Building America Special Research Project: High-R ... · Foundations Case Study Analysis Building...

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Building America Special Research Project: High-R Foundations Case Study Analysis

Building America Report - 1003 20 August 2010 Jonathan Smegal and John Straube

Abstract:

Many concerns, including the rising cost of energy, climate change concerns, and demands for increased comfort, have lead to the desire for increased insulation levels in many new and existing buildings. Building codes are improving to require higher levels of thermal control than ever before for new construction. This report considers a number of promising foundation and basement insulation strategies that can meet the requirement for better thermal control in colder climates while enhancing moisture control, health, and comfort.

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BuildingAmericaSpecialResearchProject

HighRFoundationsCaseStudyAnalysis20100820

JonathanSmegalMAScJohnStraube,PhD,P.Eng

BuildingScienceCorporation30ForestStreet

Somerville,MA02143

www.buildingscience.com

Building Science Corporation 1 www.buildingscience.com 30 Forest St. Somerville, MA 02143

TableofContentsA. Introduction ...........................................................................................................................................................................................4

1.Objective...................................................................................................................................................................................................4

2.Scope ..........................................................................................................................................................................................................5

3.Approach..................................................................................................................................................................................................5

B. Analysis ....................................................................................................................................................................................................5

1.Wallassembliesreviewed ................................................................................................................................................................5

2.AnalysisCriteria....................................................................................................................................................................................5

2.1ThermalControlandHeatFlowAnalysis ..........................................................................................................................7

2.2HygrothermalAnalysis ........................................................................................................................................................... 16

2.3EnclosureDurability ................................................................................................................................................................ 41

2.4Buildability................................................................................................................................................................................... 41

2.5MaterialUse ................................................................................................................................................................................. 41

2.6Cost 42

2.7OtherConsiderations............................................................................................................................................................... 42

C. Results ................................................................................................................................................................................................... 43

1.Case1:UninsulatedFoundationWallsandSlab................................................................................................................. 43

1.1ThermalControl......................................................................................................................................................................... 43

1.2MoistureControl........................................................................................................................................................................ 43

1.3ConstructabilityandCost....................................................................................................................................................... 44


2.Case2:CodeminimumR10continuousinsulation........................................................................................................... 45

2.1ThermalControl......................................................................................................................................................................... 45




3.Case3:R13fiberglassbattina2x4framedwall ................................................................................................................ 47

3.1ThermalControl......................................................................................................................................................................... 47




4.Case4:1”XPS,2x4woodframedwallwithfibreglassbatt ........................................................................................... 49

4.1ThermalControl......................................................................................................................................................................... 49





5.Case5:2”XPS,2”foilfacedpolyisocyanurate ..................................................................................................................... 51

5.1ThermalControl......................................................................................................................................................................... 51




6.Case6:3.5”2.0pcfclosedcellspraypolyurethanefoam ............................................................................................... 53

6.1ThermalControl......................................................................................................................................................................... 53




7.Case7:6”0.5pcfopencellsprayfoam................................................................................................................................... 55

7.1ThermalControl......................................................................................................................................................................... 55




8.Case8:2”XPS,2x4framingwithfibreglassbatt ................................................................................................................ 57

8.1ThermalControl......................................................................................................................................................................... 57




9.Case9:2”Polyisocyanurateinsulation,2x4framingwithcellulose.......................................................................... 58

9.1ThermalControl......................................................................................................................................................................... 58




10.Case10:6”0.5pcfsprayfoamwith2x4framingoffset2.5”fromconcrete ........................................................ 59

10.1ThermalControl ...................................................................................................................................................................... 59

10.2MoistureControl ..................................................................................................................................................................... 59

10.3ConstructabilityandCost .................................................................................................................................................... 60

10.4OtherConsiderations ............................................................................................................................................................ 60

11.Case11:4”XPSinsulationontheexterioroffoundationwall................................................................................... 60

11.1ThermalControl ...................................................................................................................................................................... 60




12.Case12:4”XPSinsulationinthecenteroffoundationwall ....................................................................................... 61


12.1ThermalControl ...................................................................................................................................................................... 62




13.Case13:InsulatedConcreteForms,2”XPSoninteriorandexterior ..................................................................... 63

13.1ThermalControl ...................................................................................................................................................................... 63




14.Case14:2”XPS,2x6framingwithfibreglassbatt ........................................................................................................... 64

14.1ThermalControl ...................................................................................................................................................................... 64




15.Case15:4”PIC,2x6framingwithfibreglassbatt............................................................................................................ 65

15.1ThermalControl ...................................................................................................................................................................... 65




D. Conclusions.......................................................................................................................................................................................... 67

E. FutureWork........................................................................................................................................................................................ 69

F. WorksCited ......................................................................................................................................................................................... 70


A. Introduction

Manyconcerns,includingtherisingcostofenergy,climatechangeconcerns,anddemandsforincreasedcomfort,haveleadtothedesireforincreasedinsulationlevelsinmanynewandexistingbuildings.Buildingcodesareimprovingtorequirehigherlevelsofthermalcontrolthaneverbeforefornewconstruction.Thisreportconsidersanumberofpromisingfoundationandbasementinsulationstrategiesthatcanmeettherequirementforbetterthermalcontrolincolderclimateswhileenhancingmoisturecontrol,health,andcomfort.

The2009IRC(TableN1102.1)and2009IECC(Table402.27)requirebasementsinDOEclimatezonesfourandgreatertorequireacontinuouslayerofR10insulationorR13inaframedwall.HighRbasements,forcoldclimates,inthisreportarewallsthatapproachorexceedatrueR‐valueofR20.Inawarmerclimate,thatdoesnotrequirebasementinsulation,high‐Rmaybeconsideredless.

Basementsarestereotypicallycool,damp,mustysmellingareasofthebuildingthatwerehistoricallyunfinished,unoccupiedandusedmostlyasstorage.Moreandmoreoften,peoplearefinishingtheirbasementstoincreasethelivingenvironmentandfrequentlythebasementistransformedintoamediaroom,bedroom,orextralivingroom.Thesenewenvironmentsrequiregreatercontrolofbothheatandmoisturetoprovideahealthylivingenvironmentwithminimalrisktoequipmentandfinishes.

Asuccessfulfoundationwillperformthefollowingtasks

• Holdthebuildingup• Resistsoilpressures• Keepthegroundwaterout• Keepthesoilgasout• Keepthewatervaporout• Allowanywatervaporinthewalltoleave• Keeptheheatinduringthewinter• Keeptheheatoutduringthesummer

Basementfailuresoccuroftenduetoflooding,orcondensation,bothofwhichmayresultinmouldordustmiteproblems.However,buildingphysicsandextensivefieldexperiencehasshownthatthemajorityofallbasementmoistureandcomfortissuescanbeavoidedbyproperdesignandmaterialselection.

Thisstudycomparesoveradozenbasementandfoundationenclosuredesignsincludinghistoricalconstructionstrategies,codeminimumconstructionandhighlyinsulatedconstruction.Thisreportdemonstratesthroughcomputerbasedsimulationsandfieldexperience,differencesinenergyconsumption,thermalcontrol,andmoisturerelatedissues.

ThisstudyisanextensionofthepreviousBuildingAmericastudyofHighRwallassemblies(StraubeandSmegal2009),tocontinuetoimprovetheoverallbuildingenclosureandachievegreaterenergysavings.

1. OBJECTIVE

Thegoalofthisresearchistofinddurable,costeffectivebasementinsulationsystemthatcanbeincludedwithotherenclosuredetailstohelpreducewholehouseenergyuseby70%.Thisreportwillcompareavarietyofbasementandfoundationinsulatingstrategiesandpresenttheiradvantagesanddisadvantagesaccordingtoseveralcomparisoncriteria.


2. SCOPE

Thisstudyislimitedtobasementandfoundationsystemsforcoldclimates.Apreviousstudywasconductedforwallsystemsandfurtherstudiesshouldbeconductedtoaddressroofsandattics.Ingeneral,onlycoldclimatesareconsideredinthisreportsinceenclosuresincoldclimatesbenefitthegreatestfromahighlyinsulatedbuildingenclosure,butimportantconclusionscanalsobedrawnforotherclimatezones.

3. APPROACH

Thequantitativeanalysisforeachwallsystemisbasedonathree‐dimensionalenergymodelingprogramandaone‐dimensionaldynamicheatandmoisture(hygrothermal)model.Minneapolis,MNinIECCclimateZone6wasusedastherepresentativecoldclimateformostofthemodeling,becauseofcoldwinterweatherandfairlywarmandhumidsummermonths.

B.Analysis 1. WALL ASSEMBLIES REVIEWED

Becausethereareanumberofvariablesforeachpossiblewallsystemdependingonthelocalpractices,climate,andarchitectorgeneralcontractorpreferences,anattemptwasmadetochoosethemostcommonwallsystemsandmakenotesaboutotheralternativesduringanalysis.Thislistofchosensystemsisexplainedinmoredetailintheanalysissectionforeachwallsystem.

• Case1:Un‐insulatedBasement• Case2:CodeminimumR10continuousinsulationwithpoly• Case3:3.5inchesfiberglassbattin2x4SPFwoodframedwallwithpoly• Case4:1inchXPS+3.5inchesfiberglassbattin2x4SPFwoodframedwall• Case5:2inchesXPS+2inchespolyisocyanuratewithR10underslab• Case6:3.5inches2.0ccpcfsprayfoamwithR10underslab• Case7:6inches0.5ocpcfsprayfoamwithR10underslab• Case8:2inchesXPS+3.5inchesfiberglassbattin2x4SPFwoodframedwallwithR10underslab• Case9:2inchespolyisocyanurate+3.5inchescellulosein2x4SPFwoodframedwallwithR10under

slab• Case10:6inches0.5ocpcfsprayfoaminoffset2”x4”SPFwoodframedcavitywithR10underslab• Case11:4inchesXPSonexteriorofbasementwithR10underslab• Case12:4inchesXPSincentreoffoundationwallwithR10underslab• Case13:ICFwallwith4”XPSandR10underslab• Case14:2inchesXPS+5.5inchesfiberglassbattin2”x6”SPFwoodframedwallwithR10underslab

2. ANALYSIS CRITERIA

Acomparisonmatrixwillbeusedtoquantitativelycompareallofthedifferentbasementinsulationstrategies.Avaluebetween1(poorperformance)and5(excellentperformance)willbeassigned,uponreviewoftheanalysis,toeachofthecomparisoncriteriaforeachwall.AnemptycomparisonmatrixisshownbelowinTable1asanexample.


Table 1: Criteria comparison matrix

Thecriteriascoreswillbesummedforeachinsulationstrategy,andthewallswiththehighestscoresarethepreferredoptionsassumingallofthecomparisoncriteriaareweightedequally.Itisalsopossibletoweightthedifferentcomparisoncriteriaasymmetricallydependingonthecircumstancessurroundingaparticularwalldesign.Theweightingsforeachwallwillfallbetween1(leastimportant)and5(mostimportant).Theweightingismultipliedbythecomparisoncriteriascoreandaddedtootherweightedvalues.Anexampleoftheweightedconclusionmatrixwillbeshownintheconclusionssectionofthisreport.

Oneofthebenefitsofusingacomparisonmatrixisthatitallowsaquantitativecomparisonwhensomeofthecriteria,suchascostmaybepoorlydefinedorhighlyvariable.Forexample,eventhoughtheexactcostsofdifferentinsulationsmaybeuncertain,fiberglassbattinsulationisalwayslessexpensivethanlowdensity(0.5pcf)sprayfoamwhichislessexpensivethanhighdensity(2.0pcf)sprayfoam,sothesesystemscanberankedaccordinglyregardlessoftheactualcosts.

Eachofthecriteriaaredescribedindetailbelow.


2.1 Thermal Control and Heat Flow Analysis

TheHeatflowandenergyanalysisofeachbasementsystemwasconductedwithBasecalc,developedbyCanmetENERGYandbasedontheNationalResearchCouncilofCanada’sMitalasmethod.Mitalasusedmainframecomputerstoperformfinite‐elementanalysesofalargenumberofbasementsandanalyzedtheresultstoproduceaseriesofbasementheat‐lossfactors,whichwerethenpublishedasareference(Mitalas1983).

AusercanapplytheMitalasmethodbyusingthecorrectheat‐lossfactorsfromthepublishedtablesandperformaseriesofcalculationstopredictheatandenergylosses.Basecalcincorporatesthefinite‐elementapproachMitalasusedtogeneratetheheat‐lossfactors.DuringthisstudyananalysisspreadsheetmodelwasconstructedusingtheMitalasmethodandcomparisonsoftheresultsbetweentheanalysisspreadsheetandBasecalchavebeenconducted.

