearlyinvolvementofaWaterproofingDesignerisanimportantconsiderationbecausethewaterproofingdesigntypicallyhasaninfluenceonelementsofthestructuraland/orarchitecturaldesign.Earlyinvolvementallowsthewaterproofingtobedulyconsideredinassociationwiththeseotheraspectsandpreventssituationswheredesignfeesareincreasedasaresultofnecessaryredesign,orwaterproofingiscompromisedbyworkingwithintheconstraintsofanill-consideredstructurerelativetoachievingtherequiredstandardofenvironment.

6.1.3 Generalprincipleofwaterproofing design

TheapproachdetailedwithinBS8102involvesassessmentofagivensitetodeterminethecharacteristicswhichinfluencerisk.Withthebenefitofknowledgegainedthroughthisinvestigationandassessment,suitabledesignsfordealingwithgroundwater,gasesandcontaminantscanthenbedevisedandconstructed.

6.1.4 Design responsibility

Productionofasuitabledesignisoneofthemostimportantaspectsinachievingasuccessfuloutcome,wheretherequiredstandardofenvironmentiscreatedwithinthebasementspaceandmaintainedinthelongterm.Acommonassumptioninwaterproofingisthatworkmanshipisthemost‘criticalfactor’andwhilethisisundeniablyimportant,thehigheststandardsofworkmanshipwillnotmakeupforinadequatedesign,andhencecorrectdesignisthefirststepinachievingthedesiredoutcome.

Tothisend,BS8102includesasectionregarding‘designteam’,whichstatesthattheadviceofaGeotechnicalSpecialistbesoughtforassessmentoftheGeologyandHydrogeologyandthat‘aWaterproofingSpecialist’beincludedaspartofthedesignteamfromtheearlieststages,sothatanintegratedandpracticalwaterproofingsolutioniscreated.

TheneedforadedicatedWaterproofingSpecialistwithinthedesignteamisintendedtoreducethe

6.1 Basements

6.1.1 Introduction

ThisChapterprovidesguidanceontherequirementsassociatedwiththedesignandconstructionofbasementsandotherbelowgroundstructures.Principally,thisconcernstheprocessbywhichtheriskofgroundwaterpenetration is appraised and addressed, so that problemsassociatedwithpenetrationdonotoccurwhileconsiderationisalsogiventoeconomicconstruction.

ThisprocessandrationaleisprimarilydetailedwithintheBritishStandard8102(2009)CodeofPracticeforprotectionofbelowgroundstructuresagainstwaterfromtheground(andotherassociateddesignguides).However,furtherpracticalguidanceonthisandcompliancewithwarrantyrequirementsisincludedherein.

6.1.2 Limitations of guidance

ThisdocumentisnotintendedasastandalonedesignguideanddoesnotincludethefulldetailofwhatmustbeconsideredtocomplywithBS8102.See‘references’fordetailsofotherassociateddesignguides.

Itmustalsobenotedthatstructuralwaterproofingdesignandgeotechnicalinvestigationarespecialistfieldsandwhilegeneralguidanceisprovided,advicemustbesoughtfromsuitablyexperiencedparties.AppropriatestructuraldesignmustbeundertakenbyaCharteredStructuralEngineer.


-011-09-010412


6:SUBSTR

UCTU

RES

reasonabledoubtastogroundwaterconditions,pressuretothefullheightofthebelowgroundstructuremustbeassumedatsomepointinthelifeofthestructure.

TheSiteAuditSurveyormayrequestacopyoftheSiteInvestigationReport,DesignersRiskAssessmentandassociateddesignrationale.

6.1.6 Water resisting design

Theprincipleofthisistoconsideranddesignforthepressureswhichthestructure/waterproofingmustresistbaseduponthesiteinvestigationandriskassessmentdetailedabove.However,italsoconcernsthemeansbywhichthedegreeofwaterinthegroundcanbeinfluencedbydesign:

6.1.6.1 Structural resistance

Theabilityofthestructuretoprovideresistancetothepenetrationofwaterhasabearinguponallformsofwaterproofing.

Retainingwallsinplainorreinforcedmasonryprovidecomparativelylittleresistancetothepenetrationofwaterunderpressure,becauseofthecrackpatternassociatedwiththedegreeofjoints(mortarbeds)present.

Thedegreeofwaterexcludedbyconcreteelements(wallsandslab)isinfluencedbythenatureofthedesignandconstruction.Whileconcreteinitselfisrelativelyimpermeable,thedegreetowhichwaterisexcludedwillgreatlybeinfluencedbycracksizesanddetailingofconstructionjointsandservicepenetrations.

tocometobearandshouldalsoreceiveconsideration.

FurtherguidanceonthedrainagecharacteristicsassociatedwithdifferenttypesofgroundisincludedwithintheBasementInformationCentrepublication;Basements:Waterproofing–GeneralGuidancetoBS8102:2009.

Groundgasesandcontaminantsmustalsobeconsideredwithintheriskassessment.

Itmustbenotedthatwhilethesiteinvestigationformspartofwhatguidesthewaterproofingdesign,anequallyimportantconsiderationistheintendeduseofthespaceandimplicitconsequencesintheeventthatwaterpenetrationoccurs.Forexample,inpropertieswheretheconsequencesofpenetrationwouldbesevere,suchasinhabitablespace,suitablylowriskmethodsmustbeprovided. Furthermore,whilstonecouldintheoryassumethatbaseduponasiteinvestigation,theriskofwaterpressureevercomingtobearislow,BS8102advisesthatconsiderationisgiventotheeffectsofclimatechangeandburstwatermainsandsewers,aswellasstatingthatoneshouldassumethatthereisriskofwaterlogging‘evenwheresiteexaminationindicateddryconditions’.

Insummary,thesiteinvestigationguidesthedesignbutoneshouldneverassumethatsomedegreeofwaterpressurewillnotcometobear.

Furthermore,andparticularlyifnositeinvestigationhasbeenundertakenorthereis

Designersmusthaveon-goinginvolvementduringthebuild,maintaininggoodcommunicationwithsitemanagementandprovidingsupervisionandguidancewherevernecessary.

