structure , home inspection course and exam , north america , canada
TRANSCRIPT
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Structure
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INTRODUCTION
1.0WhyBuildingsMove
GRAVITY What causes structures to
move? In a word, gravity.
Gravityisconstantlyworkingtogetthingsclosertotheground.
Strongstructuresresistgravity.
STRUCTURE Therearetwocommonwaysa
structuremaygiveintogravity.
FAILURES a)If it is sitting on something
thatisnotstrongenough,the
groundbelowitwillfail.Bet-
tertobuildonbedrockthan
quicksand.
b)Ifthestructureitselfisweak,
itwillnotsupporttheloadsimposedonit.Thetotalload
ismadeupofthefollowing
Deadloadtheweightofthestructureitself, Liveloadfurniture,people,wind,snow
andearthquakes.
WIND Windactsintermittentlyonstructures.Windforcescanpush,pullorliftbuildings.Buildings
mustbestrongenoughtoresistthelateralandupliftforcesofwindaswellasthedownward
forceofgravity.Hurricanesandtornadoesareextremewindconditions.Theseoftenresultin
mechanicaldamagecausedbyprojectiles.
The structure of a home is the skeleton, which includes the foundations and footings as well
as the floors, walls, and roof. Structures are judged by how well they are able to stand still.
Successful structures do not move; unsuccessful ones do, sometimes dramatically.
In this section we will describe the purpose of the structure, and then look at all the structural
elements. Where there are several types, we will briefly outline each. We will describe what the
components do, what can go wrong, and what that means to the home.
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EARTHQUAKES Earthquakesalsocreateforces,whichcancausestructuralfailures.Likewind,theseforcesare
ANDEROSION intermittentandvariableandcanpush,pullorliftbuildings.Erosionisaslowerformofearth
movement,butitcanhaveadevastatingeffectonstructuresaswell.
COMPONENT House components may fail because theywere poorlybuiltwith impropermaterials, or
FAILURES thematerialswerepoorly assembled.Rot,insects,reandmechanicaldamagecan causewell-builtstructurestofail.Rustcanattackmetalcomponents.
COMPRESSION Whatforcesaffectindividualstructuralcomponents?Thetwobasicforcesarecompression
ANDTENSION andtension.Amaterialisundercompressionwhenitisbeingpushedfrombothends.Amate-
rialisundertensionifitispulledon.Componentsincompressiontendtogetshorterorare
squashed.Componentsundertensiontendtogetlongerorarepulledapart.Manybuilding
componentsfeelacombinationofcompressionandtension.
Somebuildingmaterialsare good in compression,othersworkwell in tensionandsome
perform well inboth.A pile ofbricks is very good in compression; you can standon it.
However,itisverypoorintension.Achildcanpullthepileapart.Achain,ontheotherhand,
isverygoodintension.Youcanpullquitehardonbothendsandnothingwillgive,butthe
momentyoutrytopushonit,thechaincollapses.Itisnotverygoodincompression.
SHEARINGAND Differentmaterialsfailindifferentways.Shearingandbendingarecommonmodesoffailure.
BENDING Shearoccurswhenadjacentfacesofamaterialmoveinoppositedirections.Whenabeam
splits,orabrickcracks,itisbecauseofshear.
Bendingismovementwithoutshearing.Aplankspannedbetweentwochairswillbendifsome-
onestandsonit,particularlyiftheystandnearthemiddle.Theupperhalfoftheplankispushed
togetherundercompression;thebottomhalfgetsslightlylongerbecauseitisintension.
Buildingcomponentsthatfailbybendingaresaidtosagorbuckle.Somematerialscanbend
asignicantamountwithoutlosingtheirstrength.Brittlematerials,however,donotbend
muchbeforetheybreak.Ductilematerialsdo.Ceramictileisbrittle,ropeisductile.Someductilematerialsareelastic.Thismeanstheywillgobacktotheiroriginalshapeafterbeing
bent.Arubberballiselastic;anailisnot.
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DEFLECTION Deflectionisamildformof
bending. If structures deect
justalittle,peopledonotmind.
Building codes stipulate how
muchdeectionisacceptable.A
typicaloor joist, forexample,
isallowedtodeect1/360thof
itsspan.
MATERIAL What makes a good building
SELECTION material? Itshould begood at
resisting the forces of tension
and compression. It should be
cheap, easy toworkwith, light,
long lasting,water, rot and re
resistant,andstableunderdiffer-
enttemperatureandhumiditylevels.Noonematerialdoesitall.Thatiswhyhousesaremadeofmanymaterials.Woodisoneofthebettermaterialsforsmallbuildings.Itisrelativelygoodinboth
tensionandcompression.Steelisalsogoodinbothtensionandcompression.
Buildingmaterialsarechosenbasedoncost-effectiveness.Thegoalistoassembleastructure
thatwillperformwellforassmallacostaspossible.Thiscanleadtosomeverysmallmargins
ofsafetyand,ofcourse,somefailures.Asnewmaterialsaredeveloped,theyaretried;insome
cases,withgreatsuccess;inothercases,withverypoorresults.
Thestructureisbyfarthemostimportantpartofthehouse.Thesafetyandusabilityofthe
entirehomedependsonitsstructuralintegrity.Sincemanystructuralcomponentsareburied
belowgradeorbehindnishes,muchofthestructuralinspectionisdonebylookingforevi-
denceofmovement.Wherenomovementhasoccurred,imperfectionsmaygoundetected.Newinteriororexteriornishesandpatchingworkmayconcealimperfectionsovertheshort
term.Inthesecases,problemswillnotbeidentied.
REPAIRS Structuralrepairscanbeverycostly,andinsomecasestheproblemissoseverethatthebuild-
ingistorndown.Inmanycases,astructuralengineershouldbeconsultedbeforemaking
repairs.Anincompleteunderstandingofaproblemmayleadtoincorrectsolutionsandalife-
threateningsituation.
CHAPTER In this chapter well look at foundation congurations briey, then discuss the various
ORGANIZATION structurecomponentsoneatatime,startingwiththefootingsandnishingwiththeroof.
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2.0Confguration
Homesmayhaveabasement,acrawlspace,both,orneither.Manyhouseshavepartialbase-
mentsand/orpartialcrawlspaces.Thecongurationisdeterminedbyclimate,cost,regional
buildingpracticesandrestrictionsimposedbythebuildingsite.Inareaspronetohurricanesandooding,buildingsmaybebuiltonpostsorstiltstokeepthehomewellabovegrade.
2.1Basement
Wherefrostfootingsarerequired,atrenchisneededaroundthehouseperimeterforthe
footingandfoundationsystem.Sincethisexcavationisnecessary,itisnotmuchmoreexpen-
sivetodigabigholeandcreateabasement.Inwarmclimateswherefrostfootingsarenot
required,basementsarerare.