TheBasecalcsoftwareisarelativelysimplemenudrivenprogramthathasmanyoptionsforconstructionstrategies,insulationplacementandsiteconditions(Figure1).

Figure 1 : Screen Capture showing inputs for Basecalc

SomeassumptionsweremadeforalloftheBasecalcanalysistoensurecomparisonwaspossiblebetweenresultingsimulations.Theenergycalculatedisonlyforthesespecificcases,andmodifyinganyofthevariablesmaychangetheresultingenergyrequirements.Theseassumptionsarelistedbelow:


• AllsimulationswererunforMinneapolis/St.PaulMN,dataincludedinBasecalc• Basementinteriorheight‐distancefromtopofslabtotopoffoundationwall2.44m(8ft)• Depth(belowgradefoundation)–distancefromtopofslabtosurfaceofground,2.13m(7ft)• Width‐exteriorofstructuralwalltoexteriorofstructuralwall,10m(32.8ft)• Length–exteriorofstructuralwalltoexteriorofstructuralwall,15m(49.2ft)• Basementwallarea–118m2(1270ft2)• Basementfloorslabarea–140m2(1506ft2)• Basementperimeter–48.5m2(159ft2)

InBasecalc,therimjoistisnotconsidered,(butthiswasanalyzedinpastresearch,StraubeandSmegal2009),butthermalbridgingacrossthetopofthefoundationwallisconsidereddependingonabovegradewallconstruction.Forexample,oneofthemostcommonthermalbridgesintypicalresidentialconstructionistheexteriorabovegradebrickcladdingsittingontheoutsideedgeofthefoundationwall.

Figure 2 : Typical construction thermal bridging through foundation and brick cladding ThisthermalbridgingcanbetakenintoaccountinBasecalc.Forallsimulationsinthisstudy,theabovegradecladdingwasassumedtobenon‐brickveneer.Intypicalconstructionwithbrickveneer,thereisasignificantthermalbridgebetweentheinteriorandexteriorwhenthebrickcladdingisinstalledontheexterioredgeoftheconcretefoundationwall.Itwasassumedthattherewasnosignificantthermalbridgeatthetopofthefoundationwall.

AlloftheBasecalcresultsarepresentedinunitsofMBtus.Forclarification1MBtuanditsequivalentenergyinothercommonunitsofmeasureareshowninTable2.

Table 2 : Conversion of 1 MBtu to Other Common Energy Units MillionBtu’s(MBtu’s) 1

Btu’s 1,000,000

Therms 10

Megajoules 1,057

Kilowatthours 293.6


Acommonwaytoexplainenergysavingstohomeownersisoftenindollarssavedsincethevalueofadollariswellknownandcanbecomparedtootherdesigndecisions.Unfortunately,pricesvaryconsiderablyacrossthecontinentforheatingenergy,andalsovarydependingonthetechnologyusedforheating,whetheritbeelectricity,naturalgas,oil,etc.Foranalysispurposes,ifcostcomparisonsareuseditwillalwaysbeforelectricheatingat15centsperkilowatthour($44/MBtu).Asacomparison,naturalgasat$1.50/thermburntina90%efficientfurnacecosts$16.70/MBtu.Thecostofenergyislikelytorise,eventhoughtherateofincreaseisunknown,sodollarsavingsarelikelytobehigherinthefuture.

2.1.1. Building Code Requirements Accordingtothe2009IECCinclimatezones4orhigher,thebuildingcoderequiresaminimumofR10continuousinsulation(e.g.fiberglassrollbatt)orR13discontinuous(e.g.framedwallwithR13fiberglassbatt)unlessitisanunconditionedbasementandtheflooroverheadisinsulatedinaccordancewithIRCSectionsN1102.1andN1102.2.6.AddingthisrequiredamountofinsulationmakesasignificantdifferencefromanenergyperspectiveasshowninFigure3,butmaynotadequatelyaddressthecomfort,moistureandhealthconcernsthatoccurinbasements.Case1inthisstudyisanun‐insulatedbasementasmanysuchcasescanbefoundinexistingbuildings,andCases2and3aretypicalofcodeminimumbasementsbuiltinmanycoldclimates.

Aninitialanalysiswasconductedtodeterminetheeffectsofdifferentamountsofinsulationandstrategiesonthetotalheatlosspriortoanalyzingthevariouswallsystems.Figure3showstheimprovementsinannualenergylossbyinsulatingthefullheightofthebasementwallwithdifferentinsulationvaluescomparedtoanun‐insulatedbasement.ThemostsignificantimprovementisachievedbyaddingthefirstR5,whichshowsthataddinganyinsulationcouldhelpwithenergylosses.IncreasingtheinsulationtoR10whichisthecodeminimumasacontinuousinsulationresultsinapredictedenergysavingsof31.2MBtus(savingsof$1372/yearbasedon$0.15/kWhror$44/).Theenergysavingsshouldbeconsideredwhendeterminingthecostofaddinginsulation,andwhetherornotitiscosteffective.

Thebasementwallhasanareaofapproximately1270ft2andR5foaminsulationcostsapproximately50‐75¢/sfplusinstallation.UsingR10rigidfoaminsulationovertheentirebasementinthiscasewouldcostintherangeof$1270to$1905,andwouldsaveapredicted$1372/year.

Figure3alsoshowsthepredictedenergysavingsiftheslabisinsulatedwithR10belowtheslab.Intheun‐insulatedcasethereisanimprovementofHeatingSeasonEnergyLossof1.3MBtus,andintheR20insulatedwallcomparisontheimprovementisslightlyimprovedwithunderslabinsulationat1.5MBtus.However,themostimportantaspectsoftheunderslabinsulationarenotshownonthisgraph.Comfortlevelsandmoisturerelatedissuesincludingdampnessandmustyodors,andstorageofmoisturesensitivematerialsonthefloorwilldecreaseifunderslabinsulationisused.Insomecaseswhenradiantfloorheatingisused,R20orgreaterunderslabinsulationisnecessarytoreducetheheatlosstotheground.

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Figure 3 : Reduction in Energy Loss with the Addition of Full Height Foundation Wall Insulation



Figure 4 : Comparison of Different Underslab Insulation Techniques with R10 on foundation walls



Figure 5 : Energy Savings From Thermal Break Insulation Between Concrete Footing and Slab

2.1.2. Case Study – Westford Prototype House


Figure 6 : Basement Floorplan of BA Westford Prototype House H2KwasalsousedtosimulatetheheatingenergylossesoftheWestfordprototypehouseanditwaspredictedthat6.96MBtusarelostbelowgrade,and2.36MBtusarelostabovegradeinthebasementforatotalbasementheatlossof9.32MBtusinayear.H2Kalsopredictedthetotalhouseheatingenergylossesof27.16MBtus,verysimilartotheEnergyGaugevalue.

Inthisstudy,Basecalcwasusedtodeterminethetotalannualenergylossthroughthebasementis7.1MBtuswhichissimilartotheH2Kvalue.BymodifyingsomeoftheinsulationvaluesinthebasementusingBasecalc,theeffectonthetotalhouseenergycanbeseentodetermineifincreasesininsulationvaluesarecosteffective.

Table3showstheeffectonthepredictedwholehouseheatingenergylossesbychangingtheamountofinsulationundertheslab.

Table 3 : Effects of Whole House energy by changing Underslab Insulation


PredictedBasementEnergyLosses[MBtu]

ChangeinBasementEnergyLosses[MBtu]

ChangeinWholeHouseEnergyLosses[%]

RemovingUnderslabinsulation 8.4 1.3 4.8%

R10underslab 7.1 0 0

R20underslab 6.2 ‐0.9 ‐3.4%

R30underslab 5.7 ‐1.4 ‐5.0%

Table3showsthat1.3MBtusweresavedbyaddingR10underslabinsulation,asavingsofalmost5%oftheentirehouse’sheatingenergylosses.Astheunderslabinsulationisincreased,thechangestotheentirehouse’sheatingenergylosesbecomemuchlesssignificant.Tosaveanotherapproximately5%oftheentirehouse’sheatingenergylosses,anotherR20isrequiredabovetheoriginalR10insulation.

Table4showstheeffectonthepredictedwholehouseheatingenergylossesbychangingtheamountofinsulationonthefoundationwalls.

Table 4 : Effects of Whole House Energy by Changing Foundation Wall Insulation

PredictedBasementEnergyLoses[MBtu]

ChangeinBasementEnergyLosses[MBtu]

ChangeinWholeHouseEnergyLosses[%]

R10codeminimumfoundationwallinsulation 10.4 3.3 11.9%

R26foundationwallinsulation 7.1 0 0

R40foundationwallinsulation 6.2 ‐0.9 ‐3.4%

Table4showsthat12%oftheheatinglossesofthehousearesavedfromincreasingthefoundationwallinsulationfromthecodeminimumR10toR26,whichisasignificantportionoftheheatingenergylosses.Thisshowsthatitcanbecosteffectivetoinsulatethebasementincoldclimatesbasedonheatingenergyalone,withoutconsideringallofthemoisturerelatedbenefits.

ByincreasingtheinsulationanotherR13toR40,resultsinonlya3.4%decreaseintheheatingenergylossesfortheentirehouse.At$1.20/sf,thisinsulationwouldcost$1062,andwouldsave0.9MBtu/year.

2.1.3. Basement Wall Analysis ThefourteendifferentwallslistedpreviouslyweresimulatedinBasecalc,andtheheatingenergylosseswereestimated.SomeoftheproposedwallsystemshadcontinuousinsulationandtheR‐valueswereassumedtobeequaltotheirrating.Otherproposedwallsystemswereframedorfurredouttotheinteriorandinsulatedwithcavityinsulation.Theframingmaterialsintheseassembliesactasathermalbridgebypassingtheinsulation.Fortheframedwalls,theparallelpathmethodwasusedtocalculatetheR‐value,whichisaratiooftheRvaluethroughtheframingtotheR‐valuethroughthecenterofthestudspace,assumingaframing


spacingof24”oncenter.Alsotakingintoaccountthegypsumwallboardandsurfacefilm,thethermalbridgingoftheframingdidnotsignificantlyaffecttheR‐value,infact,insomecasesthecalculatedparallelpathR‐valuewasslightlyhigherthantheinstalledinsulationR‐value.

Underslabinsulationandaslab‐edgethermalbreakwereonlyincludedinsimulationsforCases5to14,sinceitisunlikelythatbuilderswillinstallunderslabinsulationwhenonlyminimalfoundationwallinsulationispresent.

Figure 7 : Comparison of Heating Energy Losses for all Cases Asstatedpreviously,evenR10foundationwallinsulationshowedasignificantamountofenergysavingscomparedtoun‐insulatedbasements.However,insomecases,increasingtheinsulationincreasestheriskformoisturerelatedproblemsthatwillbeanalyzedintheHygrothermalAnalysissection.

Therangeofenergylossfortherecommendedfoundationinsulationstrategies(Cases5–14)is14.8to19.43MBtusperyearforthespecifichouseexamined.Cases5‐10,13,and14haveessentiallyidenticalperformance.Thevalueofthesesavingsdependsonthecharacteristicsofthehouse,theclimatezone,thetypeofenergyusedanditsassociatedcost.

ThebestperformingfoundationinsulationstrategiesfromaheatlossperspectiveareCase14(2”XPS,5.5”fibreglassbatt)andCase9(2”PIC,3.5”cellulose),butthereareseveralothersthatperformverywell.TheadvantagesanddisadvantagesofthevariousinsulationstrategieswillbecomparedfurtherintheAnalysissection.


2.2 Hygrothermal Analysis

Moisture Balance

Assessingmoisturerelateddurabilityrisksinvolvesthreedifferentmoistureprocesses;wetting,dryingandmoistureredistribution.Thesethreeprocessesincombinationwiththesafestoragecapacityofeachcomponentwilldeterminetheriskofmoisturedamagetoabasementassembly.Thisreportonlyincludesabriefoverviewofthewettingmechanisms(moredetailbyJosephLstiburek2006).