6.1.5 Site and risk assessment

Thedegreeofwaterpresentwithintheground,andthepropensityforwaterloggingtooccuroverthelifetimeofastructureisaprincipledriverinassessingriskandthedegreeofwaterproofingrequired.Simplistically,ifabasementisconstructedintoapermanenthighwatertable,thenthedegreeofprotectionwillnecessarilybegreaterthanasimilarstructureconstructedintoagenerallydrysite.

Assessment of a site must be based on the results ofthesiteinvestigationandothersitespecificfactors.

Seasonalvariationsinthewatertablemustbeaccountedforunlesslongtermmonitoringisundertaken.However,evenwherestandingwaterlevelsarenotnotedduringsuchpre-startsiteinvestigation,thedrainagecharacteristicsofthegroundmustreceiveparticularattention.Soilswithlowpermeabilityrepresentriskofwaterlogging,orencouraging‘perchedwatertable’,wherewaterstandstemporarilyorpermanentlywithinthegroundagainstastructure,andarguablythisaffectsmorepropertieswithbasementsversusthetruewatertablelevel.

Otherfactorssuchastopographyandorientationmayhaveabearingonthepropensityforpressure


-011-09-010412


6:SUBSTR

UCTU

RES

Landdrainpositioningisacriticalconsideration,specificallyinrespectofsystemswherethereisnoviableaccessforrepair(orsuitablerepairstrategy).Furthertotheadvicedetailedwithinthe‘defectsandremedialmeasuressection’,itisnecessaryinthiscircumstancetoincludelanddrainsatalowenoughpositiontopreventpressurefrombearinguponthestructureandwaterproofing,sothatthepresenceofanypossibledefectsaremitigated.

Theviabilityofincludinglanddrainageanditspositioningshouldbeconsideredinassociationwithallmethodsofwaterproofingasameanstoreduceriskgenerallyatnominalcostimplication.

Theuseofgeo-drainagemembranesappliedtotheexternalfaceofaretainingwallcanprovideacontinuousdrainagespaceexternalofthestructurewhichassistsinencouragingwatertodraindowntothelevelofthelanddrainswithoutpressuringonthestructure.

granularandclaysoilswherelanddrainsaresusceptibletoclogging.

• Roddingpointsmustbeincluded(ideallyatchangesindirection)tofacilitatemaintenance,whichwillallowthesystemtofunctioninthelongterm.Thismaintenanceshouldbeundertakenatsuitableintervals(annuallyasaminimum),withthedetailofthisbeingwrittenintothedocumentationpassedtohomeowners.

• Landdrainsmustlinktoareliablepointofdischarge.Wheresumppumpsystemsareemployed,theimplicationsofpowercutsshouldbeconsideredinthatlanddrainsmayinsuchscenariosnotfunctionasintended.Theeffectivenessofbatteryback-upsystems,whereemployedinsumpsservicinglanddrainsshouldbeconsideredinrelationtoassessmentofthelikelydegreeofgroundwater.

Itisnotunknownforissuesofwaterproofingfailuretooccurwherelanddrains,(thatformpartofthewaterproofingsystem),arelinkedintosoakaways.Thelimitationonsoakawaysisthatdependingonthenatureoftheground,theymaybecomesaturated(similartothegroundaroundabasement),meaningthatnomorewatercanbeaccepted,withpressuresubsequentlycomingtobearuponthestructure.Insuchcases,thesoak-awayoftenalsoacceptswaterfromrainwatergoods;thisprovidingadirectpathforwaterfrom the roof to the basement. Therefore, land drainsmustnotbedirectlylinkedtosoakawaysbygravity,unlessitisnotpossibleforwatertosurcharge,i.e.,wherethetopofthesoak-awayisbelowtheleveloftheactuallanddrains.

6.1.6.2 Exclusion of surface water

Surfacesexternalofthebasementstructureatgroundlevelcanacttolimitorattenuatepenetrationintovulnerablepositions,i.e.,themorepermeableexcavatedandbackfilledgrounddirectlyaroundthebasementstructure.Theinclusionofsurfaceandcut-offdrainswhichremovestandingwaterawayfromthevulnerableareasalsobenefit.

6.1.6.3 Sub-surface drainage

Theuseoflanddrainagecanacttoremovewaterfromaroundthestructure,thusalleviatingpressureandreducingriskaccordingly.

Theuseoflanddrainageisnotviableonallsites,examplesbeingwherethereisnoavailablelocationtodischargecollectedgroundwater,orwherehighwatertablesandpermeablegroundconditionsmakeitimpracticaltosufficientlyremovethequantitiesofwaterpresent.AGeotechnicalSpecialistand/orWaterproofingSpecialistcanadvisefurtherinthisrespect.

Notwithstandingsuchconditions,theprovisionofeffectivelanddrainsisoftenaneconomicmeansofgreatlyreducingriskandmustbeincludedwhereviable.

Thefollowingconsiderationsapply:

• Perforatedlanddrainsmustbesurroundedincleangradedstoneandwrappedinasuitablegeo-textilefilterfabrictoreduceriskofclogging.Thisisparticularlyimportantinfine


-011-09-010412


6:SUBSTR

UCTU

RES

Wherelanddrainsareincludedthisshouldbeinassociationwithapermeablestonebackfillcompactedinlayers,whichalsoencourageswatertodraindowntothelevelofthelanddrainswithoutperchingandpressuringuponthestructure.

Furthermore, the use of maintainable land drains isanecessitywhereemployedinassociationwithsomeformsofinaccessible/externaltankingsystems,i.e.,wherethestructureitselfprovideslittleresistance.Insuchcases,ifitisnotfeasibletoincludereliablelanddrains,alternativemethodsofwaterproofingmustbeused.

TheSiteAuditSurveyoristobesuppliedwithdesigndetailswhereexternallanddrainageisincluded.

6.1.7 Intended use and required standard of environment

Usagedictatestherequired‘grade’ofenvironment,orinotherwordshow‘dry’agivenbasementspacemustbeinordertobesuitableforagivenusage.TheDesignermustthereforeconsiderhowthiswillbeachievedinaparticularsiteandstructure.BS8102providesthreedefinitionsofenvironmentalgrades(Grades1,2and3).

Notably,habitablespaceisGrade3,wherewaterpenetrationisunacceptable.Appropriatelydesignedenvironmentalcontrols,suchasvapourbarriers,insulation,heating,ventilationanddehumidificationmustbeincludedtocontrolvapourintroducedviaoccupationsufficiently,therebypreventingproblemsofcondensation.