Thebelow-gradespaceisinexpensivetobuildoncetheholeisdug,andcanbeusedforany-
thingfromroughstoragetolivingspace.Basementscommonlycontainthemechanicaland
electricalsystemsandmayincludeaworkroomandlaundry(althoughthelaundryisupstairsinmanymodernhomes).Gameroomsandfamilyroomsareoftenlocatedinbasements,and
completeapartmentscanalsobebuiltbelowgrade.
Disadvantagesofbasementsincludethesusceptibilitytowaterleakageandlackofnatural
light.Windowsinbasementsareusuallysmallandhighonthewall,sincemostofthewallis
underground.Basementceilingsareoftenlow,andevenifthereisnowaterleakage,theycan
becoolanddamp.
2.2Crawlspace
Whereatrenchisdugforthefoundations,andtheearthunderthehouseoorisnotremoved,
acrawlspaceiscreated.Itmayhaveanearthoor,althoughaconcreteslabismoredesirable
forstorageandmoisturecontrol.Manymoderncodescallforcrawlspacestobe36 inches
highwhereaccessmustbegained,althoughmanyoldcrawlspacesareless.Someareentirely
inaccessible.Restrictedaccessmakesinspection,maintenanceandrepairmoredifcultand
expensive.
VENTING Crawlspacesareoftenignoredfor longperiods.Wheremoisturelevelsarehigh,structural
damage,duetorotandinsectactivity,cangounnoticed.Somebuildingstandardscallforone
squarefootofventingforevery500squarefeetofcrawlspacearea.Thisisrarelyprovided.
Wherethecrawlspaceisdry,thismaynotbeaproblem.
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2.3Slab-on-Grade
Inthistypeofconstruction,apouredconcreteoorrestsdirectlyontheground.Theconcrete
slab is at least three inches thick and may ormay not be reinforced with steel bars.
Immediatelybelowtheslab,amoisturebarrieristypically laidoveraboutsixinchesof
gravel.Inmodernconstruction,insulationisoftenprovidedbelowtheslab.Slabsaretypically
supportedbyfootingsandfoundations.
Thereareseveraltypesofslab-
on-grade construction, includ-
ingmonolithicslab,supported
slab,andoatingslab.Amono-
lithicslabisaconcreteoorand
foundation all poured as one.
Thiscanbethoughtofasaoor
slab that is thicker around the
edges.Asupportedslabisnotpoured
together with the founda-
tion, but it does rest on the
foundation. The footings and
foundation wall are installed
rst,withaledgeatthetopof
the foundation to support the
slab. Basement oor slabs are
oftensupportedslabs.
Theoatingslabisentirelyinde-pendentofthefoundation.The
foundation is poured or built
rst.Theslabisnotsupported
byorconnectedtothefounda-
tion.Thistypeofslabiscommon
ingarages.
From an inspection and main-
tenance standpoint, slab-on-
grade is more restrictive than
homes with basements or
crawlspaces because none ofthefoundationisaccessible.
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SYSTEMS Basementorcrawlspaceoorsareoftenleftasexposedconcrete.Problemswithwateror
CONCEALED insectinfestation,forexample,canbepickedupearly.Withslab-on-grade,theconcreteslab
isnormallycoveredbysubooringandnishooring.Problemscangoundetectedforsome
time.
Wheretheslabispoorqualityconcrete,toothin,ormissingthereinforcingbar,theoorispronetocrackingandshifting.Subsurfaceerosioncanalsoresultinslabfailure,ascanareas
excavatedforplumbingorheatingpipes.This leadstobroken,unevenoorsurfaceswith
morepointsofentryforwaterandinsects.Substantialshiftingcandamagetheplumbing,
heatingandelectricservicesburiedinorbelowtheslab.Expansivesoilscanheavetheslab,
resultinginsimilarproblems.
3.0Footings
Thefunctionoffootingsistotransmittheweightofthehousetothesoil,withoutallowing
thehousetosink.Footingsarelocatedbelowthefoundationwalls,orattheperimeterof
slabs,andbelowcolumnsorpiers.Thehorizontalsurfaceof thefootingis largerthanthe
foundation,sotheloadofthehousecanbespreadoutoverawidearea.Footingsaretypically
16to24incheswideandsixinchesto16inchesthick.Incoldclimates,footingscarrythehouse
loadsbelowthefrostline.Theheavierthebuildingandtheweakerthesoil,thelargerthe
footingshouldbe.
Footingsmaybeconcrete,brickorstone.Inmodernconstruction,mostfootingsarepoured
concrete,oftenreinforcedwithsteelbars.
FOOTINGTYPES Stripfootings(alsocalledspread
footings) run continuously be-
low foundationwalls, typically
around thebuilding perimeter.
Pad footings (also called spot
footings)aresmaller and typi-
callysupportcolumnsorpiers.
PIERAND Pier andgrade beam construc-
GRADEBEAM tioniscommoninareaswithex-
pansivesoils.Concretepiersare
poureddowntoadepthwhere
the soils are stable. Grade
beams,whichoftenformfoun-
dationwalls,spanbetweenthepiers. These grade beams are
oftenreinforcedconcrete.
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CommonProblemswithFootings
Whenthefootingsfail,theentirehousemoves.Thisisoftenaveryseriousproblem.Itis
almostalwaysexpensive,andsometimesimpossible,tocorrect.Sincethefootingsarelocated
belowthesoil,theycannotbeseen.Itisoftendifculttoknowwhytheyhavefailed.
Settlementisthemostcommonformoffailure,althoughheavingiscommonincoldclimates
duetofrostexpandingthesoilbelowfootings.
Sometimes footingsfail inone
area, and in most cases the
failure is notuniform, (i.e. the
building doesnot sink straight
downbutleans toone sideor
another).Often,onepartofthe
housewill pull away from the
rest. This leads to cracking of
interior and exterior wall sur-
faces.
SETTLEMENT Soils prone to compaction or
WEAKSOILS movementdonotsupportfoot-
ingswell.Thisincludesrecently
disturbedsoil.Forexample,ifan
excavation for a foundation is
dugtoodeep,thenbacklledtothecorrectdepth,thedisturbedsoilunderthefootingis
likelytocompactovertherstfewyears,resultinginbuildingsettlement.
SETTLEMENT This is not common on pro-
ABSENCEOF fessionally-built houses, but
FOOTINGS may occur in casual construc-
tionaswellasonporchesand
poorly built additions. Some
homeswerebuiltonmudsills
woodbeamslaidontheground
with walls built on top of the
beams. Thesemud sills are re-
placed with a foundation and
footing system as the sills rot,
heaveorsettle.
SETTLEMENT Thesemayerodeorweakensoil
UNDERGROUND below the footings, causing
STREAMS severebuildingsettlement.Itis,
ofcourse,verydifculttolocateandtraceundergroundstreams.Theyoftenowonlyat
certaintimesoftheyear.