Therearefourmainwettingmechanismsinfoundationsandbasements.Theyare:

Bulkwaterpenetrationfromtheexterior Capillarywickingor“risingdamp” Vapordiffusionandairleakagecondensation(fromexteriororinterior) Plumbingissuesontheinterior(notconsideredinthisanalysis)

Thegreatestamountofdamageintheshortesttimewillbecausedbyabulkwaterpenetrationfromtheexteriororinteriorplumbingrelatedissues.Thebeststrategytoavoidwateringressintothebasementfromtheexterioristodrainallofthecomponentsawayfromthebuildingincludingthesiteandtheexteriorofthefoundation(Figure7).Sometimesitisunavoidabletohaveliquidwaterincontactwiththefoundationandotherstrategiesmustbeusedincludingexteriordrainagematsandsumppumps.Inolderbuildings,foundationwallsmayhavebeenconstructedofrubbleorstoneandoftenallowwaterdirectlythroughthefoundationwallintherainyorthawseason.Ensuringbasementdrainsareproperlylocatedandthattheyareclearofobstructionswillminimizefloodingcausedbyinteriorplumbingissues.Thisstudydoesnotdealspecificallywithretrofitstrategies,butthepossibilityofuseinretrofitapplicationswillbementionedforanyrelevantinsulationstrategies.AdditionalinformationregardingtheretrofitofbasementsisavailableinPettit(2005).


Figure 8 : Drainage details to minimize foundation moisture issues Thesecondsourceofmoistureinthebasementenclosureismoisturetransportedfromwetsoilbycapillarywicking.Thephysicalcharacteristicsandporesizeofconcrete(10–1000nm)allowittowickmoisturequiteeffectivelyagainsttheforceofgravity,oftenwithsuctionpressuresof100kPato10MPa(StraubeandBurnett2005).Themostcommonsourceofwaterforcapillaritywickingisthefooting.Inmanycasesamoisturebarriersuchasdamp‐proofing,oradrainagemembrane,orbothareappliedtotheexteriorofthewallminimizingtheriskofcapillaryabsorptionthroughthefoundationwall.Thefloorslabisoftenpouredovergravelwhich,ifithasnofines,actsasacapillarybreakandshouldbedrainedtotheexteriordrainagetile.Inmanyhousefoundations,thereisnocapillarybreakinstalledontopofthefooting,andthereforewaterdrawnintothefootingisalsowickedfurtherupthefoundationwall.Inatypicalbasement,theliquidwaterisdrawntothesurfacesoftheconcretefoundationwall(Figure9),itwillevaporateanddrytotheinteriorortotheexteriorasenvironmentalconditionspermit.Ifdryingishinderedbyapolyethylenevaporbarrier,elevatedrelativehumiditiesmayoccurnearthewallsurfaceorwithinthewallcavityeventuallyresultinginmouldandothermoisturerelatedissues.

Ashomeownersfinishandinsulatetheirbasementspaces,apolyethylenevaporbarrierisofteninstalledtomeetthelocalbuildingcode.Somebuilderswhohavelearnedfrompastexperiencewillremoveasectionofthepolyethylenevaporbarrieratthebottomtoavoidmoldproblemsthathavebeendiscoveredinmanybasements.Removingthebottomsectionofthevaporbarrierallowsliquidwaterwickedupthefootingandintothefoundationwalltodrytotheinteriorspace.Thepreferredsolution,ofcourse,wouldbetoinstallacapillarybreakbetweenthefootingandfoundationwallduringtheoriginalconstructionprocesstostop


moisturefrombeingwickedintothefoundationwall.Alternatively,amoisturetolerantinteriorfoamlayercanreducetheflowtotheinteriorsufficientlytoavoiddamage(ifnoadditionalvaporbarrierisadded).

Figure 9 : Capillary rise through basement footing Thethirdsourceofmoistureinthebasementenclosureiscausedbyvapordiffusion.Asdiscussedwithcapillarityabove,vapordiffusionoccursfromtheinteriorsurfaceoftheconcreteafterwateriswickedupthefoundationwall.Vapordiffusioncanalsooccurthroughfloorslabifnovaporbarrierisinstalledbelowtheslab.Therateofvapordiffusionisslow,butstillmaycausedurabilityissueswithvaporimpermeableflooringsinstalledwithwaterbasedadhesives,aswellasincreasingthemoistureloadinthebasement,whichcancontributetothecommondamp,mustyodour.Vapordiffusionthroughtheslabcanbevirtuallyeliminatedbyinstallingavaporcontrollayer(6milpolyethylene,boardfoaminsulationorsprayfoam)undertheslab.Interiormoisturevaporcouldalsobeanissue,especiallyinlatespringandearlysummerastheenvironmentalrelativehumidityincreasesbuttheconcretefoundationtemperaturesarestillcoolerbecauseoftheseasonaltemperaturelagoftheearthandthermalmass.

Vapordiffusiondryingoftheconcretecanlastforseveralyearsuntiltheconcretefullyhydrates,evenifothersourcesofmoistureareeliminated.Ifthereisnomoisturebarrierontheexterioroftheconcrete,thentheconcretewillneverdrycompletelyandwatervaporwillalwaysbepassingintoandthroughtheconcrete.

Dryingisimportantsincenearlyallbuildingenclosureswillexperiencewettingatsomepoint.Inabove‐gradefoundationwalls,thereisdryingpotentialtoboththeinteriorandexterioriftheenclosuredesignallows.Belowgrade,however,dryingcanonlyoccurtotheinteriorsincetheexteriorsurfaceofabelowgradewallisatessentiallyat100%humidityallyearround.

Thesafestoragecapacity(balanceofwettinganddrying)ofanindividualmaterialorenclosuresystemisfundamentaltogoodbuildingdesign(Figure9).Itisrarelyeconomicaltobuildanenclosurewithnoriskofwettingbutmanagingtheriskisimportant.Inanybuildingenclosure,buildingmaterialsshouldbechosen


basedonmoisturetolerancethatcorrelatetotheriskofmoistureintheenclosure.Inallcasesdryingshouldbemaximized,andattentiontogooddesigndetailsshouldbeused.

Figure 10 : Moisture balance

Manyhouseshavedamp,mustysmellingbasementsthatareuncomfortable,andcanbeunhealthy.Historically,peopledidnotfinishtheirbasementsintolivingspacessoitwasnotasmuchofaconcern,butnowbasementsarebeingconvertedtolivingareas,entertainmentcentresandbedrooms,sohealthandcomfortareasmuchaconcernasforabove‐gradespace.

Afoundationshouldcontroltheamountofliquidwaterandwatervaporenteringtheinteriorspacefromtheexteriorenvironment.Thisstudyassumesdrainagedetailshavebeenconstructedcorrectlytolimittheexposureoftheexteriorofthefoundationtoliquidwater.Therearemanydifferentstrategiestoensurewaterisdrainedawayfromthefoundation,butallsystemsrequireproperlydetaileddrainagealongthefoundationfootingtoremovestandingwater.Thefoundationwallneedstohaveadrainageplanethatdirectsbulkwatertothisfootingdrain.Often,adrainagemembraneisinstalledagainsttheexteriorofthefoundationwalltoperformasbothliquidwaterandwatervaporbarrier.Thedrainagemembraneisrippledorcorrugatedandformsaspacebetweenthemembraneanddampproofedconcretefoundationwall,allowinganywateragainstthefoundationtodraintothedrainagetile.Thisensuresthatthefoundationdoesnotexperienceanyliquidpressurehead.

Eveninaridclimates,thegroundisverycloseto100%relativehumidity,sothatthebelowandabovegradeportionsofafoundationwallexperiencedifferentmoistureandtemperatureregimes.Atthebottomofthebasementwall,thevapordriveistotheinteriorfortheentireyear,andthetemperatureisrelativelystable.Theabovegradeportionofthefoundationwallisverydifferentfrombelowgrade:thevapordriveiscycleddailythroughenvironmentalvariationsofprecipitation,windandsun.

Thehygrothermalsimulationsinthisstudydonotconsiderliquidwateruptakebycapillarityintothefootingandfoundationwall,onlyvapordiffusion.Itisimportanttorecognizethatwaterisoftenwickedupthroughthefootingintotheconcretewall.Oncetheliquidwaterreachestheinteriororexteriorofthebasementwall,itmustbeevaporatedtowatervaporandtravelsbyvapordiffusion.Sincetheexteriorofthefoundationisalreadycloseto100%relativehumidity,themoisturecannotdrytotheexterioranditcanonlyevaporatetotheinside,whichaddstothemoistureloadattheinsulationlayer.Waterthatiswickedthroughthefootingcanbestoppedbyapplyingacapillarybreakbetweenthefootingandthefoundationwall.Therearebothliquidandsheetappliedcapillarybreaksthatwilldecreasethemoistureloadintothefoundationwallandintotheinteriorenvironment.


Sincethefoundationwallbelowgradeisunabletodrytotheexteriorandtherecanbeasignificantamountofmoisturepresentintheconcrete,intuitively,thevapordrivesshouldbeallowedtodrytotheinteriorandapolyethylenevaporbarriershouldnotbebuiltintotheinteriorofthewoodframedwall.Unfortunately,buildingcodeshaveoftenspecifiedpolyethylenevaporbarriersontheinteriorofframedwallsinfinishedbasementsandthesewallswillbeanalyzedtounderstandwhytheyoftenhaveseriousmoisturerelatedproblems.

Thehygrothermalsimulationsconductedforthisstudyareaonedimensionalapproximationofthehygrothermalbehaviourofeachwallsystem.Inrealitytherearetwoandthreedimensionalinteractionssuchasheattransferupanddowntheconcretefoundationwallaswellasconvectiveloopingandmoisturetransportthroughairandvaporpermeableinsulations.

BoundaryConditions

TheWUFIsimulationswereconductedinthreepartsbecauseofthedifferenthygrothermalregimesatthetopabovegradeportion,middleandbottombelowgradeportionsofthewall.TheexteriorbelowgradetemperaturesusedforhygrothermalsimulationswerebasedonmonitoringofgroundtemperaturesinSt.PaulMNasshowninFigure11.TheabovegradetemperaturesforMinneapolisareincludedintheweatherdataforWUFI.


Figure 11 : Monthly temperature variation with soil depth, St.Paul, MN (Bligh 1975) Therelativehumidityoftheexteriorforboththemidheightandbottomofthefoundationwallweresetat99.9%.Inthesesimulations,onlyvapordiffusionfromboththeinteriorandexteriorweresimulatedanditwasassumedthatthefoundationwallandslabwerenotincontactwithliquidwater.Iftheconcreteisincontactwithliquidwater,whichisnotuncommon,especiallyatthefooting,capillarywickingwilloccurandsignificantlyincreasethemoistureloadtothesurfaceoftheconcretenotonlyatthebaseofthewallbutfurtherupaswell.Thiswouldsignificantlyincreasethemoistureloadsabovethepredictedvalueswherethereisnotcapillarybreakinstalledinthefoundationenclosuresystem.

Interiortemperatureandrelativehumiditieswerechosentorepresentaslightlyhigherthanaveragemoistureloadforacoldclimatehouse(Figure12).Theseboundaryconditionsweresimulatedfor10yearstoensurethatthefoundationsystemwasatequilibriumwithboththeexteriorandinteriorenvironments.


Figure 12 : Interior Temperature and Relative Humidity for Hygrothermal Simulations

2.2.1. Wintertime Condensation

Inabovegradewalls,wintertimeairleakageandvaporcondensationareconcernsincoldclimates.Inthebasement,thebelowgradefoundationwallisoftenwarmerthantheexteriorenvironmentinthewinterduetotheheatsinkoftheground,andthethermallymassivestorage.Thismeansthatwintertimecondensationislessofaconcernonthefoundationwallitself.Intheabovegradeportionofthebasementwall,therecanbecondensationasshowninthefollowinghygrothermalanalysis.

Ofgreaterconcernistheearlysummerwhenthefoundationwalliscoolerthantheexteriorenvironmentandoftentherelativehumidityintheenvironmentcanbequitehigh.Iftherelativehumidityincreasesinthebasement,thiscouldresultincondensationandelevatedhumiditiesatenclosuresurfacessuchasonthewallsandfloor.Inbasementswithacarpet,theconcreteslabisslightlyinsulatedfromtheinteriorwarmthandhigherrelativehumiditiesarepossiblesincethecarpetisvaporpermeable.

2.2.2. Summer Inward Vapor DrivesAtthetopofthefoundationabovegradewallthereispotentialforinwardvapordrivesbecauseitissubjectedtothewarmsummertimetemperaturesandsolardrives.Thiswillonlyoccurwherethewallisheatedsufficientlytodrivethevaporintotheenclosure,andisevidentinsomewallassembliesinthehygrothermalanalysis.

Polyethylenesheetbondedtobattinsulationhastypicallybeentheconstructionstrategyusedforinsulatingcoldclimatebasementsinthepast,butnow,withincreasedunderstandingaboutthemoisturephysicsof


basementsandbelowgradewalls,theIRC(InternationalResidentialCode)statesthatClassIandIIvaporretardersarenotrequiredonanybelowgradewallorbasements(IRC2009TableR601.3.1).