Figure 1: Suitable position of land drains


-011-09-010412


6:SUBSTR

UCTU

RES

penetrate,wherepressurecomestobear;• Loading,wherehydrostaticpressureisapplied

tothestructureasaresultofexclusionviathetankingmedium,i.e.,structuresmustbedesignedtoresistloadsappliedtothem;

• Continuity,inthatsystemsmustinvirtuallyallcasesbe‘continuous’,inthatagapinabarriersystemrepresentsapointatwhichwaterunderpressurecanpenetrate;

• ‘Buildability’,namelywherebysheetmembraneproductsareproposed,withtheconsiderationbeingthepracticalityofwrappingaflatsheetaroundcomplexthreedimensionalshapessuchasexternalcornersandbeneathraftslabthickenedtoedetails.

Strategiesforrepairofagivensystemmustbeconsideredaspartofthedesignprocess.Furthercommentaryisprovidedwithineachofthespecificsystemtypesections.

ThedetailofanappropriaterepairstrategymayberequestedbytheSiteAuditSurveyorinrelationtoagivenwaterproofingdesign.

6.1.9 Formsofwaterproofing

BS8102definesthreeformsofwaterproofingprotection;TypeA:BarrierProtection(commonlyreferredtoas‘tanking’),TypeB:StructurallyIntegralProtection,andTypeC:DrainedProtection.

6.1.9.1 Type A: Barrier Protection

Thisformofwaterproofingreliesontheinclusionofaphysicalbarriermaterialappliedonorwithinthestructure;oftenwherethestructureitselfprovideslittleresistancetothepenetrationofwater.

Avarietyofconsiderationsapply:

• Suitabilityofthesubstrate,primarilyapplicablewheretankingproductsareappliedinternally,inthatthebondbetweentheproductandthesubstrateonwhichitisappliedmustbesufficienttoresisthydrostaticgroundwaterpressure;

• Therequirementforpreparationofsubstratestoaccepttankingmediums;

• Movement,whichinrigidtankingsystemsmayencouragecrackingthroughwhichwatermay

ExampleusageforGrade2includesstorerooms,andagainwaterpenetrationisnotacceptable,however,heatingandventilationisnotnecessarilyrequired,albeitthatsomedegreeofventilationisrecommendedeveninbasicstoragespacewhichmayotherwisesuffercondensationrelateddampness.

Grade1differsinthatsomedegreeofliquidwaterpenetrationisacceptable,i.e.,minimalseepageaslongasaspaceremainsfitforpurpose.ExamplesofGrade1includebasiccarparking.

MostbasementsshouldbeconstructedtoallowaminimumofGrade2,with3beingnecessaryforoccupiedspace.Grade1issuitableforbasementcarparkingonly(excludingbasementstoreroomsandaccesswells)andthisshouldbeagreedonaperschemebasis.

6.1.8 Defects and remedial measures

WithinBS8102,Designersareadvisedtoconsidertheprobabilitythatsystemsmaynotbeinstalledperfectlyandthatdefectsmayoccurasaresultofthis,orthatdefectsmaybepresentinsupplied materials.

Designingontheassumptionthatasystemwillnotbetotallyperfectorfreeofdefectsnecessitatesthatconsiderationisgiventothefeasibilityofrepairingthosedefects,orensuringthattheyareofnoconsequence,suchaswheresystemsarenotaccessibleforrepair.Differentstructures,waterproofingsystemsandsiteshaveabearinguponthisconsideration.


-011-09-010412


6:SUBSTR

UCTU

RES

Figure 2: Type A barrier protection

Withregardtorepairstrategies,internalsystemshavethebenefitofgreateraccessibility,meaningthatrepairismorefeasible.However,beingappliedtotheinternalfaceofthestructure,theimplicationsofpreparation,strengthofsubstrateandbondbecomesmuchmoreimportant.

Externalsystemshavegreaterimplicationinthataccessibilityforrepairistypicallyimpracticalpostconstruction,andwherecombinedwithrelativelypermeablewallconstructions,makeitdifficulttoconfidentlydeterminethepointofadefectexternally,becausewatercantrackwithinthewallconstructiontoshowitselfinternallyatapositionnotlocaltothedefectexternally.

OnthebasisthatBS8102advisesthat‘repairability’mustbeconsidered,theuseofexternaladhesivemembranetankingsystemsonpermeableconstructionsisprecluded,unlessemployedinassociationwithlongtermstrategiesforpreventinggroundwaterfrompressuring,e.g.,serviceablelanddrains.

Theuseoflanddrainstopreventpressurecomingtobear,addressestheconsiderationthatdefectsmayoccurbecauseifpressureisnotallowedtocometobear,thenthesedefectswillnotallowpenetrationandsoareofnoconsequence.

Riskcanbelessenedbyusinga‘fullybonded’tankingsystem,wherethebondissuchthatwatercannottrackalongbetweenthestructureandtankingproduct,inassociationwithastructureoflesserpermeabilitywhichwouldallowlocalisedrepair to be undertaken.


-011-09-010412


6:SUBSTR

UCTU

RES

6.1.9.2 Type B structurally integral protection

TypeBalsoreliesontheexclusionofwater,butemploysthestructureitselfasopposedtobarrierproductsincludedonorwithinit.Inthemain,TypeBisformedusingreinforcedconcrete;howeverthismaytakeseveralforms.

Figure 3: Type B Structurally integral protection

Concretewithoutadditiveandincludingmoretypicallevelsofsteelreinforcement(withcracking<0.3mm),whileprovidingagoodresistancetothepenetrationofwater,willallowseepage,givenhydrostaticpressureandassuchisnotsuitableinisolationunlessformingbasic(non-habitable,non-storage)standardsofenvironment.

Aswithanystructurewhichaimstoentirelyblockoutwater,thismustbefreeofdefectswhichwouldotherwise allow water to penetrate.

Inachievingthis,thefollowingmustbeconsidered:

• Structuraldesignandspecificationofmaterials(basedinpartonsiteassessment);

• Waterstopdetailingatconstructionjoints;• Servicepenetrationdetailing;• Appropriatespecialistsitesupervisionto

ensurehighstandardsofworkmanship;• Goodplacementandcompaction;• Curing.

