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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
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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
1.4OtherConsiderations............................................................................................................................................................... 44
2.Case2:CodeminimumR10continuousinsulation........................................................................................................... 45
2.1ThermalControl......................................................................................................................................................................... 45
2.2MoistureControl........................................................................................................................................................................ 45
2.3ConstructabilityandCost....................................................................................................................................................... 46
2.4OtherConsiderations............................................................................................................................................................... 46
3.Case3:R13fiberglassbattina2x4framedwall ................................................................................................................ 47
3.1ThermalControl......................................................................................................................................................................... 47
3.2MoistureControl........................................................................................................................................................................ 47
3.3ConstructabilityandCost....................................................................................................................................................... 48
3.4OtherConsiderations............................................................................................................................................................... 48
4.Case4:1”XPS,2x4woodframedwallwithfibreglassbatt ........................................................................................... 49
4.1ThermalControl......................................................................................................................................................................... 49
4.2MoistureControl........................................................................................................................................................................ 49
4.3ConstructabilityandCost....................................................................................................................................................... 50
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4.4OtherConsiderations............................................................................................................................................................... 50
5.Case5:2”XPS,2”foilfacedpolyisocyanurate ..................................................................................................................... 51
5.1ThermalControl......................................................................................................................................................................... 51
5.2MoistureControl........................................................................................................................................................................ 51
5.3ConstructabilityandCost....................................................................................................................................................... 52
5.4OtherConsiderations............................................................................................................................................................... 52
6.Case6:3.5”2.0pcfclosedcellspraypolyurethanefoam ............................................................................................... 53
6.1ThermalControl......................................................................................................................................................................... 53
6.2MoistureControl........................................................................................................................................................................ 53
6.3ConstructabilityandCost....................................................................................................................................................... 54
6.4OtherConsiderations............................................................................................................................................................... 54
7.Case7:6”0.5pcfopencellsprayfoam................................................................................................................................... 55
7.1ThermalControl......................................................................................................................................................................... 55
7.2MoistureControl........................................................................................................................................................................ 56
7.3ConstructabilityandCost....................................................................................................................................................... 56
7.4OtherConsiderations............................................................................................................................................................... 56
8.Case8:2”XPS,2x4framingwithfibreglassbatt ................................................................................................................ 57
8.1ThermalControl......................................................................................................................................................................... 57
8.2MoistureControl........................................................................................................................................................................ 57
8.3ConstructabilityandCost....................................................................................................................................................... 57
8.4OtherConsiderations............................................................................................................................................................... 58
9.Case9:2”Polyisocyanurateinsulation,2x4framingwithcellulose.......................................................................... 58
9.1ThermalControl......................................................................................................................................................................... 58
9.2MoistureControl........................................................................................................................................................................ 58
9.3ConstructabilityandCost....................................................................................................................................................... 59
9.4OtherConsiderations............................................................................................................................................................... 59
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
11.2MoistureControl ..................................................................................................................................................................... 61
11.3ConstructabilityandCost .................................................................................................................................................... 61
11.4OtherConsiderations ............................................................................................................................................................ 61
12.Case12:4”XPSinsulationinthecenteroffoundationwall ....................................................................................... 61
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12.1ThermalControl ...................................................................................................................................................................... 62
12.2MoistureControl ..................................................................................................................................................................... 62
12.3ConstructabilityandCost .................................................................................................................................................... 62
12.4OtherConsiderations ............................................................................................................................................................ 62
13.Case13:InsulatedConcreteForms,2”XPSoninteriorandexterior ..................................................................... 63
13.1ThermalControl ...................................................................................................................................................................... 63
13.2MoistureControl ..................................................................................................................................................................... 63
13.3ConstructabilityandCost .................................................................................................................................................... 63
13.4OtherConsiderations ............................................................................................................................................................ 64
14.Case14:2”XPS,2x6framingwithfibreglassbatt ........................................................................................................... 64
14.1ThermalControl ...................................................................................................................................................................... 64
14.2MoistureControl ..................................................................................................................................................................... 64
14.3ConstructabilityandCost .................................................................................................................................................... 65
14.4OtherConsiderations ............................................................................................................................................................ 65
15.Case15:4”PIC,2x6framingwithfibreglassbatt............................................................................................................ 65
15.1ThermalControl ...................................................................................................................................................................... 65
15.2MoistureControl ..................................................................................................................................................................... 65
15.3ConstructabilityandCost .................................................................................................................................................... 66
15.4OtherConsiderations ............................................................................................................................................................ 66
D. Conclusions.......................................................................................................................................................................................... 67
E. FutureWork........................................................................................................................................................................................ 69
F. WorksCited ......................................................................................................................................................................................... 70
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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.