Someinsulationsinstalleddirectlyagainstthefoundationareeffectivevaporcontrollayersandinsulationlayersasshowninthehygrothermalanalysis.

2.2.3. Wall DryingBelowgradewallsexperienceelevatedrelativehumiditesontheexteriorandthusmustdrytotheinterioratalltimes.Theabovegradeportionofthefoundationwallcandrytoeithertheinteriororexteriordependingonwallconstruction,butitisrecommendedthattheentirebasementwallbeabletodrytotheinterior.Insomecases,lowerpermeancecoatingsmayberequiredbutaClassIorIIvaporcontrollayershouldbeavoided.

2.2.4. Case 1 Un-insulated Figure13showsthemoisturebehaviorofanun‐insulatedbasementwall.Predictedrelativehumiditiesatthesurfaceoftheconcretewallshowthereisverylittlepotentialforcondensation,onlyatthecoldesttimeofyearonthenorthorientationwithnosolarenergydoestheinterioroftheconcretegetcoldenoughtocondensewatervaporfromtheinteriorenvironmentwiththesimulatedinteriorrelativehumiditylevels.

Figure 13 : Predicted RH at the Interior Surface of the Concrete Foundation Wall for Case 1 ThepredictedsurfacetemperaturesofthefoundationwallandthedewpointoftheinteriorairareshowninFigure14.ThisshowsonlyacoupleshortinstancesofpredictedcondensationinearlyJanuary,andonlyontheabovegradeportionofthenorthwall.


Thisanalysisfortheun‐insulatedbasementassumesthattheinteriorrelativehumidityiscontrolledto31%inthewinterand58%inthesummer(Figure12).ThiswouldlikelyrequireadehumidifiersincetherearenovaporcontrollayersonthefoundationwallorbasementslabandthemoistureloadfromthesesurfaceswouldkeeptheRHinthebasementspacehigh.Iftherelativehumidityiscontrolledtothetheserelativehumiditiesasaminimumcontrol,thenthisbasementwillperformreasonablyfromamoistureperspective,withlittleriskofmould.Fromathermalcontrolperspective,however,thiswallisaverypoorperformer.

Figure 14 : Condensation Potential for Interior air on the Surface of the Concrete Foundation Wall

2.2.5. Case 3 - Code compliant basement Cases2and3weresimilarenoughthatseparatesimulationsforbothconditionswerenotrequired.Thesesimulationswereconductedwithapolyethylenevaporbarrierbecausetherearemanybasementsinexistencebuiltwithapolyethylenevaporbarrierontheinteriorsurfaceofthewall.TheIRCstatesinR601.3.1,thataClassIorIIvaporretarderisnotrequiredonbasementwallsorthebelowgradeportionofanywall.InothergeographicareassuchaspartsofCanada,thebuildingcodewithrespecttobasementshasnotbeenmodifiedtoreflectthelargenumberofbuildingfailures,andthemoisturephysicsofbasements.

Manycompanieshaveaninsulationproductsimilartoatraditionalrollbattwithpoly,butwithaperforatedfacerthatallowsvaportopassbothwaysthroughtheinteriorsurface,dependingonthetimeofyearandinteriorconditions.Simulationswerenotconductedyettoaddressaperforatedfacer,butintuitively,vapordiffusionwillbehigherbothways,andairleakagecondensationwillbesignificantlygreateracrossaperforatedfacerthananonperforatedfacer.Thisisnotarecommendedinsulationstrategy.

Figure15showstherelativehumidityatthesurfaceofthefoundationwallforwallCase3.Notsurprisinglyitisquitehigh.Theconcreteisgenerallywet,bothfromcapillarywickingandbyvapordiffusionfromtheexterior.Therelativehumiditydoesdecreaseatthetopofthefoundationwallinthesummermonths,when


theconcreteiswarmedbyexteriortemperatures.Aperforatedfacermaydecreasetherelativehumidityslightly,dependingonthevaporpermeance.

Figure 15 : Predicted Relative Humidity at the Surface of the Concrete Foundation Wall for Case 3 Inthecaseofawelldetailedpolyethylenevaporbarrier,ittrapssignificantmoistureinthewallasthewetconcretedriestotheinterior,butdoesnotallowairleakagecondensation.Figure16showsthepotentialairleakagecondensationwhenthetemperatureofthefoundationwallfallsbelowthedewpointoftheinteriorair.ThereissignificantcondensationpotentialbetweenOctoberandJanuaryforthetophalfofthefoundationwall,andfromJunetoOctoberatthebottomofthefoundationwall.Thereiscondensationpotentialformostoftheyearontheconcretefoundationwallwiththeassumedconditions.Aperforatedfacerwouldallowairleakagecondensationtooccurresultinginsignificantcondensation.

Thismeansthatthewoodframingneartheconcreteissustainedatorabove90%relativehumidityallyear,whichwilleventuallycausemouldsinceitislikelythattherewillbeliquidwatercondensationinthewallsystemunderthesesustainedconditions.


Figure 16 : Interior Air Leakage Condensation Potential for Case 3 Code Minimum Wall Predictionswerealsomadefortherelativehumidityattheexteriorsurfaceofthepolyethylenevaporbarriersinceitiscommoninabasementtoseecondensationontheexteriorsurfaceofthepoly.Figure17showsthatbetweenJuneandAugust,therelativehumiditynearthetopofthewallisapproximately100%(higheronthesouththannorth)resultingfrominwardvapordrives.Aperforatedfacercoulddecreasethispotentialforincreasedrelativehumidityatthepoly.

Asmentionedpreviously,thesesimulationsdonotincludecapillarywickingforthisanalysis.Inthefuture,thismaybeincluded,sincethecapillarywickingisasignificantsourceofmoistureintheconcreteandbasementwallsystem.


Figure 17 : Predicted Relative Humidity at the Surface of the Polyethylene Vapor Barrier for Case 3

2.2.6. Case 4 - 1” XPS and 3.5” Fibreglass Batt Case3hasseriousmoisturerelatedriskscausedbybothvapordiffusionandairleakagecondensation.Onemethodofminimizingthepotentialrisksistoinstallavaporretardinglayerthatalsoprovidesinsulationagainsttheconcretefoundation.1”ofXPSisonlyslightlyvaporpermeable,andhasanR‐valueofR5.AssumingtheXPSiswellsealedtotheconcretefoundation,thecondensationplaneisnowtheinteriorXPSsurfaceandwillbewarmerthantheconcrete,whichshouldresultinlesspotentialcondensation,andlessvapordiffusionfromtheconcrete.Expandedpolystyrene(EPS)wouldalsoworkasanairbarrierbuthasahighervaporpermeance,sotherewouldbemorevapordiffusionfromtheexterior.SimulationswouldberequiredtoassessthedurabilityofsubstitutingEPSforXPS.

Figure18showsthepredictedrelativehumidityattheinteriorsurfaceoftheXPSinsulationatthebottomandatthetopofthefoundationwallonthenorthorientationwiththreedifferentvaporcontrolstrategies.Usingonlylatexpaintonthedrywall,therelativehumidityreachesapproximately100%atthetopinthewinterandatthebottominthesummer.Byusingavaporretardingpaint(approximately1perm)onthedrywall,therelativehumidityinboththewinterandsummerimproved.

Addingapolyethylenevaporbarrier,therelativehumiditieswereexpectedtoincrease.Atthetopofthewall,therelativehumidityincreasedandwassustainedforapproximatelythreemonths,butthebottomofthewallshowednoincreaseinrelativehumidity.IncreasingtheR‐valuebyusingR‐10foaminsulationreducesthemoisturerisks(SeeCase8).


Figure 18 : Predicted Relative Humidity at the Interior Surface of XPS for Case 4 TheairleakagecondensationpotentialofCase4wasmuchimprovedoverCases2and3asshowninFigure19.Thereisstillairleakagecondensationpotentialsothedrywallmustbemadeasairtightaspossible.

Figure 19 : Interior Air Leakage Condensation Potential for Case 4


Figure20showsthepredictedsurfacerelativehumiditesattheexteriorofthedrywall/polyvaporbarrierdependingonconstructionforCase4.Thetopofthewallexperiencesinwardvapordrives,sothewallwithpolyhasthehighestrelativehumidity.Thevaporbarrierpaintallowsmoredrying,andthelatexpaintedwallhasthelowestrelativehumidity.

Figure 20 : Predicted Relative Humidity at the Exterior Surface of the Gypsum Board for Case 4

2.2.1. Case 5 - 2” XPS, 2” foil face polyisocyanurate(PIC) TherewasnoreasontoconducthygrothermalsimulationsonCase5.Providedthereisnowayforairtobypasstheboardfoaminsulationinstalledagainsttheconcretefoundation,therearenomoisturerelatedrisks.TheInsulationisanairbarrierandvaporretarding,andisnotmoisturesensitive.

2.2.2. Case 6 - 3.5” 2.0 pcf closed cell (cc) spray foam Therewerenoexpectedmoisturerelatedissueswith3.5”ofclosedcellsprayfoamsincetheinsulationiscompletelyairimpermeableandhighlyvaporretarding.Therelativehumiditybetweentheconcreteandsprayfoamismaintainedatapproximately100%butneithermaterialismoisturesensitive.Asimulationwasconductedtoshowtherelativehumidityattheinterfacebetweenthesprayfoamandtheconcretefoundationwall(Figure21).Therearenomoisturerelatedconcernswiththiswallconstructionstrategy.

Closedcellsprayfoamisausefulmethodforretrofittingbasementsthathavemoistureand/orenergyrelatedissues,sinceitcanactasavaporbarrier,airbarrier,andcapillarybreak.


Figure 21 : Predicted Relative Humidity in the Interior Surface of the Foundation Wall of Closed Cell Spray Foam Case 6


Figure 22 : Predicted Relative Humidity at the Interior Surface of Closed Cell Spray Foam Case 6

2.2.3. Case 7 - 6” 0.5 pcf open cell (oc) spray foam SimilartoCase6,opencellsprayfoamcanbesprayeddirectlyagainsttheconcretefoundationwallasaninsulationstrategytoformanexcellentairbarriersystem.However,0.5pcfopencellfoamisvaporpermeable,somoisturerelatedissuescouldoccurunderspecificconditions.Usingsixinchesoffoamwillhelpretardthevapor,andasimulationwasconductedintheinterfaceofthefoamandfoundationwallafterthesystemreachesequilibrium(Figure23).Becauseneitherconcretenorthesprayfoamissusceptibletomoisture,therearenomoisturerelatedrisksforthissystem,providedtheinteriorsurfaceisvaporpermeable.


Figure 23 : Predicted Relative Humidity at the Interior Surface of the Foundation Wall of Open Cell Spray Foam Case 7

Figure 24 : Predicted Relative Humidity at the Interior Surface of Spray Foam of Open Cell Spray Foam Case 7


2.2.4. Case 8 - 2” XPS and 3.5” fibreglass batt Case8isagoodpracticalbasementwallsystem.Figure25showsshortperiodsofelevatedRHattheinteriorsurfaceoftheXPSontheabovegradeportion(inthewinter),andatthebottomofthewall(inthesummer).BoththefiberglassbattinsulationandtheXPSareverymoisturetolerant,andthereislittleriskofcondensationunderthesesimulatedconditions.

Figure 25 : Predicted Relative Humidity at the interior Surface of the XPS for Case 8 Figure26showssomeperiodsduringtheyearwherethereisariskofairleakagecondensationofinteriorbasementaironthesurfaceoftheXPSinsulation.ItisimportanttoensuretheXPSiswelladheredandsealedtothefoundationwallsothereisnoairleakagearoundtheXPS.Theriskofcondensationonlyoccursontheabovegradeportionofthewall,andisworseonthenorthorientationthanthesouthorientationwheretherearesomesolargains.

TherelativehumiditybetweenthedrywallandfiberglassbattinsulationisshowninFigure27,andtherearenorisksofanymoisturerelateddurabilityissues.


Figure 26 : Interior Air Leakage Condensation Potential for Case 8

Figure 27 : Predicted Relative Humidity at the Exterior Surface of Gypsum Board for Case 8


2.2.5. Case 9 - 2” PIC and 3.5” cellulose SimulationswerenotconductedonCase9becauseofthesimilaritytoCase8andCase14.ThePICinCase9hasagreaterinsulationvalueanddecreasedvaportransmission,solessmoisturewillentertheframedwallfromtheconcretefoundationthaninbothCase8andCase14.