ParticularconsiderationmustbegiventotheformationofconstructionjointdetailswhichformatypicalweakpointinTypeBstructures.Furthermore,specialistsupervisionisrequiredonsiteduringconstruction.

Systemswhichfunctionbyexcludingwatermaynotbetesteduntilgroundwaterpressurecomestobear.Therefore,itisadvantageouswhereexternalwaterpressurecomestobearpriortocompletionthatanyareasofpenetrationcanberemediedduringconstruction.

Wheretheobjectiveisforthetotalexclusionofwater,additionalsteelreinforcementcanbeincludedtolimitcrackingtolessthan0.2mmthroughwhichwaterwillnotpass.Alternatively,additivescanbeincludedtoreducepermeability,withwaterbeingexcludedwithouttheadditionofsteeloverandabovethatwhichwouldnormallyberequiredaspartofthestructuraldesign


-011-09-010412


6:SUBSTR

UCTU

RES

Withregardtoappraisalofrepair,thismethodhasabenefitinthatthepointofpenetrationistypicallythepointofthedefectorpathwaythroughwhichwaterpenetrationoccurs.Coupledwiththeimpermeablenatureofthestructuregenerally,thisallowslocalisedrepairtobeundertakenviaresininjection,groutingandassociatedrepairmethods.Themainconsiderationislocatingthepointofanypenetrationanditisthereforebeneficialwherereasonableaccesstotheconcretestructureremainsviable. 6.1.9.3 Type C drained protection

ThismethodofwaterproofingdiffersfromTypeAandBinthatasopposedtoexcludingwaterentirelythestructureisemployedtolimitpenetration,whileaninternaldrainagesystemcollectsandremoveswater.Thisisolatestheinternalenvironmentfromanywatercontainedwithinthesystem.

Suchsystemscomprisethreeelements:

• Adrainagechanneldetailtypicallyconcealedwithinthefloorconstruction.

• Ameansofwaterdischargewhichinabasementfullybelowgroundrequiresasumppumpsystemorinaslopingsitemaybeviagravity.

• Vapourbarrierdrainagemembranesincludedaboveorinternalofthedrainagesystemwhichisolatetheinternalenvironmentfromthedampsubstrates behind.

Figure 4: Type C drained protection


-011-09-010412


6:SUBSTR

UCTU

RES

Whereelementsofthedrainedprotectionsystemareincludedwithincavities,cavitiesmustbekeptclearofmortarsnotsanddebris.

Continuityofthestructuremustbeconsideredbecauseresistancetowaterprovidedbyagivenstructureisreducedbyaperturesthroughwhichwatercanfreelymove.Examplescouldincludeholespresentwithinexistingbuildings,orinnewconstructionwherelanddrainsarelinkedtosumppumpsystems,withthesumpsbeinginstalledinternaloftheretainingshell,e.g.,inlightwells,thusprovidingapathwayforwatertoenter.

Temporary110vpumpsshouldbeincludedduringconstructiontoaddresswaterpenetrationasnecessary.240vsystemsshouldbeinstalledandcommissionedassoonasisviableonce240vsupplies are installed.

Systemsmustnotlinkdirectlybygravitytosoakaways,whereanyofthereasonspreviouslystatedoccurbecauseofthedangerofbackflowofwaterthroughthepipesorwaterloggingofthelocalgroundaboveslab/DPMlevel.However,wheresuchconditionsarenotpresent,sumppumpsystemsmaybeemployedtoliftwateruptogroundlevelexternally,dischargingintogullieslinkedtosoakaways.ThisdetailshouldbedesignedbytheWaterproofingSpecialist.

Inconsiderationofrepairofdefects,theinclusionofdrainedprotectionsystemsinternallygenerallyensuresthatsystemscanbeaccessedforlocalisedrepair,howeverthismaybelessenedwheresystemsaresandwichedwithinthestructure,i.e.,withincavities.

over-flowdetailmustbeemployedtoallowwatertospillexternallyintheeventofissue.

Internaldrainedprotectionsystemsmustincludedrainagechannelslocaltotheexternalwallfloorjunctions,whichfacilitatesmaintenanceandallowssystemstofunctionandprotectinthelongterm.Wherelargerfootprintsareinvolved,crossfloorchannelsmustbeincluded,ideallylocaltoconstructionjointswherethestructureismorevulnerabletogroundwaterpenetration.

Systemsmustbemaintainedannuallyasaminimum.Thedetailofthisrequirementmustbeincludedwiththedocumentationprovidedtothehomeowner.

Watermovingoverandthroughnewconcreteleachesfreelimewithintheearlylifeofthestructureandsuitabletreatmentsshouldbeappliedtoconcretetominimisethis.

Substratesshouldbecleanandfreeoflooseorfriablematerialspriortotheapplicationofmembranelinings.

Floodtestingofasystemshouldbeundertakenduringconstructiontocheckefficacyandthatwaterflowsfreelytothedischargepoint.Testinginthismannertoprovethatasystemfunctionsasintendedisakeybenefitofthismethodofwaterproofingandmustbepartoftheprocess.

Systemscreatinghabitablespacerequiretheinclusionofvapourbarrierdrainagemembraneswithinthewallandfloorconstruction.

Drainedprotectionsystemsarereliantontheirabilitytoremovewaterandsothemechanismbywhichwaterisremovedrequirescarefulconsideration.Theextentofpenetrationalsohasabearingonthecapacityrequired,withthedegreeofpenetrationbeinginfluencedbythepermeabilityofthestructureandthegroundwaterconditionsexternally.

Notwithstandingtheabove,thecapacityofsuchsystemstoremovewatermustbeadequatetodealwithaworstcasescenario,andshouldbeengineeredwiththisinmindtoprovideasuitablylowrisksystem.

Sumppumpsystemsmustincludemechanicalredundancy(dualmainspoweredpumps)toprotectagainstpumpfailure,andalsosufficientbatteryback-upprotectiontoprotectintheeventofapowercut.

EachpumpwithinagivensystemshouldhaveindependentdirectspurRCD/powersupply,sothatintheeventofanissuewithapump,theotherswillstillhavepower.Directspurisadvisedtopreventaccidentalturningoffbyhomeowners.