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SETTLEMENT Settlementmaybetheresultofpoordesign,oranadditionalloadthathasbeenadded.
UNDERSIZED For example, when a second oor is added to a bungalow, the weight may cause the
FOOTINGS footingstosink.Theadditionalweightofamasonrychimneycanalsocauselocalizedfooting
failure.
SETTLEMENT Thefootingmustbestrongenoughnottobreakapartunderaload,andmustbeabletostand FOOTING uptocontinuousexposuretodampsoil.
DETERIORATION
SETTLEMENT Ifthebasementoorislowered,thereistheriskthatthefootingswillbebrokenoffonthe
UNDERMINED insideorwilllosetheirsupport.Evenifexcavationisnotdonebelowthefootingsbutdown
ORCUT tothebottomofthem,thelateralsupportforthefootingmaybelost,andthefootingand
FOOTINGS foundationwallmaymoveinward.
SETTLEMENT/ Whenabasementoorislowered,thefootingsshouldbeunderpinned(loweredand,insome
WALLFAILURE cases,enlarged).Alternatively,onlythecentralsectionofthebasementshouldbelowered,to
LOWERED avoiddisturbinganyofthesoilnearthefootings.Dependinguponhowmuchthebasement
BASEMENT oorislowered,therequiredclearancefromthefootingsvaries.Asoilsengineerisoften FLOORS consultedandaconcretecurb(alsocalledabenchfootingorDutchwall)maybeneeded
aroundtheinsideedgeofthefootingstoensuretheyarenotcompromised.Buildingsettle-
mentandfailureoffoundationwallsarebothriskswhenloweringbasementoors.
Oneofthedangersinloweringbasementoorsistheincreasedriskofbasementleakage.
Noticeinthefollowingillustrationshowthedrainagetileoutsideisnolongerinthecorrect
locationoncetheoorislowered.Itistoohightobeeffective.
Whenexcavationisdoneontheexterior,(e.g.foranadditionorswimmingpool)thefootings
canbedamagedorunderminedinasimilarfashion.
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SETTLEMENT Housesbuiltonorclosetoslopesmaybesubjecttofailuresasaresultofsoilmovingdown
LOTSLOPE theslope.Thismaybeaslowsteadyprocessorasuddeneventtriggeredbyheavyrainsfor
example.Thiscanbeextremelycostlytocorrect.
SETTLEMENT Houses builton slopinglotsmaybemoreproneto footing and foundation failures. The
CUTAND chancesofbuildingondisturbedsoilareincreasedonlotssuchasthese.Effortsmadetolevel FILLLOTS andterracethelotmayresultin
soilbeingcutoutofthehillto
form a level terraceunder the
backhalfofthehouse.Thissoil
isthenusedasllintheadja-
centareawhere thefront half
of the house is to stand. The
downhillhalfofthehousemay
bebuiltonllthatmaynotbe
wellcompactedormaynotbe
abletostayinplaceandsupportthehouse.
On sloping lots, large lateral
earth thrust and hydrostatic
pressurecanbebuiltupbythe
soilonthehighsideofthehome.
Waterrunningdowntheslopeisblockedbythebuildingandaccumulateshere.
Onthedownhillside,thefootingsmaynotbedeepenoughincoldclimates.Frostheavecan
resultwherethefootingsarelessthanfourfeetbelowgrade.Thesideofthehousewiththe
lowergradeoftenhasawalk-outbasement,andchancesofafootingbeingtooshalloware
greatesthere.
SETTLEMENT/ Someclaysoilsthatexpandandcontractsignicantlywithdifferentmoisturecontentsmay
HEAVING alsoresultinfailure.Theseexpansivesoilscanheaveoorsandfoundationswhentheyget
EXPANSIVESOILS wet.Whentheydry,theyshrinkandallowthebuildingtodrop.Thisisasignicantcauseof
housestructureproblemsinsomeareas.
Treerootscanaffect themoisturecontent of soils noticeably.Most soils have strengths
thatchangewithdifferentmoisturecontents.Someclaysoilstrengthschangedramatically.
Thesearepoorbuildingsoils.Siltsarealsopoorbuildingsoils,inmanycasesmuchweaker
thanclay.
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EXPANSIVE Whereexpansivesoilsarecommon,heavingsoilbelowtheslabcanpushtheslabupwards
SOILSAND atthecenterorattheperimeter,breakingtheconcreteanddamagingutilitylines.Where
SLAB-ON- thesesoilsarecommon,theslabsaresometimespost-tensioned.Thismeanstherearesteel
GRADEHOMES reinforcing cables laid within
theslabandprojectbeyondthe
slab edge. The cables are
tightened afterthe concrete is
poured to strengthen theslab,
helpingitresisttheforcesofthe
expansive soils. The slabs are
sometimesthickenedinplaces,
often with beams running in
both directions on the under-
sideoftheslab.Thesearecalled
ribbedfoundations.
The expansive soils below theslabareoftensaturatedduring
constructionbeforepouringthe
slabsothesoilswillbeamaxi-
mum height when the slab is
poured.
FROSTHEAVE Ifthefootingsandfoundationsarenotdeepenough,thegroundbelowthemmayfreeze.
FOOTINGSTOO Frozenground expands andmay pick upall orpart of the building. This can do serious
SHALLOW damage.
FROSTHEAVE Exteriorbasementstairwellsmaycompromisethefootingsincoldclimates.Inordertobe
OUTSIDE effective,thefootingsincoldclimatesmustbebelowthefrostlevel.Whenanexteriorbase- BASEMENT mentstairwellisadded,thestairwellopeningeffectivelylowerstheexteriorgradelevel,and
STAIRWELL alsolowersthedepthtowhichfrostcanpenetrate.Afterthestairwellisinplace,thefrostcan
goseveralfeetbelowthebottomofthestairwellopening.Thiscanleadtofrostheavingof
thefootingsandthefoundations.
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A properly added exterior stairwell will include deepened foundations, or a completely
insulatedapproach,topreventfrostpenetrationbelowthebuildingfootings.
IDENTIFYING Duringaninspection,theresultsoffootingfailurecanusuallybeseen.Itis,however,difcult
THEPROBLEM toknowwhetherthebuildingisstillmoving,andifso,atwhatrate.Itisoftennecessaryto
monitorthebuildingoveraperiodofmonthsorevenyears,toknowwhethertheproblemwill
warrantrepair.Manyfootingfailuresarenotsevereenoughtowarrantrepairs.
REPAIRS The usual corrective action is
UNDERPINNING to underpin the footings. This
meansdiggingunder theexist-
ing footing, and adding a new
footing wider and/or deeper
thantheoriginal.Thismayhave
tobedoneinsmallsectionson
strip footings sinceone cannot
excavateundertheentirehouse
atonetime.Usuallytwotofour
footsectionsaredoneatatime.