2.2.6. Case 10 – 6” 0.5 pcf open cell foam with 2x4 framing offset 2” from foundation NosimulationswereconductedonCase10becauseitwillperformthesamefromamoistureperspectiveascase7asitalsohas6”of0.5pcfopencellfoam.InCase10,theinwardmovingmoisturemayincreasethewoodmoisturecontentoftheframing.Analysisshowedthatatthebottomofthebasementwalltheexterioroftheframingwillreachapredicted85%anddryto55%RH.AtallothermonitoringlocationsthepredictedRHdidnotexceed80%.Thisshouldbeanalyzedfurther,beforebeingconstructed,asitisacomplicatedthreedimensionalhygrothermalprocesswithwoodframingandsprayfoam.Thewoodismorethermallyconductivethanthefoam,sotheexteriorsurfaceofthestudwillbewarmerthanthefoamatthesamedepth.ThiswilllikelydecreasetheRH,butcould,insomecases,increasetheexteriortemperatureoftheframingtomoreidealconditionsformoldgrowth.

2.2.7. Case 11 - 4” XPS on the exterior TherearenomoisturerelatedissueswithCase11ifacapillarybreakisusedatthebottomofthefoundationwall.TheXPSontheexterioractsasavaporcontrollayer,andcapillarybreak,sothefoundationwillstaywarm,anddrier(followingdryingofconstructionmoisture).Thelargestsourceofmoisturewillbecapillarywickingthroughthefootingandbottomoffoundationwallifitisnotaddressed.

2.2.8. Case 12 - 4” XPS in the center of foundation wall Adding4”ofXPStothecenterofthefoundationwallactsasbothacapillarybreakandvaporcontrollayerresultinginlessmoistureontheinteriorandwarmersurfacetemperatures.Thereisnoneedtosimulatethisassemblyandlittlechanceofmoisturerelatedissues.Thelargestsourceofmoisturewillbecapillarywickingthroughthefootingandbottomoffoundationwallifthatisnotaddressed.

2.2.9. Case 13 – ICF, 2” EPS on interior and exterior InsulatedConcreteFormfoundationsareaverydurableandreliableconstructionstrategy.Thetotalof4”ofEPSwillperformasbothacapillarybreakandvaporcontrollayerresultinginlessmoistureontheinteriorandwarmersurfacetemperatures.Theconcreteinthiswallsystemwilltakeaverylongtimetodrycompletelysinceitispouredbetweentwovaporcontrollayers.ThiswillnotaffectmoisturerelateddurabilityissuesprovidedthereisnoClassIorIIvaporretarderinstalledontheinterior.

2.2.10. Case 14 - 2” XPS 5.5” Fibreglass Batt Case14isthesecondhighestR‐valueassemblyinthisstudyataninstalledinsulationR‐valueofR29with2”ofXPSatR10andanR19fibreglassbatt.Thiswallwassimulatedwithbothlatexpaintandvaporbarrierpaint,sincesimulationswithCase4,asimilarwallconstructionshowedthatapolyethylenevaporbarrierincreasedmoisturerelateddurabilityrisks.ThiswallissimilartoCase8,butwithahigherR‐valueofairandvaporpermeablefiberglassbattontheinterioroftheXPS.Thiswallperformssimilarly,butwithslightlyhighermoisturerelatedriskssincethecondensationplanetemperatureiskeptloweratthetopofthewallinthewinter,andatthebottomofthewallinthesummer.


Figure28showsthatthereareelevatedrelativehumiditiesatthesurfaceoftheXPScausedbyvapordiffusionforashortperiodduringthewintermonthsattheabovegradeportionofthewall.Thisriskisdecreasedslightlywithavaporbarrierpaintonthegypsumboard.

Inthesummermonths,therelativehumidityiselevatedatthebottomofthewalliflatexpaintisusedasvaporcontrolbutdecreasedifavaporbarrierpaintisused.

Figure 28 : Predicted Relative Humidity at the interior Surface of the XPS for Case 14 ThereispotentialforsomeairleakagecondensationintheabovegradeportionofthiswallsystemalthoughsignificantlylessthanCase4.Cases8and9withlessairpermeableinsulationtotheinterioroftheXPSwillhaveevenlesspotentialsincethecondensationplanewillbewarmer.Airtightdrywalldetailscanbeusedtominimizethepotentialforairleakagecondensation.


Figure 29 : Interior Air Leakage Condensation Potential for Case 14 Wall

TherelativehumiditywaspredictedattheexteriorsurfaceofthegypsumwallboardinFigure30,whichshowsthereisnomoisturerelatedissuesattheinteriorofthewallsystem.Asshownpreviously,apolyethylenevaporbarrierwouldincreasetherelativehumidityinthesystem,andsignificantlydecreasedryingofthewallsystem.



2.2.11. Case 15 - 4” Foil-faced Polyisocyanurate 5.5” Fibreglass Batt Case15isthehighestR‐valueassemblyinthisstudyataninstalledinsulationR‐valueofR45with4”ofpolyisocyanurate(PIC)atR26andanR19fibreglassbatt.ThiswallissimilartoCase14,butwithahigherR‐valueofrigidfoamboardbetweenthefoundationwallandwoodframing.Thiswallperformssimilarly,butwithdecreasedmoisturerelatedriskssincethecondensationplanetemperatureiskeptwarmerbythehigherR‐valuePIC.

Figure31showsthereareelevatedrelativehumidites(~90%)butnoriskofcondensationonthesurfaceofthePICthroughouttheyearatanyheightonthewall.


Figure 31 : Predicted Relative Humidity at the interior Surface of the PIC for Case 15 Thereispracticallynopotentialforairleakagecondensationintheabovegradeportionofthiswallsystem(Figure32),andsignificantlylessthanCases8and14.Airtightdrywalldetailscanbeusedtominimizethepotentialforairleakagecondensation.


Figure 32 : Interior Air Leakage Condensation Potential for Case 15 TherelativehumiditywaspredictedattheexteriorsurfaceofthegypsumwallboardinFigure33,whichshowsthereisnomoisturerelatedissuesattheinteriorofthewallsystem.Asshownpreviously,apolyethylenevaporbarrierwouldincreasetherelativehumidityinthesystem,andsignificantlydecreasedryingofthewallsystem.



2.3 Enclosure Durability

Durabilityofthebuildingenclosuresystemwasalsousedtoclassifythedifferentwallconstructionscenarios.Durabilityisusedinthisreporttogrouptogethermultipledurabilityrelatedcriteriasuchasdryingofwaterleakageevents,airleakagecondensation,builtinmoisture,andsusceptibilityofdifferentbuildingmaterialstomoisturerelatedissues.Thedurabilityassessmentwillbedeterminedfromhygrothermalmodeling,aswellasqualitativelybasedontheknowledgeandexperienceofbuildingmaterialcharacteristicssuchasvaporpermeability,hygricbufferingcapacity,andsusceptibilitytomoisturerelateddamage.

2.4 Buildability

Buildabilityisakeycomparisoncriterionforpracticalpurposes.Often,thegeneralcontractorandtradeswillinfluencedesigndecisionsbasedontheperceivedcomplexityofdifferentconstructiontechniquesordeviationfromtheirstandardpractice.Anyenclosuresystemanddetailingshouldbebuildableonaproductionleveltoachievethegreatestbenefiteventhoughthetradesareoftenresistanttochangesinconstructionpractices.

Thesusceptibilityoftheenclosuresystemtopoorlyconstructedwatermanagementdetailsandpoorworkmanshipisalsoconsideredinbuildability.Thesimplerasystemistoinstallcorrectly,themorepreferableitistouse.

2.5 Material Use

Materialuseisbecomingacriticaldesignissuebecauseofincreasingconcernsofdepletingresources,andincreasingcostsofmaterialsandenergy.Someconstructionstrategiesusemoreconstructionmaterials,and


theadvantagesofincreasedthermalcontrolshouldbebalancedagainstthedisadvantagesofincreasingthebuildingmaterialsandembodiedenergy.

Atthetimethisreportwaswritten,someinsulations,suchasXPSandclosedcellsprayfoams,havehigherglobalwarmingpotentialthanalternativeinsulations,meaningtheeffectonglobalwarmingcanbetwoordersofmagnitudegreaterthanotherinsulationstrategies.ThesesignificantglobalwarmingpotentialsarecausedbytheuseofchemicalsusedintheproductionoftheinsulationsuchasHFC‐142b,HFC‐134a,andHFC‐245fa.Thesechemicalhavebetween1000and2000timesmoreglobalwarmingpotentialthanCarbondioxidemeaningthatonekgofHCFC‐142bis2000timesworseforglobalwarmingthan1kgofCO2.

Researchisbeingdonetoreducetheglobalwarmingpotentialinmanycases,andchangesarebeingmadeintheindustry,sospecificinsulationsshouldbereviewedonacasebycasebasisbeforebeingusedtodeterminetheirglobalwarmingpotential.

Embodiedenergyisthetotalenergyrequiredtogetaspecificproducttotheconstructionsiteincludingallenergytoobtaintherawmaterials,processingenergyandtransportationenergy.Insomecases,materialsthathavelessembodiedenergy,orrecycledmaterial,suchascelluloseinsulationcouldbeusedinsteadofthemoreenergyintensiveinsulations.Materialsthatareproducedlocallyrequirelessshippinganddecreasetheembodiedenergyrequired.

2.6 Cost

Thefactorwhichgenerallyhasthegreatestinfluenceonimplementationofabuildingenclosurestrategy,particularlyforproductionbuilders,iscost.Becausethecostofsomematerialsvariessignificantlydependingonlocationandcase‐specificrelationshipsbetweenbuildersandsuppliers,thecostofabuildingenclosuresystemwillbeperceivedrelativetoothersystems.Whendecidingwhichrecommendedsystemtouse,somecostestimatesshouldbedeterminedforyourlocale.

2.7 Other Considerations

Thereareoftenfactors,suchasoccupancycomfortandhealththatdonotquitefitintheothercategories,butareratheracombinationoftheothercomparisoncriteria.Onehealthrelatedcriteria,generallyassociatedwithbasementsisradongas.Radonprotectionisnotdealtwithinthisreport,butduringconstruction,itisveryeasytoinstallcomponentsthatwillmakeradonprotectionsimpleinthefutureshouldradonbeanissue.Infact,somerecommendedmeasurestakentoincreasethethermalresistanceofabasementassemblycanbedetailedtobepartofapassiveradonsystem.Forexample,thesubslabgravelbed,whichhasbeenidentifiedasacapillarybreakinthisreport,alsoservesthepurposeofcollectingsoilgasifaventstackisalsoinstalledduringconstruction.Also,detailingairbarriersysteminacontinuousmannerthroughthefoundationassembliesincreasesthethermalperformanceandblockssoilgasinfiltration.

Insomegeographicareas,somelevelsofradonprotectionwillberequiredinnewconstructionunderthebuildingcodeinthenearfuture.MoreinformationaboutradonandsoilgasresistantconstructioncanbefoundontheUSEPA’swebsite(http://www.epa.gov/radon/).


C.Results 1. CASE 1 : UNINSULATED FOUNDATION WALLS AND SLAB

TheuninsulatedbasementcasewasincludedinthisanalysisbecausethereareuninsulatedbasementsinexistenceeventhoughthecoderequirementsinDOEclimatezones4andhigherdonotallowanuninsulatedbasementinnewconstructionwherethebasementisconditioned.Theuninsulatedbasementwasincludedasabaselineforcomparisonpurposes.

Figure 34 : Uninsulated Basement

1.1 Thermal Control

Thereisnothermalcontrolinthefoundationwallsorslab.Thisresultsinhighenergylossesformostoftheyear.Significantwholehouseenergysavingscanbeexperiencedifthebasementisinsulatedbutcareshouldbetakentodesignthethermalcontrolappropriatelytotheconstructiontypetodecreasetheriskofmoisturerelatedissuesfollowinganenergyretrofit.Predictedannualheatingenergylossbasedontheselectedsimulationcriteriais57MBtus.

1.2 Moisture Control

Sincethereisnoinsulation,thereislikelynomoisturecontrolinthebasement.Watervaporfromtheexteriorisaconstantmoisturesource,andcapillarywickingthroughthefootingand/orfoundationwallmayalsobeasignificantmoisturesourceincreasingtheriskofmoisturerelatedissues.


WUFIanalysisoftheuninsulatedbasementintheHygrothermalanalysissectionshowednosignificantmoisturerelatedissues(Figure13andFigure14),iftherelativehumidityiscontrolledwithadehumidifier,althoughthebasementwilllikelystillsmelldampandmusty.