Drainagesystemstypicallydischargeintosurfacewatergulliesatexternalgroundfloorlevel,andanover-flowdetailmustbeformedatthepointofdischarge,toallowwatertospilloutexternallyintheeventofdrainsblockingorsurcharging.

Systemscandrainbygravitytolowgroundexternally,i.e.wherepropertiesarepartretainingandconstructedintoslopingsites.Aswithpumpedsystems,ifconnectingtomainsdrains,an


-011-09-010412


6:SUBSTR

UCTU

RES

Partoftheunderlyingrationaleofdrainedprotectionisthatwaterisremovedcontinuously,sothatitdoesnotcollectandremovespressureuponmembraneliningsinstalledoverthedrainage.Ifwaterdoesnotpressureuponsuchmembranes,thentheincidenceofanydefectswithinthemisgenerallyofnoconsequence,andsomaintainingtheefficacyofthedrainageinthelongtermensuresthatsuchdefectsarenegated.

Figure 5: Combined protection

6.1.11 Ground gases and contaminants

Aggressivegroundconditionsmayrequiretheinclusionofasuitablegroundbarriertoprotectthestructureappropriately.Specialistadvicemustbesoughtinrespectofdealingwithgroundgases,andDesignersareadvisedtocheckcurrentstandardsatthetimeofconstructionforsuitableguidance.

6.1.12 Existing structures

WaterproofingexistingstructuresdiffersfromnewconstructioninthatDesignersmustworkwithintheconfinesoftheexistingstructure.However,manyofthesameconsiderationsapplyinthattherequiredstandardofenvironmentappropriatetousagemustbecreatedandmaintainedinthelongterm.

6.1.10 Combined protection

Combinedprotectionviatheinstallationoftwoformsofwaterproofingcanbeemployedtosubstantiallylowertheriskandmaybenecessarywheretheconsequencesoffailureareparticularlygreatand/orwheredifficultsiteconditionsresultinunacceptablyhighriskwhenemployingasinglesystem.


Technical Manual TS

-011-09-010412

Workmanship



Materials




Design


ii. StructuralelementsoutsidetheparametersofApprovedDocumentA(EnglandandWales)Section1(Scotland)andTechnicalBookletD(NorthernIreland)mustbesupportedbystructuralcalculationsprovidedbyasuitablyqualifiedexpert.

iii.ThedesignandconstructionmustmeettherelevantBuildingRegulationsandotherstatutoryrequirements,BritishStandardsandEuro-Codes.

.

6.2 SUBSTRUCTURE-WALLS BELOW GROUND


-011-09-010412


6:SUBSTR

UCTU

RES

6.2.1 Bricks and blocks below ground

BricksshouldbeselectedthatareappropriatelydurableagainstsaturationinaccordancewithBS3921;brickandblockclassificationsthataresuitableforwallsuptoDPCcanbefoundinTable1.

Iftherearesulphatesinthegroundand/orthereisgroundwaterpresent,confirmationbythemanufacturerthatthebrickorblockissuitableforusebelowgroundshouldbeprovided.

Brick / Block type Use / Minimum standard of brick or block

WallsuptoDPC WallsuptoDPC(sulphatesinsoils)

Claybricks FL,FN,ML,MN (a) FL,FN,ML,MN (a)

Calciumsilicatebricks Class 3 (b) Class 3 (b)

Concretebricks Minstrength20N/mm2 Minstrength20N/mm2 (c)

Blockwork Minstrength7N/mm2anddensitygreaterthan1500kg/m3(d)

Minstrength7N/mm2anddensitygreaterthan1500kg/m3 (d)

Notes:(a):IfthesiteiswetorsaturatedatgroundleveluseFLorFNbricksonly (b):Denotesaminimumstandard-higherclassificationsmaybeused. (c):ForClass1andClass2sulphates,checkwithmanufacturerstoconfirmsuitabilityofbrick;forClass3sulphates,use engineeringqualityconcretebricks. (d):Autoclavedaeratedblockswithindependentappropriatethirdpartycertificationareacceptable.

Table 1: Suitability of bricks and blocks below ground


-011-09-010412


6:SUBSTR

UCTU

RES

6.2.2 Mortar mixes

MortarsbelowdampproofcourseareexposedtohighersaturationandthereforerequireahigherdurabilityasindicatedinTable2.

Proportion by volume

Classification Portlandcement:lime:sand

Air-entrainedportlandcement:Sand

Masonrycement:sand

Strength

Highdurabilitymortarforausebelowornearexternalgroundlevel

(ii)(a) 1:0.5:4-4.5(b) 1:3-4(b) 1:2.5-3.5(b) 5.0N/mm2

Notes: (a):Forconcreteorcalciumsilicatebrickuseadesignation(iii)mortar (b):Wheresoilorgroundwatersulphatelevelsareappreciable(Class3orhigher) usesulphateresistingPortlandcement.

Table 2: Typical mortar mixes for below ground masonry

6.2.3 Cavities below ground

CavitiesbelowgroundshouldbefilledwithconcreteensuringthereisaminimumgapasindicatedinFigures1and2betweentheDPCandthetopoftheconcrete.TheconcreteshouldbeofaGEN1gradeandaconsistenceclassofS3.

Figure6:Concretecavityfill-traditionalgroundbearing slab

Figure7:Concretecavityfill-beamandblockfloor


Technical Manual TS

-011-09-010412

Workmanship


ii.Allworktobecarriedoutbyatechnicallycompetentpersoninaworkmanlike manner.

iii.Certificationisrequiredforanyworkcompletedbyanapprovedinstaller.

Materials




Design


ii. Damp-proofingworksshouldpreventanyexternalmoisturepassingintotheinternalenvironmentofthedwelling.

iii.StructuralelementsoutsidetheparametersofApprovedDocumentA(EnglandandWales);Section1(Scotland)andTechnicalBookletD(NorthernIreland)mustbesupportedbystructuralcalculationsprovidedbyasuitablyqualifiedexpert.

iv. ThedesignandconstructionmustmeettherelevantBuildingRegulationsandotherstatutoryrequirements,BritishStandardsandEuro-Codes.

.

6.3 SUBSTRUCTURE - DAMP PROOFING


-011-09-010412


6:SUBSTR

UCTU

RES

6.3.3 Stepped membranes

DampproofmembranesshouldbecontinuouswherefloorsaresteppedasillustratedinFigure8.