Thisisveryexpensivework.
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REPAIRSPILES Insomecases,wherethesoils
ANDHELICAL aremovingorarelikelytomove,
ANCHORS underpinning is not appropri-
ate. Piles driven deep into the
ground are an alternative, but
may not be cost-effective for
an existing building. Helical
anchorsaresometimesscrewed
into the soil to support failed
footings.
4.0Foundations
4.1General
Foundationstransmittheweightofthehousefromtheabove-gradewallsandoorsdown
tothefootings.Wherethereisabasementorcrawlspace,foundationsalsoresistthelateral
pressureof thesoil.Thefoundationactsasaretainingwall inthissense.In coldclimates,
foundationscarrytheweightofthehousebelowthefrostlinetopreventfrostheaving.
Typicalfoundationmaterialsarestone,brick,pouredconcrete,concreteblock,cinderblock,
insulatedconcreteforms,claytile,andwood.Mostofthesematerialsbehavesimilarly.Wood
foundationsaretheexception.
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COMMON Foundationsmaybecontinuouswalls(stemwalls),oftenmadeofconcrete,masonryblock
FOUNDATION orinsulatedconcreteforms(ICF).Foundationsmayalsobepierssupportedbypadfootings.
TYPES Whereoodingisarisk,homesmaybebuiltonpiersthatarewellabovegrade.Piersmaybe
belowgrade,andmaybeconnectedbygradebeams.
Wheresoilconditionsarepoor,thebuildingmayrestonpilesthataredrivenorturneddownintothegroundtosomedepthtoprovideadequatebearingstrengthtosupportthehome.
Twocommonfoundationarrangementsareillustratedbelow.
CommonProblemswithFoundations
CRACKS/ Foundationwallsmaycrack,bow,spallorshift.Cracksmaybeduetoshrinkage,settlementor
BOWING/ lateralforces.Somecracksareseriouswhileothersareinsignicant.Bowingisusuallythe
SPALLING resultoflateralforces.Spallingindicatespoorqualitymaterialsorchronicwaterproblems.
Someofthecausesoffoundationdefectsareoutlinedbelow.
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INADEQUATE Basement and crawlspace foundations are really retaining walls, holding back the soil
LATERALSUPPORT outside.Ifthefoundationsdonotprovideenoughlateralsupport,theywilldeectinwards.
This may be the result ofmechanical forces exerted duringback-lling; back-llingwith
frozensoil(coldclimatesonly);unusualfrostdevelopmentinthesoilimmediatelyoutsidethe
building (cold climatesonly); foundationwallsthatare toothin, tootall ordonothave
adequatereinforcement;orthehouseoorsystemdoesnotprovideadequatebracingforthe
topofthefoundationwall.Thislastproblemiscommononthehighsidewallonaslopinglot.
Bothmasonrywallsandpouredconcretewallscanfailifnotproperlybuilt.
INWARD Foundationwallsthatmoveinwardcanberepairedbytyingthembackfromtheoutside,
BOWING usingtiesandanchors.Alternatively,buttressescanbeprovidedontheinterior.Theseoften
areconcreteorconcreteblockstructuresbuiltagainstthebasementwalls.Steelbeamsare
sometimesused.Therearealsomodernstructuralfabricsthatcanbeappliedtostrengthenwalls.Anotherchoiceistobuildanewfoundationwallinsidetheold.Insomecasesthe
foundationisreplaced.
BOWING/ Mechanicaldamagecausedwhenbackllingduringconstructionforexample,cangenerally
CRACKS be repaired on a localized basis, although re-excavation is often necessary. Using heavy
MECHANICAL equipmentnexttothehome(tore-paveashareddriveway,forinstance)canalsoexerthigh
DAMAGE horizontalloadsandresultinbowingandcrackinginthefoundationsofoneorbothhouses.
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BOWING/ Theheightofsoiloutsideafoundationmayexertenoughforcetocausethefoundationto
CRACKS fail.Conventionalfoundationscantypicallytolerate3feetto71/2feetofsoilheightonthe
HEIGHTOF outside.Thestrengthofthefoundationisdeterminedbyitsmaterialconcreteorconcrete
BACKFILL blockforexample,thestrengthoftheconcrete,thethicknessofthewall,whetherthewallis
laterallysupportedatthetop,andwhetherthewallisreinforced.
BOWING/ Theforceexertedbylargetreerootsonthefoundationwallcanleadtodeectionofthe
CRACKSTREE foundations.Somesoiltypesshrinkconsiderablyastheydryout.Ifalargetreedrawswater
ROOTS fromsuchsoilsbelowafooting,
thefootingmaydropasthesoil
compacts.Inthiscase,thetree
damagesthehousewithoutac-tuallytouchingit.
Intheshortterm,treerootdam-
agecan bearrestedbycutting
down the treeand leavingthe
roots in place. Over the long
term,therootsmaybeexpected
torot,leadingtosoilsettlement,
resultant water leakage and,
in some cases, building settle-
ment.Therootsmayhavetobe
removed.
SPALLING/ Waterpenetrationcandeterioratethemortarinmasonryfoundations,reducingitsstrength
DETERIORATION andultimatelyallowingshiftingtooccur.Thisisusuallyaslow,long-termprocess.
WATER
PENETRATION
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SPALLING/ Waterrelatedproblemsandwalldeteriorationduetomoisturepenetrationcanbeminimized
DETERIORATION oreliminatedwithcontrolofsurfacewaterontheexterior.Goodexteriorgradingwithground
SURFACE slopingdownawayfromthebuildingisimportant.Properperformanceofguttersanddown-
WATER spoutsisequallyimportant.Allroofrun-offmustbedirectedintoadrainagesystemoronto
thegroundatleastsixfeetawayfromthebuilding.
SPALLING/ Wheregroundwateristheproblem(anundergroundstreamorhighwatertable),gradingand
DETERIORATION downspoutapproachesmaynotproveadequate.Drainagetilesand/ora sumpandpump,
GROUND areoftennecessary.Consultantsspecializinginsituationssuchastheseshouldbeengaged.
WATER SeeSection10intheInteriorchapter.
SPALLING/ Lowqualityconcretesubjected todamp soilsmay deteriorate,losingits strength.This is
DETERIORATION commoninpouredconcretefoundations,builtintheearly1900s.Theinteriororexteriorface
POORQUALITY oftheconcretemaycrumble(spall).Reducingmoisturepenetrationwillretardthisaction,but
CONCRETE ifthedamagehasprogressedtoapointwherethestructuralintegrityiscompromised,sections
ofthefoundationsmayhavetobecompletelyreplaced.Thisisanexpensiveundertaking.