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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.
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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.
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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:
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• 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
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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
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Figure 4 : Comparison of Different Underslab Insulation Techniques with R10 on foundation walls
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Figure 5 : Energy Savings From Thermal Break Insulation Between Concrete Footing and Slab
2.1.2. Case Study – Westford Prototype House
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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
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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
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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.
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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).
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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
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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
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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.
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Sincethefoundationwallbelowgradeisunabletodrytotheexteriorandtherecanbeasignificantamountofmoisturepresentintheconcrete,intuitively,thevapordrivesshouldbeallowedtodrytotheinteriorandapolyethylenevaporbarriershouldnotbebuiltintotheinteriorofthewoodframedwall.Unfortunately,buildingcodeshaveoftenspecifiedpolyethylenevaporbarriersontheinteriorofframedwallsinfinishedbasementsandthesewallswillbeanalyzedtounderstandwhytheyoftenhaveseriousmoisturerelatedproblems.
Thehygrothermalsimulationsconductedforthisstudyareaonedimensionalapproximationofthehygrothermalbehaviourofeachwallsystem.Inrealitytherearetwoandthreedimensionalinteractionssuchasheattransferupanddowntheconcretefoundationwallaswellasconvectiveloopingandmoisturetransportthroughairandvaporpermeableinsulations.
BoundaryConditions
TheWUFIsimulationswereconductedinthreepartsbecauseofthedifferenthygrothermalregimesatthetopabovegradeportion,middleandbottombelowgradeportionsofthewall.TheexteriorbelowgradetemperaturesusedforhygrothermalsimulationswerebasedonmonitoringofgroundtemperaturesinSt.PaulMNasshowninFigure11.TheabovegradetemperaturesforMinneapolisareincludedintheweatherdataforWUFI.
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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.
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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
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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.
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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
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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.
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Figure 16 : Interior Air Leakage Condensation Potential for Case 3 Code Minimum Wall Predictionswerealsomadefortherelativehumidityattheexteriorsurfaceofthepolyethylenevaporbarriersinceitiscommoninabasementtoseecondensationontheexteriorsurfaceofthepoly.Figure17showsthatbetweenJuneandAugust,therelativehumiditynearthetopofthewallisapproximately100%(higheronthesouththannorth)resultingfrominwardvapordrives.Aperforatedfacercoulddecreasethispotentialforincreasedrelativehumidityatthepoly.
Asmentionedpreviously,thesesimulationsdonotincludecapillarywickingforthisanalysis.Inthefuture,thismaybeincluded,sincethecapillarywickingisasignificantsourceofmoistureintheconcreteandbasementwallsystem.
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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).
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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
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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.
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Figure 21 : Predicted Relative Humidity in the Interior Surface of the Foundation Wall of Closed Cell Spray Foam Case 6
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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.
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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
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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.
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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
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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.
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Figure28showsthatthereareelevatedrelativehumiditiesatthesurfaceoftheXPScausedbyvapordiffusionforashortperiodduringthewintermonthsattheabovegradeportionofthewall.Thisriskisdecreasedslightlywithavaporbarrierpaintonthegypsumboard.
Inthesummermonths,therelativehumidityiselevatedatthebottomofthewalliflatexpaintisusedasvaporcontrolbutdecreasedifavaporbarrierpaintisused.