Figure 8: Stepped damp proof membrane

6.3.1 Damp proof courses

Dampproofcoursesshouldbeofaflexiblematerialwhichissuitableforitsintendeduse.Thedampproofcourseshouldhaveappropriatethirdpartycertification.Generally,bluebrickorslateswillnotbeacceptedasadampproofcourse.

Dampproofcoursesshouldbelaidonamortarbedandcorrectlylappedatjunctionsandcorners.The depth of lap should be the same as the width of the DPC.

Dampproofcoursesshouldnotbridgeanycavitiesunlessitisactingasacavitytray

6.3.2 Damp proof membranes

Dampproofmembranesshouldbeprovidedbeneathallgroundsupportedslabsorcastin-situreinforcedslabs.Membranesshouldbelinkedtothedampproofcourseandshouldbeaminimum1200gpolythene.Membranesshouldbeeitherlaidontoaconcreteslaborontoaminimum25mmsandblinding(iflaidbelowafloorslab).

Otherdampproofmembranesmaybeconsiderediftheyhaveappropriatethirdpartycertificationandareinstalledinaccordancewithmanufacturer’sinstructions.


Technical Manual TS

-011-09-010412

Workmanship



Materials




Design


ii. StructuralelementsoutsidetheparametersofApprovedDocumentA(EnglandandWales);Section1(Scotland)andTechnicalBookletD(NorthernIreland)mustbesupportedbystructuralcalculationsprovidedbyasuitablyqualifiedexpert.

iii. ThedesignandconstructionmustmeettherelevantBuildingRegulationsandotherstatutoryrequirements,BritishStandardsandEuro-Codes.

iv. Pre-caststructuralelementsmusthavestructuralcalculationswhichprovetheiradequacythathavebeenendorsedbythemanufacturer.

.

6.4 SUBSTRUCTURE- GROUND FLOORS


-011-09-010412


6:SUBSTR

UCTU

RES

additionalmembraneisincorporated,whichisshowninFigure9.

6.4.1.4 Concretingoffloors

Priortoconcreting,anywaterordebriswhichmayhavecollectedontopoftheDPMshouldberemoved.ConcreteshouldideallybereadymixedandbeofatleastGEN3.Expansionjointsshouldbeprovidedinaccordancewithsection2.2ofthisManual.

6.4.2 Suspended reinforced in-situ slabs

6.4.2.1 Structural design

Acastin-sitususpendedconcreteslabshouldbedesignedbyaqualifiedStructuralEngineer.Thestructuraldesignshouldincludethefollowinginformation:

• Adequacyofwallswhichsupporttheconcreteslab(intermediateandperimeterwalls);

• Suitablethickness,correctdurabilityofconcreteandcorrectprovisionofreinforcing;

• Provisionofanti-crackreinforcingtotheperimeteroffloors.

6.4.2.2 Site preparation

Thematerialbelowtheproposedfloorslabshouldbecompactedsufficientlytosupporttheslabduringpouringandcuringstages.Anybackfillmaterialshouldnotcontainanyorganicmatter,containcontaminantswhichcouldreactwiththeconcreteorbesusceptibletoswellingsuchascollierywaste.

6.4.1.2 Damp proof membranes

Dampproofmembranescanbelaideitheraboveorbelowthefloorslabdependingonthefinishofthefloor.ThemembraneshouldbelappedintotheDPCbyatleast100mm.

Figure9:Typicalgroundbearingfloorslab

6.4.1.3 Insulation

Insulationthatistobeprovidedtogroundfloorcanbeplacedeitheraboveorbelowtheconcreteslab.Insulationshouldbeinstalledinaccordancewithmanufacturer’sinstructionsandbedurableenoughtowithstandfloorloadingsandmoisture.Anumberofinsulationproductsrequireanadditionaldampproofmembranetoprotectthesurfaceoftheinsulation.Itisimportantthatthis

6.4.1 Groundsupportedconcretefloors


Thesitebeneaththefloorshouldbestrippedofalltopsoil,organicmatterortreerootspriortofillingandcompaction.

Suitablehardcorewouldincludeinertquarriedmaterialsuchaslimestoneorgranite.Recycledaggregatesmaybeusedwhichincludecrushedconcreteorbrokenbrick,however,thesemustbecompletelyfreeofcontaminantsandplasterandshouldbedeliveredtositefromasupplierthathasaqualityauditprocessinplace.

Materialswhichareavailableasaresultofanysitedemolitionshouldnotbeusedashardcorebeneathfloorslabsunlessspecificallyagreedbythesiteauditsurveyorandonlythenifitcanbedemonstrated,thatthematerialiscompletelyfreeofcontaminantsandplaster.

Hardcoreshouldbeplacedandcompactedin150mmnominallayersandbefullyconsolidatedusingamechanicalcompactor.Agroundsupportedconcretefloorwillnotbeacceptablewherethedepthofhardcorerequiredexceeds600mm,andanalternativegroundfloorsolution,e.g.,beamandblockshouldbeconsidered.

Hardcorematerialshouldnotbesaturatedandcautionshouldbetakentoensurethatnewwallsarenotdisturbedbycompactionofthehardcore.


-011-09-010412


6:SUBSTR

UCTU

RES

6.4.2.5 Concretingfloors

Thedepthofconcretewillvarydependingupontheloadconditionsandthespanofthefloor.TheoverallreinforcedconcreteslabdesignshouldbedesignedbyasuitablyqualifiedStructuralEngineer.

ThereinforcedconcreteshouldhaveaminimumstrengthofRC30andbereadymixedanddeliveredonsiteinaccordancewiththefunctionalrequirementsofsection2.2Materials-concretesitemixingisnotconsideredsuitableforconcretesuspendedfloors.

Thepouredconcreteshouldbelightlyvibratedandwelltampedtoensurethatnovoidsareleftwithinthefloorslab.

Thefloorslabshouldbeappropriatelyshutteredarounditsperimetertoenableacavitytobeformedbetweentheexternalwallandfloorslab.Theshutteringcanbeexpandedpolystyrene,(whichisremovedoncetheconcretehasset)oraproprietaryshutteringsystem.

6.4.2.6 Reinforcing

6.4.2.6.1 Reinforcing cover

Themainreinforcingbarsmusthaveaminimumconcretecoverof40mm.Suitablespacersshouldbeprovidedtosupportthereinforcingpriortoconcreting.