SPALLING/ Somebricksaredesignedforusebelowgrade,butmanyarenot.Theuseofinappropriatebrick DETERIORATION willresultinashortenedfoundationlife.Ultimately,thebrickshavetobereplaced.
POORQUALITY
MASONRY
FOUNDATIONS Ifthefoundationwallsdonotextendwellabovegradelevel,thewallssittingontopofthem
TOOSHORT maybeexposedtodampsoilandrotordeteriorate.Foundationsshouldextendatleastfour
tosixinchesabovegradelevel.
CommonProblemsinColdClimates
FROSTHEAVE In coldclimates, if the foundationsare too shallow, frostmayheaveeven thebest-built TOOSHALLOW footingsandfoundations.Onslopedlots,thepossibilityofshallowfoundationsisgreateston
thelowside.Propertieswithbasementwalk-outsareoftenvulnerabletofreezingdamage.
FROSTHEAVE Conventionalcoldclimateconstructionassumesthehousewillbeheated.Anunheatedhouse
UNHEATED may have frost penetrating through the basement oor below the footings, leading to
HOUSES heaving.Thereisariskinvolvedinleavingahouseunheated.
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ADFREEZING Adfreezingisaphenomenon
wherebydampsoilontheout-
side of the building actually
freezes to thebuildingand as
the soil heaves, itwill lift the
toppartofthefoundationwall.
Horizontal cracks in founda-
tionwallsjustbelowgradeare
typical.
4.2WoodFoundations
Preservedwoodfoundationswereintroducedintheearly1960s.Severalthousandunitshave
beeninstalled.Lifeexpectanciesofthebelow-groundwoodareestimatedinthe50to100
year range, considerably less thanmany traditional building foundationmaterials. Some
manufacturersoffer60yearlimitedwarranties.
Thewoodischemicallytreated
to retard rot. Chemical treat-
mentforwoodusedinfounda-
tionsismoreintensivethanthat
typicallyusedinwoodfordecks,
fencing,etc.Thewoodfounda-
tions may rest on concrete orwood footings. With wood
foundations, special care must
be taken to ensure that the
foundation is able to perform
itsretainingwallfunction(ade-
quatelyresistinglateralforces).
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CommonProblemswithWoodFoundations
ROT/INSECT Rotandinsectdamagearethemajorenemiesofwoodfoundations.Woodfoundationsshould
DAMAGE notbeusedinareaspronetowood-destroyinginsectssuchastermites.
4.3PileFoundations
Pilesaresteel,woodorconcretecolumnsdrivenintothesoil.Theyareusedinweaksoilsand
mayextenddownthroughthepoorsoil,toreachasoilwithgoodbearingstrength.Pilesmay
dependonfrictionbetweenthe
sidesofthepileandthesoilfor
theirsupport.Theymayalsobe
point bearing at the bottom.
The building itself rests on
beamsorwallsthatstraddlethe
piles. Piles are expensive andoncethebuildingisup,thereis
often noway to know if piles
have been used and where.
Again,thepresenceorabsence
of building settlement is the
onlywaytodeterminehowsuc-
cessfultheapproachhasbeen.
PILESAND Insomeareas,garagesaretypicallyconstructedonpiles.Thepilessupportpouredconcrete
GRADEBEAMS gradebeamsforexample,whichinturn,supporttheoorandwallsystems.Thegarageooristhenpouredontheundisturbedsoil.
4.4PierFoundations
Wherecontinuousfoundationsarenotprovided,individualcolumnsorpiersmaybeusedto
supportabuilding.Thepiersshouldrestonafootingbelowthefrostlineincoldclimatesand
typicallythepiersupportsabeam.Thebeam,inturn,supportstheoor,wallandroofloads.
Piersarecommonlyfound inhouseswherethere isno basement ora partial basement.
A crawlspace often has a pier system supporting the structure above. Porches are also
commonlysupportedbypiers.
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Piersmaybestone,brick,con-
crete block, cinder block, or
wood. Most of these materi-
alsbehaveinasimilarfashion.
Wood, of course, is the most
vulnerable to rot and insect
damage. As a rule, wood/soil
contactisbestavoided.
Concrete piers are often used
with grade beams where ex-
pansivesoilsareanissue.
CommonProblemswithPiers
SETTLEMENT Pierproblemsareoftentheresultofinadequatefootings.Thiswillresultinsettlementofthe
INADEQUATE pierand,ofcourse,thebuildingabove.Ifthepierbaseisnotbelowthefrostlineinnorthern
FOOTINGS climates,frostheavingcanbeaproblem. Inboththesecases, thepiersusuallyhavetobe
rebuilt.Similarproblemscanresultinareaswithexpansivesoils.
OVERSPANNED Ifthepiershavetoogreataspanbetweenthem,thebeamsmaysagortheconcentrated
loadsmaycausethepierstosink.Addingpiersisthetypicalsolutionhere.
TOOSLENDER Ifthepiersaretooslenderorareoutofplumb,theymaynotbecapableofcarryingtheir
OROUTOF intendedloads.Diagonalwoodbracesareusedinsomeareastohelpholdpiersinplace.Piers
PLUMB thataredeterioratedasa resultofmoistureormechanicaldamageshouldbe repairedor
replacedasnecessary.Woodpierscanrot,beattackedbywood-boringinsects,reorbedamagedmechanically.
SKIRTING Preservedwoodperformsbetterthanmostspeciesofuntreatedwood.Wherepiersareused
inlieuofacontinuousfoundation,thespacebetweenthepiersusuallyhastobelledinto
preventsoilfromfallingintothebasementorcrawlspace.Inabove-gradesituations,skirting
keepsoutanimalsand,tosomeextent,rain,snowandcold.Skirtingmaybewood,masonry
orpouredconcrete,forexample.Wheretheskirtingisnotstructural,repairstodeteriorated
skirtingareoftendeferred.Woodskirtingoftendeteriorateswhereitcontactsthesoil.
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5.0Floors
Floorsprovidethebearingsurfaceforpeopleandfurniture.Theyalsotiethebuildingtogether,
addingrigidityandprovidingasurfaceforoorcoveringsaboveandceilingnishesbelow.
Wewilllookatoorcomponentsoneatatime.
5.1Sills
Woodsillsprovidealevel,continuouspadbetweenthefoundationtopandthebottomofthe
framingsystem.Thesillssecuretheoorsystemtothefoundation.
ANCHOREDTO Typically,theoorjoistsrestdirectlyonandaresecuredtothesill.Sillsshouldbeanchored
FOUNDATION tothefoundation.Thisisoftenaccomplishedusingboltsanchoredintothetopofthefounda-
tionwall,passingthroughthesillandsecuredwithawasherandnut.
Innew construction, the sill is
typicallyawoodframingmem-
ber(2x4or2x6)laidat.Inolder
construction it may be a sub-
stantialwoodbeam(e.g. 8x8).
Wood sills can support wood
framing members but should
not support brick or stone.