Figure 28 : Predicted Relative Humidity at the interior Surface of the XPS for Case 14 ThereispotentialforsomeairleakagecondensationintheabovegradeportionofthiswallsystemalthoughsignificantlylessthanCase4.Cases8and9withlessairpermeableinsulationtotheinterioroftheXPSwillhaveevenlesspotentialsincethecondensationplanewillbewarmer.Airtightdrywalldetailscanbeusedtominimizethepotentialforairleakagecondensation.
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Figure 29 : Interior Air Leakage Condensation Potential for Case 14 Wall
TherelativehumiditywaspredictedattheexteriorsurfaceofthegypsumwallboardinFigure30,whichshowsthereisnomoisturerelatedissuesattheinteriorofthewallsystem.Asshownpreviously,apolyethylenevaporbarrierwouldincreasetherelativehumidityinthesystem,andsignificantlydecreasedryingofthewallsystem.
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Figure 30 : Predicted Relative Humidity at the Exterior Surface of Gypsum Board for Case 14
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.
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Figure 31 : Predicted Relative Humidity at the interior Surface of the PIC for Case 15 Thereispracticallynopotentialforairleakagecondensationintheabovegradeportionofthiswallsystem(Figure32),andsignificantlylessthanCases8and14.Airtightdrywalldetailscanbeusedtominimizethepotentialforairleakagecondensation.
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Figure 32 : Interior Air Leakage Condensation Potential for Case 15 TherelativehumiditywaspredictedattheexteriorsurfaceofthegypsumwallboardinFigure33,whichshowsthereisnomoisturerelatedissuesattheinteriorofthewallsystem.Asshownpreviously,apolyethylenevaporbarrierwouldincreasetherelativehumidityinthesystem,andsignificantlydecreasedryingofthewallsystem.
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Figure 33 : Predicted Relative Humidity at the Exterior Surface of Gypsum Board for Case 15
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
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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/).
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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.
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WUFIanalysisoftheuninsulatedbasementintheHygrothermalanalysissectionshowednosignificantmoisturerelatedissues(Figure13andFigure14),iftherelativehumidityiscontrolledwithadehumidifier,althoughthebasementwilllikelystillsmelldampandmusty.
1.3 Constructability and Cost
Thereisnoconstructioncosttoleavingthebasementuninsulated,buttherearesignificantlyhigherenergycosts.
1.4 Other Considerations
Itisnotrecommendedtoleavethebasementuninsulatedfromanenergy,comfort,andhealthperspective.Therearemanydifferentretrofitstrategiesthatcouldbeused,someofwhichareincludedinthisanalysis.
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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.
2.2 Moisture Control
Therearemoistureissueswiththisinsulationstrategythatareevidentbothinfieldinvestigationsandsimulations.Fiberglassbattisairandvaporpermeable,somoistureandaircanmovethroughtheinsulation.
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AscanbeseeninFigure15,therelativehumidityagainsttheconcretefoundationwalliselevatedthroughtheentireyear.Ifthereisairleakage(orthefacerisairpermeable)thereiscondensationpotentialontheconcretefoundationthroughmostoftheyearasshowninFigure16.Becausethesesimulationsareonedimensional,theyaregoodapproximations,butheatflowinthefoundationwallisthreedimensional.Also,intheairpermeableinsulation,convectiveloopingislikely,whichmayincreasethecondensationabovepredictedresults.Fieldinvestigationsshowthatitisquitecommontogethighquantitiesofmouldinthiswallsystem
2.3 Constructability and Cost
Thisisthemostinexpensivealternativeintermsofinitialcapitalcost,whichisthereasonitischosen.Continuousrollbattmakesfinishingthebasementwithgypsumboarddifficult,unlesstherollbattisremoved.
2.4 Other Considerations
Thiswallisnotrecommendedbasedonthisanalysis,otherreports,andfieldinvestigationsofmouldybasements.
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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.