1.3 Constructability and Cost

Thereisnoconstructioncosttoleavingthebasementuninsulated,buttherearesignificantlyhigherenergycosts.


Itisnotrecommendedtoleavethebasementuninsulatedfromanenergy,comfort,andhealthperspective.Therearemanydifferentretrofitstrategiesthatcouldbeused,someofwhichareincludedinthisanalysis.


2. CASE 2 : CODE MINIMUM R10 CONTINUOUS INSULATION

AccordingtotheIECC,newresidentialconstructionofconditionedbasementsinDOEclimatezones4andgreatermustbeconstructedwithcontinuousR10insulationorR13inaframedwall.ContinuousR‐10istypicallyinstalledbyapplyingarollbattdirectlytothefoundationwallwhichconsistoffiberglassbatt.Insomeareas,therollbattiscoveredwithapolyethylenevaporbarrier,aswassimulatedinthehygrothermalanalysis.IntheIRC,therehavebeenimprovementstothebuildingcodewhichdonotrecommendaClassIorIIvaporcontrollayersinthebasementoronthebelowgradeportionofanywall.Commonlyaperforatedfacerisusedwhichisvaporandairpermeable.

Figure 35 : Typical Basement Insulation Strategy

2.1 Thermal Control

TheinstallationofR10continuousinsulation,evenasarollbatt,hassignificantenergyimprovementsoveruninuslatedfoundations,withsavingsofapproximately31MBtus(morethanhalfofanuninsulatedbasement)accordingtosimulations.Rollbattisusedbecauseitisveryinexpensiveandmeetscode,althoughthereareotheralternativesthatpeformbetter,asshowninsomeofthefollowingcases.Thesealternativesaremoreexpensiveforthecontractor,andhomeownersareunawareofthebenefits.


Therearemoistureissueswiththisinsulationstrategythatareevidentbothinfieldinvestigationsandsimulations.Fiberglassbattisairandvaporpermeable,somoistureandaircanmovethroughtheinsulation.


AscanbeseeninFigure15,therelativehumidityagainsttheconcretefoundationwalliselevatedthroughtheentireyear.Ifthereisairleakage(orthefacerisairpermeable)thereiscondensationpotentialontheconcretefoundationthroughmostoftheyearasshowninFigure16.Becausethesesimulationsareonedimensional,theyaregoodapproximations,butheatflowinthefoundationwallisthreedimensional.Also,intheairpermeableinsulation,convectiveloopingislikely,whichmayincreasethecondensationabovepredictedresults.Fieldinvestigationsshowthatitisquitecommontogethighquantitiesofmouldinthiswallsystem


Thisisthemostinexpensivealternativeintermsofinitialcapitalcost,whichisthereasonitischosen.Continuousrollbattmakesfinishingthebasementwithgypsumboarddifficult,unlesstherollbattisremoved.


Thiswallisnotrecommendedbasedonthisanalysis,otherreports,andfieldinvestigationsofmouldybasements.


3. CASE 3 : R13 FIBERGLASS BATT IN A 2X4 FRAMED WALL

Case3isasecondalternativetotheminimumcoderequiredbasementinsulationinDOEclimatezones4andhigher.Thisconstructionusesa2x4framedwallagainsttheconcretefoundationwithR13battsinthestudspace.Thehygrothermalsimulationandapolyethylenevaporbarrierontheinterior.

Figure 36 : Case 3 - 2x4 framed wall with fiberglass batt

3.1 Thermal Control

ThisconstructiontechniqueperformsverysimilarlytoCase2.Theparallelpathmethod,takingintoaccountthehigherconductivityoftheframingmembersat24”oncenterresultsinaR‐valueinsidetheconcretewallofR12.6.Thisresultsinatotalannualpredictedheatingenergyloss23.9MBtus,asavingsof32.8MBtus.


ThisinsulationstrategyhasaverysimilarpoormoisturecontrolleveltoCase2.Moistureisconstantlymovingfromthebelowgradeexteriorportionofthefoundationwalltotheinterior,andbecomingtrappedintheframedwallcavity.Therelativehumidityiselevatedandcondensationisalmostguaranteedbothontheconcretewallandonthepolyethylenevaporbarrierthroughouttheyear(Figure15).Ifthereisairleakage(orthefacerisairpermeable)thereiscondensationpotentialontheconcretefoundationthroughmostoftheyearasshowninFigure16.Becausethesesimulationsareonedimensional,theyaregoodapproximations,butheatflowinthefoundationwallisthreedimensional.Also,intheairpermeableinsulation,convective


loopingislikely,whichmayincreasethecondensationabovepredictedresults.Fieldinvestigationsshowthatitisquitecommontogethighquantitiesofmouldinthiswallsystem


ThiswallisslightlymoreexpensivethanCase2becauseoftheframinglumberrequiredbutdoeshavetheaddedbenefitofbeingabletofinishiteasierbyaddingservicesanddrywalleasier.


Thiswallconstructiontechniqueisnotrecommended,becauseoftheobviousmoisturerelateddurabilityissuesobservedinthefield,andshownbysimulations.Thewoodframinginthiswallisatriskofmouldandrotafterprolongedexposuretotheconditionspredictedinthewallsystem.


4. CASE 4 : 1” XPS, 2X4 WOOD FRAMED WALL WITH FIBREGLASS BATT

Thisinsulationstrategyissimilartocase3butwiththeaddedinsulationvalue,andmoisturecontrol,of1”ofXPSbetweentheframedwallandconcretefoundationwall.

Figure 37 : Case 4 - 1"XPS and 2x4 framed wall with fiberglass batt

4.1 Thermal Control

ThiswallhasaparallelpathcalculationmethodofR18becausethethermalbridgingoftheframedwallisminimized,theoverallimprovementinRvalueisR5.4foroneinchofR5insulation.Adding1”ofXPSresultsinanenergysavingsof2.2MBtuoverCase3withoutaninchofXPS,butwillalsoreduceconvectiveloopingbecausethetemperaturegradientintheframedwallisless.


Thegreatestbenefittoadding1”ofXPSisarguablyformoisturecontrolandnotthermalcontrol.XPScontrolstheflowofwatervaporfromtheconcretetotheframedwall,frombothvapordiffusionthroughtheconcreteandcapillarywickingupthewall,reducingtherelativehumidityinthewallcavity.Smallamountsofmoisture(toosmalltodrain)betweentheXPSandconcreteisirrelevantbecauseneitherconcreteorXPSissusceptibletomoistureissues.TheXPSmustbewellattachedtotheconcretefoundation,andsealed,soairisnotabletobypasstheXPSinsulation.


TheXPSinsulationalsoincreasesthetemperatureofthecondensationplane,minimizingcondensationofelevatedinteriorrelativehumidity.Figure19showsthatthereisstillpotentialformoisturecondensationbutitissignificantlylessthanCase3.

Figure18showstherelativehumiditylevelsattheinteriorsurfaceoftheXPSwhicharesignificantlylowerthanthesurfaceoftheconcreteinCase3.Therelativehumidityisshowntobeafunctionofthevaporcontrolontheinteriorsurface,withvaporbarrierpaint(approx1perm)performingbetterthanlatexpaintorapolyvaporbarrier.Evenwithjustlatexpaint,theriskofmoistureissuesisminimal,iftherelativehumidityinthebasementiscontrolled.


Theconstructabilityofthiswallsystemisnotdifficult,butcareshouldbetakenthatairisunabletogetbehindtheXPS.Thiscouldbeaccomplishedwithtape,caulking,cansofsprayfoamoracombinationofthethree.Itisnotlikelythattapewillmaintainagoodairsealforthedesiredlifetimeofthewallsystem.ThiswallperformssignificantlybetterthanCase3,atonlyasmallincreasedcost.


ThiswallconstructionisanimprovementoverCases2and3,butthereareevenbetteroptionsforthermalandmoisturecontroldiscussedinthefollowingCases.Thisisanaffordableoptionthatmanypeoplecoulddothemselves,withsignificantlylessmoisturerelatedrisksthanCases2and3,resultinginamorecomfortableandhealthyspace.


5. CASE 5 : 2” XPS, 2” FOIL FACED POLYISOCYANURATE

Whenconstructingwithplasticboardfoams,thebuildingcodesrequirethatthefoamnotbeleftexposedasafirehazard.Thermalbarriersarerequiredoverbothboardfoamsandsprayfoamsinmanycases.Thermax™fromDowisathermallyratedfoamboardinsulationthatcanbeleftexposedandcouldbeusedinthissystem.Gypsumboardcouldalsobeusedtocovertheinsulation,butinsomegeographicareas,gypsumboardcanonlybeinstalledifthebasementiselectricallywiredtomeettheelectricalcode,whichdrivesupcostsubstantially.

Figure 38 : Case 5 – 2” XPS, 2” foil faced polyisocyanurate (Recommended)

5.1 Thermal Control

ThisproposedwallsystemperformsverywellthermallyatapproximatelyR23,andincombinationwithunderslabinsulationandthermalbreakattheslabedgeasshowninFigure38,thepredictedannualheatingenergylossis15.8MBtus,animprovementof40.8MBtusoveranuninsulatedwallforthecasestudyhouse.


Providedthataircannotbypasstheinsulationlayers,thisstrategywillnotexperienceanymoisturerelatedissuesfromvapordiffusion,orcapillarywicking.Capillarywickingislimitedbythethermal/capillarybreakattheedgeoftheslab,andspecifiedontopofthefooting.



Theseamsinthetwolayersoffoaminsulationshouldbeoffsetandwellsealed.Athermalbarrierisrequiredbycodeinmostjurisdictions.Thermax™byDowisafoilfacedpolyisocyanurateinsulationthatiscodecompliant.

Tofinishthebasement,drywallwouldbeadded,whichobviatestheneedforfirecontrolinthefoam.


Astudwallwillstillneedtobeconstructedtofinishthisbasementwithservicesanddrywall,soifthelongtermplanistofinishbasement,thisproposedwallsystemmaynotbethemosteconomicalchoice.

Insteadofusingtwodifferentboardfoaminsulations,itcouldbeconstructedwithtwolayersofPIC,ortwolayersofXPSwithdrywallinteriorfinish.

Thisbasementinsulationstrategyisrecommendedasadurable,comfortable,andhealthybasementsystem.


6. CASE 6 : 3.5” 2.0 PCF CLOSED CELL SPRAY POLYURETHANE FOAM

AsshowninFigure39,thesprayfoamcanbeapplieddirectlytotheconcrete,butaspreviouslymentioned(andspecifiedinthedesigndetails),ifthefoamisleftexposeditwillrequireathermalbarrier,typicallyaspray‐onthermalbarrier.Theotheroptionistobuildastudwallinfrontofthesprayfoamandusegypsumwallboardasthethermalbarrier.

Figure 39 : Case 6 – Closed Cell spray foam

6.1 Thermal Control

Closedcellsprayfoamprovidesverygoodcontinuousthermalcontrol.Sprayfoamisanairbarrier,soconvectiveloopingandairleakagethermallossesdonotoccur.ThiswallsystemhasanR‐valueofR21andapredictedannualheatingenergylossof16.4MBtus.Morethermalcontrolcouldeasilybeaddedbysprayingmorefoamagainstthewall.


Becauseclosedcellsprayfoamisanairandvaporbarrier,therearenoriskstoairleakageorvapordiffusioncondensation.Theconcreteisunabletodrytotheinteriorthroughclosedcellsprayfoam,butconcreteisgenerallynotaffectedbyahighmoisturecontent.Figure21showstherelativehumidityinthemiddleofthefoamdoesnotexceed80%,whichmeanstherearenomoisturerelatedrisksfromvapordiffusion.



Inthisproposedwallsystem,itispossibletoembedtheframingmembersinthefoam(similartoCase10,toincreasetheinteriorspace.Theframingshouldnotbeincontactwiththefoundationwalltolimitthermalbridging,andpotentialmoisturerelatedissueswiththeframingmembers.Closedcellsprayfoamcanbemoreexpensivethanotheroptions,butreduceslabourtimeoversomeoftheotherwalls,andisappliedbyaskilledlabourersothesystemisverydurableasalongtermsolution.

Sprayonthermalbarrierscanaddsignificantcosttothesprayfoaminstallation,butareregionspecific.

Closedcellsprayfoaminstalledontheinterioroftheconcretefoundationwallistheeasiestandsafestwaytoretrofitanexistingbasement.Sprayfoamcanbeinstalledincombinationwithadrainagemattandinteriordrainagetileinbasementsthathaveliquidwateringressissues.