6.4.2.3 Damp proof membranes

Dampproofmembranescanbelaideitheraboveorbelowthefloorslabdependingonthefinishofthefloor.Ifthemembraneistobeplacedbeneaththeconcrete,extracautionshouldbetakentoensure the membrane is be lapped into the DPC byatleast100mmasshowninFigure9.

Figure 10: Typical cast in-situ concrete suspended floor

6.4.2.4 Insulation

Insulationthatistobeprovidedtogroundfloorshouldbeplacedabovetheconcreteslab.Insulationshouldbeinstalledinaccordancewithmanufacturer’sinstructionsandbedurableenoughtowithstandfloorloadingsandmoisture.Anumberofinsulationproductsrequireanadditionaldampproofmembranetoprotectthesurfaceoftheinsulation.

Figure11:Castin-sitususpendedconcretefloor- reinforcing cover and support

Thereinforcingfabricmustbelaidsothemainbarsareinthesamedirectionasthespan


-011-09-010412


6:SUBSTR

UCTU

RES

6.4.2.6.3 Lapping of reinforcing

Itisacceptedthatreinforcingcanconsistofanumberofsheetswhichcanbejoinedtogether.ThedepthofcoverwillvaryonthethicknessofmeshreinforcingandisidentifiedinTable4.

Minimum laps for main reinforcing bars in fabric mesh (1)

Fabrictype Minimumlap(mm)

B1131 500

B785 400

B503 350

B385 300

B283 250

B196 200

Note: 1)Aminimumlapof300mmisrequiredfor secondaryreinforcingbars.

Table 4: Minimum laps for reinforcing

Figure 12: Typical reinforcing lap

6.4.2.6.2 Standard of fabric reinforcing

Reinforcingfabricshouldbefreefromlooserust,oil,grease,mudandanyothercontaminantswhichmayaffectthedurabilityoftheconcrete.

BS Reference Primary bar Secondary bar

Size(mm) Spacingofbars(mm)

Area mm2/m Size(mm) Spacingofbars(mm)

Area mm2/m

B1131 12 100 1131 8 200 252

B785 10 100 785 8 200 252

B503 8 100 503 8 200 252

B385 7 100 385 7 200 193

B283 6 100 283 7 200 193

B196 5 100 196 7 200 193

Table 3: Standard “B” mesh reinforcing details

Reinforcingfabricshouldbeofa“B”meshgrade.Thiscanbeidentifiedbythesizeoftheprimaryandsecondarybars.Primarybarsarespacedat100mmcentresandsecondarybarsareplacedat200mmcentresasindicatedinTable3.


-011-09-010412


6:SUBSTR

UCTU

RES

6.4.3Suspendedtimberfloors

6.4.3.1Durabilityofsuspendedtimberfloors

Topreventthedecayoftimberjoists,thesuspendedtimberfloorshouldbeconstructedinsuchawaythat:

6.4.3.2 Floor joists

Allfloorjoiststobeofasuitabledurabilityandstrengthgrade(minimumC16),beofthecorrectsize,stressgrade,andlaidatthecorrectspecifiedcentresasindicatedonplansandspecifications.Thejoistsshouldhaveconsistentdimensionsandbesecurelynailedtotimberwallplates.

Joistsatthejunctionwiththeexternalandpartywallsshouldbesupportedonsuitablejoisthangersandbeadequatelystruttedatmid-span.

Floorjoistscanbesupportedinternallybysleeperwalls.Sleeperwallsshouldbebuiltofanadequatefoundationorifthegroundisofsuitablebearingstrata,orcanbebuiltoffareinforcedthickenedslabwheredesignedbyaCharteredStructuralEngineer.

6.4.3.3 Concrete over-site

Asuitableoversiteshouldbeprovidedatleast150mmbelowthetimbersuspendedfloor.

Theoversiteshouldbeeither:

• 100mmthickconcreteoversite(Gen3)onwellcompactedhardcore,or;

• 50mmthickconcreteoversiteona1200gdampproofmembranelaidon25mmsandblindingandwellcompactedhardcore.

Forsitesthataresusceptibletogasmigrations,theoversiteshouldincorporategasprotectionmeasuresthathavebeendesignedbyasuitablespecialist.

• Alljoistsandwallplatesareabovethedampproofcourselevel.

• Aminimumvoidof150mmisprovidedbetweenthejoistsandover-site.

• Airbricksareprovidedtogiveadequatecrossventilationtothefloorvoid.

• Joistshaveadequatebearingsanddonotprotrudeintothecavity.

Figure13:Typicalsuspendedtimberfloor


-011-09-010412


6:SUBSTR

UCTU

RES

anglestothejoists.(ThemajoraxisisindicatedontheOSBboardbyaseriesofarrows).

Particleboardsshouldbeeitherscrewedornailedtothejoistsat250mmcentres.Nailsshouldbeannularringshank,whichareatleastthreetimesthe depth of the board.

A10mmexpansiongapshouldbeprovidedaroundtheperimeteroftheflooragainstawallabutment.

Thickness (mm) (chipboard)

Thickness (mm) (OSB)

Maximum span (mm)

Typical nail fixing(mm)

18and19 15mm 450 60mmannularringshank

22 18and19mm 600 65mmannularringshank

Table8:Particlefloorboarding

6.4.3.7 Sound insulation and air tightness

Duetotheconstructionmethods,itismorelikelythatsuspendedtimbergroundfloorswillbemoredifficulttodemonstratesatisfactorylevelsofairtightnessandsoundinsulation.Inensuringthatareasonablelevelofairtightnessandsoundresistanceisachieved,thefollowingprovisionsshouldbeincorporated:

• Alljoiststobesupportedoffproprietaryjoisthangersatthejunctionwithpartywallsandexternalperimeterwalls.

Thecrossflowofairmustnotbeinterruptedbyinternalwallsorlowhanginginsulation.Allinternalwallsmusthaveairbrickstoallowthefreeflowofairorbebuiltusingahoneycombtechnique.