3.2 Moisture Control
ThisinsulationstrategyhasaverysimilarpoormoisturecontrolleveltoCase2.Moistureisconstantlymovingfromthebelowgradeexteriorportionofthefoundationwalltotheinterior,andbecomingtrappedintheframedwallcavity.Therelativehumidityiselevatedandcondensationisalmostguaranteedbothontheconcretewallandonthepolyethylenevaporbarrierthroughouttheyear(Figure15).Ifthereisairleakage(orthefacerisairpermeable)thereiscondensationpotentialontheconcretefoundationthroughmostoftheyearasshowninFigure16.Becausethesesimulationsareonedimensional,theyaregoodapproximations,butheatflowinthefoundationwallisthreedimensional.Also,intheairpermeableinsulation,convective
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loopingislikely,whichmayincreasethecondensationabovepredictedresults.Fieldinvestigationsshowthatitisquitecommontogethighquantitiesofmouldinthiswallsystem
3.3 Constructability and Cost
ThiswallisslightlymoreexpensivethanCase2becauseoftheframinglumberrequiredbutdoeshavetheaddedbenefitofbeingabletofinishiteasierbyaddingservicesanddrywalleasier.
3.4 Other Considerations
Thiswallconstructiontechniqueisnotrecommended,becauseoftheobviousmoisturerelateddurabilityissuesobservedinthefield,andshownbysimulations.Thewoodframinginthiswallisatriskofmouldandrotafterprolongedexposuretotheconditionspredictedinthewallsystem.
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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.
4.2 Moisture Control
Thegreatestbenefittoadding1”ofXPSisarguablyformoisturecontrolandnotthermalcontrol.XPScontrolstheflowofwatervaporfromtheconcretetotheframedwall,frombothvapordiffusionthroughtheconcreteandcapillarywickingupthewall,reducingtherelativehumidityinthewallcavity.Smallamountsofmoisture(toosmalltodrain)betweentheXPSandconcreteisirrelevantbecauseneitherconcreteorXPSissusceptibletomoistureissues.TheXPSmustbewellattachedtotheconcretefoundation,andsealed,soairisnotabletobypasstheXPSinsulation.
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TheXPSinsulationalsoincreasesthetemperatureofthecondensationplane,minimizingcondensationofelevatedinteriorrelativehumidity.Figure19showsthatthereisstillpotentialformoisturecondensationbutitissignificantlylessthanCase3.
Figure18showstherelativehumiditylevelsattheinteriorsurfaceoftheXPSwhicharesignificantlylowerthanthesurfaceoftheconcreteinCase3.Therelativehumidityisshowntobeafunctionofthevaporcontrolontheinteriorsurface,withvaporbarrierpaint(approx1perm)performingbetterthanlatexpaintorapolyvaporbarrier.Evenwithjustlatexpaint,theriskofmoistureissuesisminimal,iftherelativehumidityinthebasementiscontrolled.
4.3 Constructability and Cost
Theconstructabilityofthiswallsystemisnotdifficult,butcareshouldbetakenthatairisunabletogetbehindtheXPS.Thiscouldbeaccomplishedwithtape,caulking,cansofsprayfoamoracombinationofthethree.Itisnotlikelythattapewillmaintainagoodairsealforthedesiredlifetimeofthewallsystem.ThiswallperformssignificantlybetterthanCase3,atonlyasmallincreasedcost.
4.4 Other Considerations
ThiswallconstructionisanimprovementoverCases2and3,butthereareevenbetteroptionsforthermalandmoisturecontroldiscussedinthefollowingCases.Thisisanaffordableoptionthatmanypeoplecoulddothemselves,withsignificantlylessmoisturerelatedrisksthanCases2and3,resultinginamorecomfortableandhealthyspace.
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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.
5.2 Moisture Control
Providedthataircannotbypasstheinsulationlayers,thisstrategywillnotexperienceanymoisturerelatedissuesfromvapordiffusion,orcapillarywicking.Capillarywickingislimitedbythethermal/capillarybreakattheedgeoftheslab,andspecifiedontopofthefooting.
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5.3 Constructability and Cost
Theseamsinthetwolayersoffoaminsulationshouldbeoffsetandwellsealed.Athermalbarrierisrequiredbycodeinmostjurisdictions.Thermax™byDowisafoilfacedpolyisocyanurateinsulationthatiscodecompliant.