Sprayfoamshavebeenimprovedconsiderablyforhumanhealthandtheenvironment.Ozonedepletingsubstancesintheprocesshavebeenremoved,butsomesprayfoamsusegreenhousegasesthataremuchworsethancarbondioxide.Thereareoptionsavailableofmoreenvironmentallyfriendlysprayfoamsthatdonotreleasegreenhousegases,suchaswaterblownfoams,onthemarketandshouldbeconsidered.


7. CASE 7 : 6” 0.5 PCF OPEN CELL SPRAY FOAM

AsshowninFigure40,opencellsprayfoamcanbeapplieddirectlytotheconcrete,butaspreviouslymentioned(andspecifiedinthedesigndetails),ifthefoamisleftexposeditwillrequireathermalbarrier,typicallyaspray‐onthermalbarrier,orthebasementcanbefinishedwithdrywall.

Figure40showsXPSorfoil‐facedpolyisocyanurateinstalledontheinterioroftherimjoistandfoundationwall.TheWUFIsimulationsforthefoundationwallwereconductedwithoutthislayerofboardfoaminMinneapolis,anditwasfoundthattherewerenomoisturerelatedissues,inpartbecausetheconcreteisnotassusceptibletomoisture.Installingboardfoamonthefoundationwallwillfurtherincreasethefactorofsafetyoverthepredictedresultsandmayberequiredincolderclimates.Therimjoistwasnotsimulatedinthisstudy,sinceitwassimulatedpreviously,butbecauseofthesusceptibilityofthewoodtomoisturerelateddurabilityissues,andthevaporpermeanceofthefoam,itisrecommendedtousetheboardfoamattherimjoisttolimitvapordiffusionandincreasethetemperatureofthepotentialcondensationsurface.

Figure 40 : Case 7 – Open Cell Spray Foam (Recommended)

7.1 Thermal Control

Opencellsprayfoamprovidesverygoodcontinuousthermalcontrol.Sprayfoamisanairbarrier,soconvectiveloopingandairleakagethermallossesdonotoccur.ThiswallsystemhasanR‐valueofR21andapredictedannualheatingenergylossof15.8MBtus.



Opencellsprayfoamisanairbarrier,butisvaporpermeable.Figure40showstheXPSinsulationdetailrequiredattheabovegradeportionofthefoundationwallforcoldclimateconstructiontominimizemoisturecondensationatthecoldconcreteinthewintermonths,andminimizeinwarddrivenvaporinthesummermonths.

Therelativehumiditywaspredictedinthecenteroftheopencellsprayfoaminsulationandwasfoundtobeatsafelevels(Figure24).

Lowpermeanceinteriorwallfinishes(<ClassIII)shouldbeavoidedwiththisconstructionstrategysothematerialcharacteristicsofthesprayonthermalbarriermustbeconsidered.


Opencellsprayfoamislessexpensivethanclosedcellsprayfoambutdoesdecreasetheinteriorusefulspaceandvaporcontrolshouldbeconsideredforthissystem.

Thisproposedwallsystemdoesnotallowforfinishingofthebasementwithoutinstallinganinteriorframedwall.Ifthelongtermgoalistofinishtheinteriorofthebasement,Case10shouldbeconsideredinstead.

Sprayonthermalbarrierscanaddsignificantcosttothesprayfoaminstallation,butareregionspecific.


Thisisarecommendedwallconstructionprovidedthatthedetailsforcoldclimatesarefollowed,includinganextralayerofvaporcondensationprotectionfortheabovegroundportionofthewall.

Sprayfoamshavebeenimprovedconsiderablyforhumanhealthandtheenvironment.Ozonedepletingsubstancesintheprocesshavebeenremoved,butsomesprayfoamsusegreenhousegasesthataremuchworsethancarbondioxide.Thereareoptionsavailableofmoreenvironmentallyfriendlysprayfoamsdonotreleasegreenhousegases,suchaswaterblownfoams,onthemarketandshouldbeconsidered.


8. CASE 8 : 2” XPS, 2X4 FRAMING WITH FIBREGLASS BATT

Figure 41 : Case 8 – 2”XPS, 2x4 framing with fiberglass batt

8.1 Thermal Control

ThiswallsystemhasaninstalledinsulationR‐valueofR23whichisonlyslightlylowerbasedontheparallelpathcalculationmethodwhichaccountsforthewallframingassuming24”oncenter.ThisbasementcombinedwithR10undertheslabandR10thermalbreakresultsinanannualpredictedheatingenergylossof15.8MBtufortheexamplehouse.


Thewatervapordiffusionandcapillarywickingarecontrolledby2”ofXPSinsulationassumingthattheXPSiswellsealedtotheconcrete.ThiswallsystemwasnothygrothermallysimulatedsinceitwillperformbetterthanCase14fromamoisturepointofview,andCase14performedwell.Case14has5.5”offiberglassbattinsulationwhichwillresultincoldercondensationplane.Case14hadsomecondensationpotentialbutimprovedperformancewithavaporretardingpaint.Therewassomepotentialforairleakagecondensationattheabovegradesectionofthewallinthewinteralternatingwithdryingperiods.


Itmaybedifficulttoget2”boardsofXPSattachedwelltothenonuniformsurfaceoftheconcretefoundationbecausetheinsulationissostiff.Itiseasierinsomecasestouse21”thickboards,thatwillflexoverimperfections.Thejointsintheinsulationshouldbeoffsetiftwolayersof1”XPSareused.



Case8isoneofthesimplestandleastexpensivemethodsofminimizingthemoistureriskandsavingenergy.Itispossibletouseotherairpermeableinsulationsinsteadoffibreglassbattincludingdampspraycellulose,orsprayfibreglass.

9. CASE 9 : 2” POLYISOCYANURATE INSULATION, 2X4 FRAMING WITH CELLULOSE

Figure 42 : Case 9 – 2” polyiso, 2x4 framing with cellulose

9.1 Thermal Control

ThiswallsystemhasaninstalledinsulationR‐valueofR25whichisonlyslightlylowerbasedontheparallelpathcalculationmethodwhichaccountsforthewallframingassuming24”oncenter.ThisbasementcombinedwithR10undertheslabandR10thermalbreakresultsinanannualpredictedheatingenergylossof15.45MBtus.


Thewatervapordiffusionandcapillarywickingarecontrolledby2”ofPICinsulationassumingthatthePICiswellsealedtotheconcrete.Thiswallsystemwasnothygrothermallysimulatedsinceitwillnotexperienceanymoisturerelatedissues.Thefoilfaceonthepolyisocyanuratewillnotallowvapordiffusionfromtheconcretefoundation,andtheincreasedR‐valueofPICcomparedtoXPSwillincreasethecondensationsurfacetemperaturecomparedtoCase8andCase14,resultingindecreasedcondensationpotential.



Fiberglassbattinsulationcouldbeusedintheplaceofcellulosetodecreasethecostoftheassembly.


Case8isoneofthesimplestmethodsofminimizingthemoistureriskandsavingenergywhichalsoallowsthebasementtobefinished.Itispossibletouseotherairpermeableinsulationsinsteadofcelluloseincludingfiberglassbattorsprayfiberglass.

10. CASE 10 : 6” 0.5 PCF SPRAY FOAM WITH 2X4 FRAMING OFFSET 2.5” FROM CONCRETE

Figure 43 : Case 10 – 6” open cell foam

10.1 Thermal Control

Opencellsprayfoamprovidesverygoodcontinuousthermalcontrol.Sprayfoamisanairbarrier,soconvectiveloopingandairleakagethermallossesdonotoccur.ThiswallsystemhasanR‐valueofR21andapredictedannualheatingenergylossof16.3MBtus.


Opencellsprayfoamisanairbarrier,butisvaporpermeable.Therelativehumiditywaspredictedinthecenteroftheopencellsprayfoaminsulationandwasfoundtobeatsafelevels(Figure24).


Lowpermeanceinteriorwallfinishesshouldbeavoidedwiththisconstructionstrategy.


ThissolutionismorepracticalthanCase7iftheplanistofinishtheinteriorofthebasement.


Sprayfoamshavebeenimprovedconsiderablyforhumanhealthandtheenvironment.Ozonedepletingsubstancesintheprocesshavebeenremoved,butsomesprayfoamsusegreenhousegasesthataremuchworsethancarbondioxide.Thereareoptionsavailableofmoreenvironmentallyfriendlysprayfoamsthatreleasegreenhousegases,suchaswaterblownfoams,onthemarketandshouldbeconsidered.

11. CASE 11 : 4” XPS INSULATION ON THE EXTERIOR OF FOUNDATION WALL

Figure 44 : Case 11 – Exterior XPS insulation


ThisproposedwallsystemhasaninstalledinsulationR‐valueofR20andresultsinheatingenergylossof19.43MBtusforthespecificchosenparameters.Theadvantageofinsulatingontheexterioristhattheinsulationontheexteriorofthefoundationcanbejoinedwiththeexteriorinsulationonthefirstfloor,whichformsacontinuouslayerofinsulationandvaporcontrol.Thethermaldisadvantageofthissystemisthatthereisathermalbridgethroughtheconcretewall,andfootingintotheground.



FourinchesofXPSisagreatvapordiffusionresisterandcapillarybreakforinwardmoisturemovement.Thereisstillcapillarywickingpotentialthroughthefootingintotheinteriorsurfaceofconcreteresultinginmoistureattheinteriorsurfaceevaporatingintotheinteriorspaceifitisnotdetailedcorrectly.Thispotentialmoistureissuecanbesolvedbyusingacapillarybreak(eitherliquidappliedorplasticbased)onthetopofthefootingasnotedinthedesigndetails.Unlikesomeoftheotherproposedfoundationwallsystems,theexposedconcreteinthissystemwillprovidemoisturebufferingcapacity,onceithasdried.


Thisproposedwallsystemwithexteriorinsulationisperceivedasdifficulttotheconstructiontrades,andthefinishingoftheabovegradeportionmaynotbearchitecturallydesirable.Insomecasesthetimingoftheinsulationinstallationtradescanbetrickysincetheentirehouseisnotinsulatedatonceinthiscase.


Insomecases,exteriorfoundationisnotallowedbythebuildingcodeduetocomplicationswithtermitesandotherinsects.Whereinsectsmaybeanissue,Case12proposedwallsystemcouldbeused.

12. CASE 12 : 4” XPS INSULATION IN THE CENTER OF FOUNDATION WALL

Figure 45 : Case 12 – Interstitial XPS Insulation



ThisconstructionstrategyhasaninstalledinsulationR‐valueofR20,andhasapredictedannualheatingenergylossof19.24MBtus.Unlikesomeoftheotherwallsystemstheremaybethermalmassbenefitsoftheinteriorexposedsurfaceofconcrete.Thereisasmallthermalbridgethroughthefootingandinteriorsurfaceofconcretethatdoesincreasetheenergyrequiredoverawallthatisinsulatedcompletelyontheinterior


FourinchesofXPSisagreatvapordiffusionresisterandcapillarybreakforinwardmoisturemovement.Thereisstillcapillarywickingpotentialthroughthefootingintotheinteriorsurfaceofconcreteresultinginmoistureattheinteriorsurfaceevaporatingintotheinteriorspaceifitisnotdetailedcorrectly.Thispotentialmoistureissuecanbesolvedbyusingacapillarybreak(eitherliquidappliedorplasticbased)onthetopofthefootingasnotedinthedesigndetails(Figure45).Unlikesomeoftheotherproposedfoundationwallsystems,theexposedconcreteinthissystemwillprovidemoisturebufferingcapacity,onceithasdried.


Thisconstructionstrategyisnotverycommon,butisverydurablebecausetheXPSissealedintotheconcreteandprotectedfrominteriorandexteriordamage.Thiswalldesignismoreexpensivethaninstalling4”ontheinteriorortheexterior.


Thisproposedwalltypemaynotbelocallyavailable.


13. CASE 13 : INSULATED CONCRETE FORMS, 2” XPS ON INTERIOR AND EXTERIOR

Figure 46 : Case 13 –Insulated Concrete Forms (ICF)


ThisconstructionstrategyhasaninstalledinsulationR‐valueofR20,andhasapredictedannualheatingenergylossof16.7MBtus.


TwoinchesofXPSontheinterior,connectedtothethermalbreakattheslabedge,controlstheinteriorvapordriveandcapillarywickingtotheinteriorsotherearenomoisturerelatedissuesfrominwardvapordiffusionorcapillarywicking.