CommonProblemswithSills
CRUSHED Sills may be crushed as a result of concentrated loads. Steel posts built into wallswill
CONCENTRATED sometimescausethis.
LOADS
CRUSHED Ifthebeamsorjoistsaretooshort,andonlytheveryendrestsonthesill(lessthanoneinch,
INADEQUATE forexample),theconcentratedloadsmaycrushthesill. ENDBEARING
MOVEMENT Wherethesillsarenotsecuredtothefoundations,thereisdangerofthebuildingshifting
INADEQUATE duringhighwinds,whensignicantupwardsandlateralforcescanbegenerated.
ANCHORING
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ROT/INSECT Woodsillsclosetogradelevelaresubjecttorotandinsectattackbecausetheyarewetmuch
DAMAGE ofthetime.Soilistypicallydamp.Sillsmayrotandcrushundertheweightoftheframing
system.Thiswillweakenthestructure,allowingittosettleslightlyandbreaktheconnection
betweentheoorandfoundation.
5.2Beams
Beamscarryoorandwallloadshorizontallytothefoundations,walls,columnsorposts.
Beamsmaybewood(solid,built-uporengineered),plywoodorsteel.
CommonProblemswithBeams
SAG Undersizedoroverspannedbeamsmaysagorcrack.Thismayleadto failureoftheentire
OVERSPANNED framingsystem.Fortunately,thisrarelyhappens,andalmostneversuddenly.Overspanned
woodbeamscanusuallybeidentiedreadily,andpostscanbeaddedorthebeamcanbe
strengthened.
CRUSH/FALL Wheretheendbearingisinadequate,thebeamcancrushitselforitssupport.Thereisalso
ENDBEARING potentialforthebeamtoslipoffitssupport.Typically,threeinchesisconsideredaminimum
endbearingforbeamswhensupportedbymasonryorconcrete.
ROT/INSECT Woodbuildingcomponentsarevulnerabletorot,damage,insectattackandre.Rotand
DAMAGE insectdamagearecommonwherethereiswood/soilcontact.Beamsbelowgradeshould
have1/2inchclearancealongthesidesandattheendtoallowforaircirculation.
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DAMAGE/ Mechanicaldamagecanbedoneaccidentallyorintentionally.Woodbeamsthatarenotched,
NOTCHED/ cut or drilled are weakened. The location and size of the damage determines whether
DRILLED correctiveactionisnecessary.
TWISTING/ Rotationofwoodbeamsdueto
ROTATION warping or poor support isrelatively uncommon but can
lead to damage and ultimate
failure.
NAILINGAND Built-up wood beamsmay not
BUTTJOINTS beadequatelynailed.Normally,
nailsshouldbeprovidedindou-
blerows every 18 inchesalong
thebeam.Wherebuttjointsoc-
curinwoodbeams,theyshould
be located over the supports
or as follows: the butt joints
shouldbewithinsixinchesofthequarterpointofthespan.Forexample,ifthespanis12feet,
thejointshouldbewithinsixinchesofthethree-footmarkorthenine-footmarkofthespan;
(i.e.thejointsshouldbe2-1/2to3-1/2feetfromtheendsupports).
RUST Steelbeamsaresusceptibletorust,particularlyifthebasementisdamp.Steelshouldbe
paintedtopreventrust.Lateralsupportforsteelbeamsistypicallyprovidedbywoodstrap-
pingsecuredtothejoists.
LATERAL Lateralsupportforsteelbeamsistypicallyprovidedbywoodstrappingsecuredtothejoists.
SUPPORT Thereareseveralwaystoprovidelateralsupportforwoodbeams.Seetheillustrationbelow.
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SECURINGTO Steelbeamsmaybepoorlysecuredtoposts.Windupliftmaycausethebeamtoliftoffthe
POSTS post,orimpactmayshiftitsothatsupportisnolongeroffered.Thebeamandpostshouldbe
bolted,weldedorclippedtogeth-
er. In hurricane or earthquake
areas, additional fastening may
be necessary. Special straps are
usedtoaccomplishthis.
STRENGTH A visual inspection of a steel
beam cannot determine its
strengthbecauseitdependson
morethansize.Theshapeofthe
beam,thelengthandthickness
of both the anges and web,
andtheweightperlinearfoot,
all inuence beam strength.
Thecarboncontentofsteelalsoaffectsitsperformance.
STEELVERSUS Steelbeamscanbemuchstrongerthanwoodbeamsandaremoreresistanttorot,insectand
WOOD mechanical damage, but are more expensive, heavier, and more difcult to work with.
Engineeredwoodbeamscanbestrongerthansolidwood,yetarelight,easytoworkwithand
lessexpensivethansteel.Woodbeamscanbecutonsitemoreeasilythansteel.Steelbeams
shouldrestonsteelpostsormasonry.Woodbeamscanrestonwoodmembers.
FIRE Fireisaconcernwithbothwoodandsteelbeams.Interestingly,asteelbeamwillloseits
strengthmuchearlierinarethanawoodbeam,althoughawoodbeamburnsandasteel
beamdoesnot.Steellosesitsstrengthafterbeingexposedtotemperaturesof1000F.for
aboutfourminutes.Steelbeamssaglikespaghettiduringare,allowingbuildingstocollapsequickly.Woodburnsbutlosesitsstrengthmuchmoreslowly.
5.3PostsandColumns
Posts or columns (two names
for the same thing) carry the
load of the beam vertically
downtothefootings.Theymay
bebrick,concreteblock,poured
concrete,wood,orsteel.
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CommonProblemswithPostsandColumns
SPALLING/ Masonrypostsmaybedeterioratedasaresultofmoistureorpoormortar.Risingdampisa
MORTAR common problem with brick columns. This is characterized by deteriorated mortar and
DETERIORATION eforescence(whitesaltydeposits)onthebottomofthepost.Insomecases,thebrickitself
deteriorates(spalls).
OUTOFPLUMB Poststhatareoutofplumbloseagooddealoftheirstrength.Generallyspeaking,ifthe
columnisoutofplumbbyroughlyone-thirdofitsthickness,theremaybeconcernaboutits
integrity.
RUST Rustonsteelpostscanbeaconcern.Thisisoftenaseriousproblematthebottomofthepost
inachronicallyoodingbasement.Rustwillquicklyreducetheloadcarryingcapacityofa
steelpost.
ROT/INSECT Woodpostsarevulnerabletorotandinsectattack.Thisisespeciallytruewherethepost
DAMAGE penetratesthebasementoorslab.Correctiveactionoftenincludessimplycuttingoffthebottomofthepostandplacingitonaconcretepad.
FOOTING A sinking post isusuallythe resultof amissing or inadequately sizedfooting.Obviously,
MISSINGORTOO suitablefootingsshouldbeprovided.Everypostorcolumnshouldhaveafooting.Thesecant
SMALL typicallybeseenoncethehomeisbuilt.