Tofinishthebasement,drywallwouldbeadded,whichobviatestheneedforfirecontrolinthefoam.
5.4 Other Considerations
Astudwallwillstillneedtobeconstructedtofinishthisbasementwithservicesanddrywall,soifthelongtermplanistofinishbasement,thisproposedwallsystemmaynotbethemosteconomicalchoice.
Insteadofusingtwodifferentboardfoaminsulations,itcouldbeconstructedwithtwolayersofPIC,ortwolayersofXPSwithdrywallinteriorfinish.
Thisbasementinsulationstrategyisrecommendedasadurable,comfortable,andhealthybasementsystem.
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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.
6.2 Moisture Control
Becauseclosedcellsprayfoamisanairandvaporbarrier,therearenoriskstoairleakageorvapordiffusioncondensation.Theconcreteisunabletodrytotheinteriorthroughclosedcellsprayfoam,butconcreteisgenerallynotaffectedbyahighmoisturecontent.Figure21showstherelativehumidityinthemiddleofthefoamdoesnotexceed80%,whichmeanstherearenomoisturerelatedrisksfromvapordiffusion.
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6.3 Constructability and Cost
Inthisproposedwallsystem,itispossibletoembedtheframingmembersinthefoam(similartoCase10,toincreasetheinteriorspace.Theframingshouldnotbeincontactwiththefoundationwalltolimitthermalbridging,andpotentialmoisturerelatedissueswiththeframingmembers.Closedcellsprayfoamcanbemoreexpensivethanotheroptions,butreduceslabourtimeoversomeoftheotherwalls,andisappliedbyaskilledlabourersothesystemisverydurableasalongtermsolution.
Sprayonthermalbarrierscanaddsignificantcosttothesprayfoaminstallation,butareregionspecific.
Closedcellsprayfoaminstalledontheinterioroftheconcretefoundationwallistheeasiestandsafestwaytoretrofitanexistingbasement.Sprayfoamcanbeinstalledincombinationwithadrainagemattandinteriordrainagetileinbasementsthathaveliquidwateringressissues.
6.4 Other Considerations
Sprayfoamshavebeenimprovedconsiderablyforhumanhealthandtheenvironment.Ozonedepletingsubstancesintheprocesshavebeenremoved,butsomesprayfoamsusegreenhousegasesthataremuchworsethancarbondioxide.Thereareoptionsavailableofmoreenvironmentallyfriendlysprayfoamsthatdonotreleasegreenhousegases,suchaswaterblownfoams,onthemarketandshouldbeconsidered.
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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.
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7.2 Moisture Control
Opencellsprayfoamisanairbarrier,butisvaporpermeable.Figure40showstheXPSinsulationdetailrequiredattheabovegradeportionofthefoundationwallforcoldclimateconstructiontominimizemoisturecondensationatthecoldconcreteinthewintermonths,andminimizeinwarddrivenvaporinthesummermonths.
Therelativehumiditywaspredictedinthecenteroftheopencellsprayfoaminsulationandwasfoundtobeatsafelevels(Figure24).
Lowpermeanceinteriorwallfinishes(<ClassIII)shouldbeavoidedwiththisconstructionstrategysothematerialcharacteristicsofthesprayonthermalbarriermustbeconsidered.
7.3 Constructability and Cost
Opencellsprayfoamislessexpensivethanclosedcellsprayfoambutdoesdecreasetheinteriorusefulspaceandvaporcontrolshouldbeconsideredforthissystem.
Thisproposedwallsystemdoesnotallowforfinishingofthebasementwithoutinstallinganinteriorframedwall.Ifthelongtermgoalistofinishtheinteriorofthebasement,Case10shouldbeconsideredinstead.
Sprayonthermalbarrierscanaddsignificantcosttothesprayfoaminstallation,butareregionspecific.