6.4.3.5 Floor boarding or decking

Suitablefloorboardsanddeckinginclude:Tongueandgroovedsoftwoodflooringwithaminimummoisturecontentatthetimeoffixingtobebetween16-20%andinaccordancewithBS1297.Allboardsmustbedoublenailedorsecretnailedtoeachjoistusingnailsthatareatleastthree times the depth of the board. Boards to haveaminimumthickness,asindicatedinTable7.

Finished board thickness (mm)

Maximum centres of joists (mm)

Typicalnailfixing(mm)

15 Max450 45mmlosthead nail

18 Max600 60mmlosthead nail

Table7:Softwoodfloorboarding

6.4.3.6Particlefloorboarding

AcceptableparticleboardsconsistofOrientedStrandboard(OSB)orChipboard.

Chipboardshouldbetongueandgroovedandalljointsglued.Theboardsshouldbelaidsothattheshortestlengthislaidparalleltothespan.OSBboardsshouldbetype3or4toBSEN300.OSBboardsshouldbelaidwithitsmajoraxisatright

6.4.3.4Subfloorventilationrequirements

Topreventdecayingfloorjoists,subfloorventilationmustbeprovidedandgiveafreecrossflowofair.ExternalairbricksshouldbeprovidedintwoopposingwallswhichmeetthefollowingprovisioninTable5

Floor area of building (m2) Minimum ventilation provision (mm2)

40 20,00060 30,00080 40,000100 50,000120 60,000140 70,000160 80,000

Table5:Suspendedtimberfloors-minimumcross ventilation provision

Airbricksshouldbeevenlyspacedalongthetwoopposingwallsthatmeettheventilationprovision.TypicalventilationareasforvarioustypesofairbrickscareareidentifiedinTable6.

Air brick type Dimensions wxh (mm)

Net area (mm2)

Clayairbricksquareholes

225x75 1400

225x150 4300

225x225 6400

Clayairbricklouvered

225x150 2000

225x225 6400

PCVairbrick 225x75 4645

Table 6: Typical air brick net ventilation area capacities (Ventilation rates will vary between different manufacturers)


-011-09-010412


6:SUBSTR

UCTU

RES

PVC225x75mmairbrick.Theventilatedvoidmusthaveaminimumdepthof150mmfromtheundersideofthefloor.

Figure14:Typicalpre-castbeamandblockfloor with DPM

Method 2 - No Damp Proof Membrane

Wherenodampproofmembraneisincorporatedintotheprecastbeamandblockfloor,thebeamandblockfloormustbelaidabovethedampproofcourse.Thefloorvoidbeneaththebeamsshouldbeappropriatelyventedtoensurethatacrossflowofairbetweentwoexternalwallsisachieved.Theminimumareaofventilationshouldequatetoatleast1500mm2permetrerunofexternalwall;thisroughlyequatestoanairbrickevery3mcentresforatypicalPVC225x75mmairbrick.Theventilatedvoidmusthaveaminimumdepthof150mmfromtheundersideofthefloor.Thesolumlevelmustbeatthesamelevelastheexternalgroundlevel.

tosupportloadbearingwalls;allwallsshouldbe built off an appropriate foundation as indicatedinChapter5.

• Asuitablemortarbedisrequiredwhereblockworkbetweenthefloorbeamsbearontoloadbearingwalls,e.g.,perimeterwalls.

• Holesmustnotbemadethroughthefloorbeamsandanyservicepenetrationsshouldpassthroughtheholesmadeinthein-fillblocks,Anygapsaroundservicepenetrationsshouldbefilledwithconcrete(ST3)mixbeforescreeding.

Wherebeamandblockfloorsaretobeinstalledtoareaswithhigherpotentialpointloadssuchasgarages,additionalreinforcingwillberequiredtothescreedtodistributeloadseffectively.Thisreinforcingshouldbeofatleastan‘A’meshqualityandthescreedshouldhaveenoughthicknesstogiveanappropriatedepthofcover.

6.4.4.3 Resistance to ground moisture

Theprecastbeamandblocksubstructurefloorshallbedesignedtopreventwateringress.Therearecommonlytwomethodsofachievingthis:

Method 1 - Damp Proof Membrane

Adampproofmembraneshouldbeprovidedbeneaththescreedorinsulation;thefloorvoidbeneaththebeamsshouldbeappropriatelyventedandensuringthatacrossflowofairbetweentwoexternalwallsisachieved.Theminimumareaofventilationshouldequatetoatleast1500mm2 per metrerunofexternalwall,thisroughlyequatestoanairbrickevery3mcentresforatypical

• Floorboardingtobesealedagainstthewallusingasealantorproprietarytape.

6.4.4 Precastbeamandblockfloors


Alltopsoilandorganicmattershouldberemovedfrombeneaththeprecastsuspendedfloor.Thegroundlevelshouldbeatleastthesameastheexternalgroundlevelunlessthegroundbelowthefloorisfreedraining.Alternatively,aDPMlinkedtotheDPCcanbeprovided.

6.4.4.2Suitabilityofbeamandblockfloors

Allbeamandblockflooringsystemsmusthaveappropriatethirdpartycertificationoraccreditation,whichmeetthefunctionalrequirementofthisChapter.

Themanufacturer’sdetailsandspecificationforthefloormustinclude:

• Structuralcalculationsforthefloorindicatingdepthandcentresoftheprecastfloorbeams.

• Thesuitabilityanddurabilityofwallssupportingthebeamandblockfloor.

• Recommendedblocksforin-fillingbetweenthebeamsincludingcompressivestrengthandthicknessoftheblock.

• Allbeamandblockfloorsshallbeinstalledensuringthatthefollowingstandardsaremet;

• Floorbeamsandblocksaregroutedtogetherusingacement/sandslurrywithamixratioof1:6respectively.

• Thebeamandblockfloorshouldnotbeused


-011-09-010412


6:SUBSTR

UCTU

RES

Figure15:Typicalpre-castbeamandblockfloor without DPM

6.4.4.4 Insulation

Insulationthatistobeprovidedtogroundfloorshouldbeplacedabovethebeamandblock.Insulationshouldbeinstalledinaccordancewithmanufacturer’sinstructionsandbedurableenoughtowithstandfloorloadingsandmoisture.Anumberofinsulationproductsrequireanadditionaldampproofmembranetoprotectthesurfaceoftheinsulation.

contents · chapter 6: substructure contents 6.1 basements 6.2 walls below ground 6.3 damp proofing...

Documents