UNDERSIZEDOR Columncollapseissomewhatunusualbutisnormallytheresultofanundersizedcolumnor
DAMAGED onethathassufferedmechanicaldamage.
NOTWELL Apostthatisnotwellsecuredtothebeamabovecanallowthehousetoshiftduringwind
SECUREDTO upliftforces.Thebeamshouldalsobesupportedlaterallytopreventitfrommovingsideways.
BEAM SeeSection5.2.
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5.4FloorJoistsandTrusses
Thefunctionoftheseframingmembersistocarryandtransferloadsfromtheoorstothe
foundations,beamsorbearingwalls.
5.4.1ConventionalWoodJoists:Joistsaretraditionaldimensionallumber,typically2x8,2x10,or2x12.Thesehorizontalmemberscanbe12to24inchesapart,although16inchesisthemost
common.Theyarelaidonedge
sothatthesubooringisnailed
tothetwo-inchside.Floorjoists
should extend at least 1-1/2
inches onto the foundation or
beamateitherend.
JOISTSTRENGTH The strength of a joist comes
largelyfromitsdepth.Doubling
ajoistbyputtinganotherofthe
samesizebesideitwilldoubleits resistance to bending.
Doubling the depth of a joist
increasesitsresistancetobend-
ingbyeighttimes!Forexample,
the equivalent strength (con-
sideringdeectiononly)oftwo
2x10s compared to four 2x8s
canbecomparedbymultiplying
thebasetimestheheightcubed.Itisinterestingthattwo2x10saremoreresistanttobending
thanfour2x8s.
Thedeectionof aoorand joistsysteminmodernconstructionmaybequitesurprising.
Manycodesallowaoortodeect1/360thofitslengthundernormalloadingifthereisa
nishedceilingbelow.Forexample,thefollowingsituationisacceptablebymanycodes:2x10
oorjoistsspaced16inchesoncenterspanabout15feet.Whentheroomisoccupiedwith
furnitureandpeople,thecenterpartoftheoorcanbe1/2inchlowerthantheooredges.
Thisiscompletelysafe,andtheoorisnotatriskoffailing.However,thismaynotbesatisfac-
torytosomehomeowners.Codesareaminimumstandard.Brittleoornishingmaterials
likeceramictilemaynottolerateaexlikethis.Morerigidoorsareoftenusedwherethe
ooringmaterialisbrittle.
SPRINGYOR Floors are often bouncy or springy when people walk across a room, but this is not
BOUNCYFLOORS necessarilyindicativeofproblems.Lightframingcausesthiscondition,andwhiletheoorcan
bestiffened,thisisrarelydone.
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CommonProblemswithConventionalWoodJoists
OVERSPANNED Floorjoiststhatareoverspanned(undersized)arepronetosagging.Theacceptablespanof
ajoistisdeterminedbytheloaditwillcarry,thespeciesandgradeoflumberused,thedepth
of the joist, and the spacing
between joists. Over spanning
canbereadilycorrectedbyadd-
ing joists, or adding a beam
belowthejoistsinmostcases.
The implication of over span-
ning is typically a noticeable
sag,andinsomecases,abouncy
oorsystem.
DAMAGE/ Mechanicaldamageto joists is
NOTCHED/ common. Joists are commonly DRILLED notched,drilledandcutthrough
toaccommodateheating,plum-
bing and electrical systems. In
somecases,joistsarecutaround
stairwells to improve head-
room.Somedamageistypical,
andthereareseveralguidelines
onacceptablelimits.Joistsaresometimesnotchedattheendtorestonabeamorfoundation
wall.Thiscanweakenthejoistconsiderably.Thejoistusuallycrackshorizontallyfromthetop
ofthenotchtowardsthemid-pointofthespan.
INADEQUATE Joistsmaybepronetocrushingattheendsand/orslippingoffthebeamorfoundationwhere
ENDBEARING thereislessthan1-1/2inchofendbearing.
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JOISTHANGER Metalbracketscalledjoisthangersareusedwherejoistscannotrestonasupport.Here,the
PROBLEM joistsarecradledinandnailedtothehangers,whichare securedto thesideofabeamor
header.Joisthangersmaybeundersizedorinadequatelynailed.
ROT/INSECT Rotandinsectscanattackanywoodcomponents.Joistendsclosetooutsidewallsarevulner-
DAMAGE able,especiallyiftheoutsidesoillevelisashighasthejoists.
SAG Mostoorsaredesignedtocarryliveloadsof30to40poundspersquarefoot(psf).Larger
CONCENTRATED loadscan lead tosaggingandultimately, failure.Specialconsiderationmaybeneededfor
LOADS pianos,waterbeds,aquariums,andoor-to-ceilingbookstorage,forexample.
SAGJOISTS Joists that see concentrated
BELOWWALLS loadsaremorepronetosagging.
Ajoistbelowanon-bearingwall
should be strengthened, often
bydoublingit.Joistsshouldnot
be used below load-bearing
walls. Beams or bearing walls
shouldbeusedhere.
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SAG/HUMP One of the problems often unfairly blamed on joists is caused by an offset bearing
OFFSETBEARING wall. Many houses have a beam or a bearing wall in the basement or crawlspace
WALLS supportingtherstoor.Thereisoftenabearingwallabove,supportingthesecondooror
roofstructure.Ideally,therstoorwallisdirectlyoverthebeamorwallbelow.Ifthewall
isoffsetenough(sometimes12inchesisenough),thejoistswillsagundertherstoor
wallabove.Thiswillleadtoalowspotintheoorwherethewallsitsandahumpinthe
oorabovethebeamorbearingwallbelow.Thissortofmovementisrarelydangerousbutit
doesmakesomepeopleuncomfortable.
5.4.2EngineeredWoodJoists:Engineeredjoistsmayhaveconventionallumbertopandbot-
tomplates,orthetopandbottomplates(anges)maybeLVLs(LaminatedVeneerLumber),
PSLs(ParallelStrandLumber),orLSLs(LaminatedStrandLumber).Websmaybeplywood,
orientedstrandboard(OSB)ormetal.
LVLs,PSLs,andLSLscanalsobeusedasjoists,beams,sills,lintels,columns,studs,rafters,etc.
Glulams(gluelaminatedlumber),madeupofconventionallumberpiecesgluedtogether,can
alsobeusedformanywoodstructuralmembers.
These systemshavemuch longer spans than conventional lumber, andare less prone to
shrinkageandwarpingproblemsthanconventionallumber.Therulesforengineeredwood
aredifferentthanforconventionaljoists,andsomeoftherulesarespecictoindividualman-
ufacturers.Asalways,ahomeinspectionisavisualevaluationofeldperformancerather
thanadesignanalysis.