7.4 Other Considerations
Thisisarecommendedwallconstructionprovidedthatthedetailsforcoldclimatesarefollowed,includinganextralayerofvaporcondensationprotectionfortheabovegroundportionofthewall.
Sprayfoamshavebeenimprovedconsiderablyforhumanhealthandtheenvironment.Ozonedepletingsubstancesintheprocesshavebeenremoved,butsomesprayfoamsusegreenhousegasesthataremuchworsethancarbondioxide.Thereareoptionsavailableofmoreenvironmentallyfriendlysprayfoamsdonotreleasegreenhousegases,suchaswaterblownfoams,onthemarketandshouldbeconsidered.
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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.
8.2 Moisture Control
Thewatervapordiffusionandcapillarywickingarecontrolledby2”ofXPSinsulationassumingthattheXPSiswellsealedtotheconcrete.ThiswallsystemwasnothygrothermallysimulatedsinceitwillperformbetterthanCase14fromamoisturepointofview,andCase14performedwell.Case14has5.5”offiberglassbattinsulationwhichwillresultincoldercondensationplane.Case14hadsomecondensationpotentialbutimprovedperformancewithavaporretardingpaint.Therewassomepotentialforairleakagecondensationattheabovegradesectionofthewallinthewinteralternatingwithdryingperiods.
8.3 Constructability and Cost
Itmaybedifficulttoget2”boardsofXPSattachedwelltothenonuniformsurfaceoftheconcretefoundationbecausetheinsulationissostiff.Itiseasierinsomecasestouse21”thickboards,thatwillflexoverimperfections.Thejointsintheinsulationshouldbeoffsetiftwolayersof1”XPSareused.
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8.4 Other Considerations
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.
9.2 Moisture Control
Thewatervapordiffusionandcapillarywickingarecontrolledby2”ofPICinsulationassumingthatthePICiswellsealedtotheconcrete.Thiswallsystemwasnothygrothermallysimulatedsinceitwillnotexperienceanymoisturerelatedissues.Thefoilfaceonthepolyisocyanuratewillnotallowvapordiffusionfromtheconcretefoundation,andtheincreasedR‐valueofPICcomparedtoXPSwillincreasethecondensationsurfacetemperaturecomparedtoCase8andCase14,resultingindecreasedcondensationpotential.
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9.3 Constructability and Cost
Fiberglassbattinsulationcouldbeusedintheplaceofcellulosetodecreasethecostoftheassembly.
9.4 Other Considerations
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.
10.2 Moisture Control
Opencellsprayfoamisanairbarrier,butisvaporpermeable.Therelativehumiditywaspredictedinthecenteroftheopencellsprayfoaminsulationandwasfoundtobeatsafelevels(Figure24).
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Lowpermeanceinteriorwallfinishesshouldbeavoidedwiththisconstructionstrategy.
10.3 Constructability and Cost
ThissolutionismorepracticalthanCase7iftheplanistofinishtheinteriorofthebasement.
10.4 Other Considerations
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
11.1 Thermal Control
ThisproposedwallsystemhasaninstalledinsulationR‐valueofR20andresultsinheatingenergylossof19.43MBtusforthespecificchosenparameters.Theadvantageofinsulatingontheexterioristhattheinsulationontheexteriorofthefoundationcanbejoinedwiththeexteriorinsulationonthefirstfloor,whichformsacontinuouslayerofinsulationandvaporcontrol.Thethermaldisadvantageofthissystemisthatthereisathermalbridgethroughtheconcretewall,andfootingintotheground.
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11.2 Moisture Control
FourinchesofXPSisagreatvapordiffusionresisterandcapillarybreakforinwardmoisturemovement.Thereisstillcapillarywickingpotentialthroughthefootingintotheinteriorsurfaceofconcreteresultinginmoistureattheinteriorsurfaceevaporatingintotheinteriorspaceifitisnotdetailedcorrectly.Thispotentialmoistureissuecanbesolvedbyusingacapillarybreak(eitherliquidappliedorplasticbased)onthetopofthefootingasnotedinthedesigndetails.Unlikesomeoftheotherproposedfoundationwallsystems,theexposedconcreteinthissystemwillprovidemoisturebufferingcapacity,onceithasdried.