Theinterioroftheinsulatedconcreteformwillrequiredrywallorotherthermalbarriertoachievethefireratingrequiredbycode.ThegypsumboardisveryeasytoattachtotheplasticclipsdesignedintotheICF.Thedrywallshouldnotbepainted,ifitisnotnecessary,toallowmaximumdryingoftheconcrete.Itmaybeeasierandmorepracticaltoinstallathinframedwall(eg.2x3woodorsteelframing)ontheinterioroftheICFtoallowanynecessaryservicestoberuninthewall,andpotentiallymoreinsulation.



Becausetheconcreteisinstalledbetweentwovaporretardinglayers,itwilltakeseveralyearsfortheconcretetodrytoequilibrium.Sinceadditionalinteriorvaporcontrolshouldbeavoided,nomorethanlatexpaintshouldbeusedontheinteriorsurfaceofthedrywall.

14. CASE 14 : 2” XPS, 2X6 FRAMING WITH FIBREGLASS BATT



ThisfoundationwallsystemhasacalculatedparallelpathR‐valueofR28.7,andayearlyheatingenergyconsumptionof14.79MBTusassumingR10undertheslabandinthethermalbreak.Onlyiftherestoftheenclosureissuperinsulated,andairtight,inaverycoldclimatewillitmakesensetoincreasetheR‐valueofthefoundationwall.ItmaymakesensewithanR30foundationwalltoincreasetheunderslabinsulationtoR15orR20.Thisshouldbeexaminedinmoredetail.


ThiswallwasanalyzedinWUFItopredictthemoisturerelatedriskinthewallsystem,anditwasshownthattheRHatthesurfaceoftheXPSintheabovegradeportionofthewalliselevatedinthewintermonths(Figure28),andthatthereissomecondensationpotentialalternatingwithperiodsofdryingpotentialatthetopofthefoundationwall.(Figure27).ThereislittleriskofmoisturerelatedissuesinthisallsystemiftheinteriorRHiscontrolledwithadehumidifier,andtheinteriordrywalliswellairsealed.



ThiswallsystemisslightlymoreexpensivethanCases8and9byincreasingthedepthoftheframedcavitywith2x6framinginsteadof2x4framing.Itispossibletouse2x4framingstoodoutfromtheXPSby2inches,anduseR19fiberglassbatts,orblowncelluloseorfibreglass.R19fiberglassbattsshouldbelessexpensivethanR13fiberglassbattsbecausethemanufacturingprocessforbothR19andR13battsusesthesameamountoffibreglass,buttheR13battsrequiremoretimeandefforttocompactto3.5”makingthemmoreexpensivetoproduce.


15. CASE 15 : 4” PIC, 2X6 FRAMING WITH FIBREGLASS BATT



ThisfoundationwallsystemhasacalculatedparallelpathR‐valueofR45.0,andayearlyheatingenergyconsumptionof11.09MBTusassumingR20undertheslabandinthethermalbreak..ThisisthehighestRvaluefoundationsysteminthisstudy,andislikelynotcosteffectiveunlesstherestofthehouseissuperinsulatedandairtight.


ThiswallwasanalyzedinWUFItopredictthemoisturerelatedriskinthewallsystem,anditwasshownthattheRHatthesurfaceoftheXPSintheabovegradeportionofthewallisslightlyelevatedinthewinter


months(Figure31),butdoesnotexceed90%.Thereisalmostnocondensationpotential(Figure32)exceptontheupperwallofthenorthorientationfortwoveryshortperiods.ThereisvirtuallynoriskofmoisturerelatedissuesinthisallsystemiftheinteriorRHiscontrolledwithadehumidifier,andtheinteriordrywalliswellairsealed.


ThiswallsystemisslightlymoreexpensivethanCases14bychangingthe2”ofXPSto4”offoil‐facedpolyisocyanurate.Itispossibletouse2x4framingstoodoutfromtheXPSby2inches,anduseR19fiberglassbatts,orblowncelluloseorfibreglass.R19fiberglassbattsshouldbelessexpensivethanR13fiberglassbattsbecausethemanufacturingprocessforbothR19andR13battsusesthesameamountoffibreglass,buttheR13battsrequiremoretimeandefforttocompactto3.5”makingthemmoreexpensivetoproduce.


Dependingonsitespecificconditions,andlocalcosts,thiswallislikelynoteconomicaltobuildunlessthehouseisveryhighlyinsulatedandairtight.


D.Conclusions HeatingenergylosscalculationsforalloftheassemblieswerecalculatedusingBasecalcandthesummaryisshowninTable5below.TheheatingenergylosseswereconductedforabasementinMinneapolis(DOEclimatezone6),withanareaof1614ft2.

Table 5 : Summary of Basecalc Results

Analysisshowedthatevenasmallamountofinsulationonthefoundationwalldecreasedtheheatingenergylossessignificantlycomparedtoanuninsulatedbasement,butthebenefitsofincreasinginsulationdecreaseasmoreinsulationisadded.InCases5through13,noneofthewallsperformsignificantlybetterthantheothersfromaheatingenergylossesperspective,soanydecisionsshouldbebasedoncost,durabilityanddesiredfinish.

Insulatingbelowthebasementslabandattheinterfaceofthefoundationwallandbasementslabwillresultinenergysavings,butthegreatestbenefitismoisturerelatedsincetheyformavapordiffusionandcapillarybreakbetweenthemoistureandtheinteriorenvironment,resultinginadrier,healthierinteriorenvironment.

Besidesbulkwatermovement,whichisnotspecificallyaddressedinthisreport,therearetwomodesofwettinginthefoundation;vapordiffusionandcapillarywetting.Theexteriorsurfaceofthebelowgradeportionofanyfoundationwallismaintainedatapproximately100%relativehumiditysomoisturemovementbelowgradeisalwaystotheinterioranddryingisnotpossibletotheexterior.TheIRChasbeenmodifiedtoreflectthis,notrecommendingaClassIorIIvaporcontrollayerontheinteriorofanybelowgradewall.

Capillarywickingthroughthefootingintothefoundationwallisgenerallynotaddressedbyproductionbuilders,andcanresultinsignificantamountsofmoistureevaporatingfromtheinteriorsurfaceofthebasementwall.

Cases2and3representcodeminimumbasementinsulationamounts,althoughthesewerehygrothermallysimulatedwithaninteriorpolylayerinsteadofaperforatedlayer,whichshouldbesimulatedinfuturework.Withapolyethylenevaporbarrier,thesewallsperformverypoorly,withhighrelativehumiditiesintheinsulation,andairleakagecondensationpotentialfornearlytheentireyear.Intrusiveinvestigationsofbuildingsinthefieldhaveshownthatmoisturerelatedissues(includingmould,rot,andodours)canbeexpectedwiththistypeofwallconstruction.


Cases4,8,9,and14witharigidfoamagainsttheconcretefoundationandairpermeableinsulationinawoodframedwall(fiberglassbattorcellulose)showedsignificantimprovementsinmoistureperformanceoverCase2and3.Thereisstillsomepredictedairleakagecondensationpotential,butgenerallyisolatedtotheabovegradeportionofthewall,duetotheverycoldexteriortemperatures.

Case5with2”ofXPSand2”ofpolyisocyanuratehasnomoisturerelatedissuesandperformsverywell,butdoesnoteasilyallowforinteriorfinishescomparedtosomeotherproposedfoundationinsualationsystems.

Case6,7,and10usesprayfoamapplieddirectlyagainstthefoundationwall,whichformsanairbarriersystemresultinginnoairleakagecondensation.Closedcellsprayfoamisavaporbarrierlimitingdiffusiontotheinteriorandopencellfoamismorevaporpermeable,butsimulationspredictednomoisturerelatedissuesfromvapordiffusionduetothethicknessoffoam,andtheabilityofsmallamountofvaportodrytotheinteriorthroughthefoamandinteriorfinish.Attheabovegradeportionofthewallincoldclimates,alowerpermeanceboardfoamisrecommendedtocontroltheinwardvapordriveinthesummermonths,andlimitthevapordiffusioncondensationinthewintermonths.Therearenomoisturerelatedissuespredictedforthesprayfoamwalls.

Cases11,12,and13areallconstructedwith4”ofXPSindifferentlocationsonthefoundationwall,andallresultingoodmoistureperformance.Acapillarybreakisalwaysrecommendedbetweenthefootingandthefoundationwall,andinCase11,and12,itisrequiredsincethevaporcontrollayer,thatdecreasestheevaporationandvapordiffusionfromtheinteriorsurface,isdiscontinuousontheinteriorsurface.Cases11,and12alsohaveslightlyhigherheatingenergylossesbecauseofthethermalbridgealongtheinteriorsurfaceofthefoundationwallthroughthefooting,buttheydohavetheadvantageofboththermalandmoisturebufferingiftheinterioroftheconcretewallisleftexposed.

Followingtheanalysisofallproposedfoundationwallsystems,valueswereassignedforthefivecomparisoncriteria;

• Thermalcontrol• Durability• Buildability• Cost• Materialuse

Thesewallswerescoredonascaleof1to5foreachcriterion,onebeingtheworst,andfivebeingthebestperforming,andtheresultsareshowninTable6.Basedontheselectedcriteria,thetwohighestscoringwallswereCase6with3.5”of2.0pcfclosedcellspufandCase7with6”of0.5pcfocspf.BecausesomeofthecriteriasuchasMaterialUseandCostcouldbedifferentinotherregions,thefinalresultscouldbedifferentindifferentpartsofthecontinent.

Allofthecriteriaarecurrentlyweightedevenly,buttheycouldbechangeddependingontheconcernsofthecontractororhomeowner.Usingmultipliersbetween1and5beforesummingthescorescouldresultindifferentresultsbasedontheimportanceofdifferentcriteria.


Table 6 : Comparison Criteria Matrix with Scoring Results

E. Future Work Whileconductingthisanalysis,somequestionswereencounteredthatrequirefurtherresearch,analysisandsimulationstomorecompletelyunderstandthemoistureandthermalperformanceofbasementinsulationsystems.Theseareasinclude;

• DeterminingtheeffectofperforatedfacersoncodecompliantR10rollbatts• Researchingfieldtestingdataonbasementmonitoringdatathathasbeenconductedand

correlatetotheproposedwallsystems.• FurtheranalysisoftheMitalasfiniteelementanalysismethodofheatingenergylossfor

basements.• Attempttoquantifytheroleofcapillarywickingthroughthebasementwallrelativetothe

vapordiffusionload.SomeworkhasbeenconductedalreadybyKohtaUenoofBuildingScienceCorporationaspartofaBuildingAmericaFoundationsExpertsGroupMeeting.

FollowingthecompletionoftheHigh‐Rbasementandfoundationreport,ananalysisreportwillbecompletedforroofsandatticsregardinghistorical,codecompliantandsuperinsulatedroofstrategies.Similarlytothe


previousHighRWallReportandthisBasements/Foundationsreport,theRoofandAtticreportwillbeacombinationofbothfieldtesting/monitoring,thermalandhygrothermalanalysis,yearsofexperience.

F. Works Cited Lstiburek,J.UnderstandingBasements,BuildingScienceDigest103,Westford,BuildingSciencePress,2006

Mitalas,G.P.,CalculationofBasementHeatLoss,NationalResearchCouncilCanada

Pettit,B.,RenovatingExistingBasements,ResearchReport–0509c,Westford,BuildingSciencePress,2008

Straube,J.,andBurnett,E.,BuildingScienceforBuildingEnclosures.Westford,BuildingSciencePress,2005

Straube,J.,Smegal,J.,BuildingAmericaSpecialResearchProject:HighRWallsCaseStudyAnalysis,BuildingSciencePress,MA,2009

BA-1003: Building America Special Research Report High-R Foundation Case Study Analysis

About this Report

This report was prepared with the cooperation of the U.S. Department of Energy’s, Building America Program.

About the Authors

Jonathan Smegal’s work at BSC includes laboratory research, hygro-thermal modeling, field monitoring of wall performance, and forensic analysis of building failures.

John Straube teaches in the Department of Civil Engineering and the School of Architecture at the University of Waterloo. More information about John Straube can be found at www.buildingscienceconsulting.com.

Direct all correspondence to: Building Science Corporation, 30 Forest Street, Somerville, MA 02143.

Limits of Liability and Disclaimer of Warranty:

Building Science documents are intended for professionals. The author and the publisher of this article have used their best efforts to provide accurate and authoritative information in regard to the subject matter covered. The author and publisher make no warranty of any kind, expressed or implied, with regard to the information contained in this article.

The information presented in this article must be used with care by professionals who understand the implications of what they are doing. If professional advice or other expert assistance is required, the services of a competent professional shall be sought. The author and publisher shall not be liable in the event of incidental or consequential damages in connection with, or arising from, the use of the information contained within this Building Science document.

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