11.3 Constructability and Cost
Thisproposedwallsystemwithexteriorinsulationisperceivedasdifficulttotheconstructiontrades,andthefinishingoftheabovegradeportionmaynotbearchitecturallydesirable.Insomecasesthetimingoftheinsulationinstallationtradescanbetrickysincetheentirehouseisnotinsulatedatonceinthiscase.
11.4 Other Considerations
Insomecases,exteriorfoundationisnotallowedbythebuildingcodeduetocomplicationswithtermitesandotherinsects.Whereinsectsmaybeanissue,Case12proposedwallsystemcouldbeused.
12. CASE 12 : 4” XPS INSULATION IN THE CENTER OF FOUNDATION WALL
Figure 45 : Case 12 – Interstitial XPS Insulation
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12.1 Thermal Control
ThisconstructionstrategyhasaninstalledinsulationR‐valueofR20,andhasapredictedannualheatingenergylossof19.24MBtus.Unlikesomeoftheotherwallsystemstheremaybethermalmassbenefitsoftheinteriorexposedsurfaceofconcrete.Thereisasmallthermalbridgethroughthefootingandinteriorsurfaceofconcretethatdoesincreasetheenergyrequiredoverawallthatisinsulatedcompletelyontheinterior
12.2 Moisture Control
FourinchesofXPSisagreatvapordiffusionresisterandcapillarybreakforinwardmoisturemovement.Thereisstillcapillarywickingpotentialthroughthefootingintotheinteriorsurfaceofconcreteresultinginmoistureattheinteriorsurfaceevaporatingintotheinteriorspaceifitisnotdetailedcorrectly.Thispotentialmoistureissuecanbesolvedbyusingacapillarybreak(eitherliquidappliedorplasticbased)onthetopofthefootingasnotedinthedesigndetails(Figure45).Unlikesomeoftheotherproposedfoundationwallsystems,theexposedconcreteinthissystemwillprovidemoisturebufferingcapacity,onceithasdried.
12.3 Constructability and Cost
Thisconstructionstrategyisnotverycommon,butisverydurablebecausetheXPSissealedintotheconcreteandprotectedfrominteriorandexteriordamage.Thiswalldesignismoreexpensivethaninstalling4”ontheinteriorortheexterior.
12.4 Other Considerations
Thisproposedwalltypemaynotbelocallyavailable.
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13. CASE 13 : INSULATED CONCRETE FORMS, 2” XPS ON INTERIOR AND EXTERIOR
Figure 46 : Case 13 –Insulated Concrete Forms (ICF)
13.1 Thermal Control
ThisconstructionstrategyhasaninstalledinsulationR‐valueofR20,andhasapredictedannualheatingenergylossof16.7MBtus.
13.2 Moisture Control
TwoinchesofXPSontheinterior,connectedtothethermalbreakattheslabedge,controlstheinteriorvapordriveandcapillarywickingtotheinteriorsotherearenomoisturerelatedissuesfrominwardvapordiffusionorcapillarywicking.
13.3 Constructability and Cost
Theinterioroftheinsulatedconcreteformwillrequiredrywallorotherthermalbarriertoachievethefireratingrequiredbycode.ThegypsumboardisveryeasytoattachtotheplasticclipsdesignedintotheICF.Thedrywallshouldnotbepainted,ifitisnotnecessary,toallowmaximumdryingoftheconcrete.Itmaybeeasierandmorepracticaltoinstallathinframedwall(eg.2x3woodorsteelframing)ontheinterioroftheICFtoallowanynecessaryservicestoberuninthewall,andpotentiallymoreinsulation.
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13.4 Other Considerations
Becausetheconcreteisinstalledbetweentwovaporretardinglayers,itwilltakeseveralyearsfortheconcretetodrytoequilibrium.Sinceadditionalinteriorvaporcontrolshouldbeavoided,nomorethanlatexpaintshouldbeusedontheinteriorsurfaceofthedrywall.
14. CASE 14 : 2” XPS, 2X6 FRAMING WITH FIBREGLASS BATT
Figure 47 : Case 14 – 2”XPS, 2x6 framing with fiberglass batt
14.1 Thermal Control
ThisfoundationwallsystemhasacalculatedparallelpathR‐valueofR28.7,andayearlyheatingenergyconsumptionof14.79MBTusassumingR10undertheslabandinthethermalbreak.Onlyiftherestoftheenclosureissuperinsulated,andairtight,inaverycoldclimatewillitmakesensetoincreasetheR‐valueofthefoundationwall.ItmaymakesensewithanR30foundationwalltoincreasetheunderslabinsulationtoR15orR20.Thisshouldbeexaminedinmoredetail.
14.2 Moisture Control
ThiswallwasanalyzedinWUFItopredictthemoisturerelatedriskinthewallsystem,anditwasshownthattheRHatthesurfaceoftheXPSintheabovegradeportionofthewalliselevatedinthewintermonths(Figure28),andthatthereissomecondensationpotentialalternatingwithperiodsofdryingpotentialatthetopofthefoundationwall.(Figure27).ThereislittleriskofmoisturerelatedissuesinthisallsystemiftheinteriorRHiscontrolledwithadehumidifier,andtheinteriordrywalliswellairsealed.
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14.3 Constructability and Cost
ThiswallsystemisslightlymoreexpensivethanCases8and9byincreasingthedepthoftheframedcavitywith2x6framinginsteadof2x4framing.Itispossibletouse2x4framingstoodoutfromtheXPSby2inches,anduseR19fiberglassbatts,orblowncelluloseorfibreglass.R19fiberglassbattsshouldbelessexpensivethanR13fiberglassbattsbecausethemanufacturingprocessforbothR19andR13battsusesthesameamountoffibreglass,buttheR13battsrequiremoretimeandefforttocompactto3.5”makingthemmoreexpensivetoproduce.
14.4 Other Considerations
15. CASE 15 : 4” PIC, 2X6 FRAMING WITH FIBREGLASS BATT
Figure 48 : Case 14 – 2”XPS, 2x6 framing with fiberglass batt
15.1 Thermal Control
ThisfoundationwallsystemhasacalculatedparallelpathR‐valueofR45.0,andayearlyheatingenergyconsumptionof11.09MBTusassumingR20undertheslabandinthethermalbreak..ThisisthehighestRvaluefoundationsysteminthisstudy,andislikelynotcosteffectiveunlesstherestofthehouseissuperinsulatedandairtight.
15.2 Moisture Control
ThiswallwasanalyzedinWUFItopredictthemoisturerelatedriskinthewallsystem,anditwasshownthattheRHatthesurfaceoftheXPSintheabovegradeportionofthewallisslightlyelevatedinthewinter
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months(Figure31),butdoesnotexceed90%.Thereisalmostnocondensationpotential(Figure32)exceptontheupperwallofthenorthorientationfortwoveryshortperiods.ThereisvirtuallynoriskofmoisturerelatedissuesinthisallsystemiftheinteriorRHiscontrolledwithadehumidifier,andtheinteriordrywalliswellairsealed.
15.3 Constructability and Cost
ThiswallsystemisslightlymoreexpensivethanCases14bychangingthe2”ofXPSto4”offoil‐facedpolyisocyanurate.Itispossibletouse2x4framingstoodoutfromtheXPSby2inches,anduseR19fiberglassbatts,orblowncelluloseorfibreglass.R19fiberglassbattsshouldbelessexpensivethanR13fiberglassbattsbecausethemanufacturingprocessforbothR19andR13battsusesthesameamountoffibreglass,buttheR13battsrequiremoretimeandefforttocompactto3.5”makingthemmoreexpensivetoproduce.
15.4 Other Considerations
Dependingonsitespecificconditions,andlocalcosts,thiswallislikelynoteconomicaltobuildunlessthehouseisveryhighlyinsulatedandairtight.
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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.
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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.
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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
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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
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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.
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