ProblemsSpecifictoEngineeredWoodJoists
DAMAGE Mechanicaldamageiscommon.Joistsarenotched,drilledandevencutthroughtoaccommo-
dateheating,plumbingandelectricalsystems.Insomecases,joistsarecutaroundstairwells
toimproveheadroom.Holesmaybetoobigorinthewrongplace(manysystemshaveknock-
outsthatindicatewheretheholesmustbe).Split,notchedorcutangesmaybeaproblem.
ThetopandbottomangesofwoodI-joists(asengineeredwoodjoistsareoftencalled)and
trussesarecritical.Anyweakeningwillseriouslyaffectthestrengthofthesystem.
INADEQUATE Inadequateendbearingisaproblem.Moreendbearingthanconventionaljoistsisoften
ENDBEARING required.1-3/4inchesisacommonminimum.
JOISTHANGER Metalhangerscalledjoisthangersareusedwherejoistscannotrestonasupport.Here,the
PROBLEMS joistssitinthehangers,whicharesecuredtothesideofabeamorheader.Joisthangersmay
betooshort,toowide,thewrongtype,andmaynothaveenoughnailsormayhavethewrong
kindofnails.
RIMJOISTISSUES Properrimjoistmaterialmaynotbeused.Engineeredwoodmayrequire3/4-inchplywoodor
specialrimjoistmaterials.Rimsshouldnotbeconventionallumber.Inadequateloadtransfer
throughrimjoistsisacommonproblem.
SQUASHBLOCKS Blocking(squashblocksorwebstiffeners)maybemissingor incompletewherejoistsrest
MISSING/ onbeamsorwhereloadsfrombearingwallsabovearetransmitteddownthroughengineered
INCOMPLETE woodjoiststobeamsorsills.
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BRIDGING Inadequatebridging or load sharing canbe a problem.Different systemshave different
MISSING/ requirementsforbridging.
INEFFECTIVE
5.4.3FloorTrusses:Thetopandbottomhorizontalmembersarecalledchords.Theshorter
interiorpiecesarereferredtoaswebs.Theyaremadefromwood,steeland/orplywood.Trussescanspangreaterdistancesthanconventionalwoodjoists.Beamsandpostsorbear-
ingwallscanbeomittedorremovedwiththeuseofoortrusses.Thesesystemsalsoallow
heating,plumbingandelectricalsystemstorunthroughthetrusses,leavingmoreheadroom
below.Trussesdonotnormallyrequirebridgingorbracing.
Trussesaredeeperthanjoistsandcanrestrictheadroominsomecases.Asageneralguide,
thetrussdepthis1/12to1/20ofitsspan.Mosttrussesare10to18inchesdeep.
CommonProblemswithFloorTrusses
UPSIDEDOWN Many trusseshavea topanda bottom,andmust be installed inthecorrectorientation.Atrussinstalledupsidedownisconsiderablyweakened.
CUT Trussescannotbecutaroundopenings,thewayjoistscan.Conventionaljoistscanbeeldcut
toappropriatelengths.Atrusscannotbecut.Allodd-lengthtrussesmustbeengineered.Site
conditionsthatarenotforeseenorlastminuteplanchanges,canleadtowastedmoneyand
delays,whenworkingwithoortrusses.
SPAN Trussesmaybeoverspannedjustlikejoists.Theseengineeredsystemscanonlybeevaluated
intheeldbytheirperformance.Homeinspectorsdonotreviewthedesignofengineered
systemsliketrusses.
DAMAGE/ROT/ Woodoortrussesarevulnerabletomechanicalabuse,rotandinsects.
INSECTS
5.4.4HeadersandTrimmers:Headersandtrimmersstrengthenanopeningintheoorjoist
patternforastairwellorchimney.Also,basementwindowsoftenpreventoorjoistsfrom
restingonthefoundationwallsandtheseopeningsintheframingpatternmustbestrength-
ened.
Normally,joiststhatcannotrest
onawallorbeamaresecuredto
a header. A header is typically
madeof the samesize lumber
as the joists (e.g. 2x8s). The
header,whichrunsperpendicu-lartothejoists,carriestheload
fromtheshortjoists(tailjoists)
overtotrimmerjoists.Trimmer
joists are the joists on either
sideoftheopeningthatrunfull
length.
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POSTS Postscanbeprovidedatthecornersoftheopeningtocarryloadfromtheheaderdirectly
downtotheoor.Inthiscase,thetrimmerscouldremainsingle.Theheadercanalsobe
supportedwithabearingwallrunningundertheheader.
CommonProblemswithHeadersandTrimmers
UNDERSIZED/ Undersized trimmers and headers are common. It is also common to have the trimmer
NOTCHED notchedatthebottomofthestairwelltoimproveheadroom.This,ofcourse,weakensthe
arrangement.
POOR Theshort(tail)joistsmaybepoorlysecuredtotheheader.Joisthangers(metalbrackets)can
CONNECTION be used to re-secure these tail joists. Headersmay also be inadequately secured to the
trimmers.Again,joisthangerscanbeused.
ROT/INSECT Rotandinsectscanweakenthe
DAMAGE stairwellopeningframing.
5.4.5BridgingandBlocking(andStrapping): Bridging/blocking
preventthejoistsfromtwisting.
Diagonalbridgingisusually2x2
woodblocksormetalstrapping.
Solidblockingisthesamesizeas
the joists. To be effective, the
bridgingorblockingshouldbein
astraightlineandshouldextend
thefulllengthoftheoor.
Solidblockingisrequiredattheendsofjoists.Talljoistsrequire
bridging or blocking at least
everyeight feet.Moreblocking
may be needed where earth-
quakesarearisk.
5.4.6 Cantilevers: Floor joists
maybecantilevered(extended)
slightly beyond their supports.
Acommonexampleisabalcony.
This isoftendone onanupper
oor,wheresupportpostswould
beexpensiveandunsightly.The
principle is that since wood is
relativelystiff,ifpartofajoistis
wellsecuredatoneendandpart
way alongits length, the other
endcanbeunsupported.Rough-
ly1/6ofthejoistspanbetweensupportscanbeusuallybecantileveredsafelybeyondasupport.
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CommonProblemswithCantilevers
OVERSPANNED Wherethejoistsarecantileveredtoofar,thedeckorbalconywillbeweak.Thisisusually
detectablebythespringinessofthestructurewhenwalkingonit.Inseverecases,failureis
possible.Postsorbracescanbeaddedbelowthedeck.
WATER Since the joists penetrate the buildingwall, there is the possibility of leakage into the
PROBLEMS wallsordirectlyintothehomeattheconnectionpoints.Thejointsbetweenthejoistsand
thewallmustbekeptwellsealed.Thisisacommonspotforrottodevelop,attackingboththe
cantileveredjoistsandthewallstructure.
ROT/INSECT Cantileveredwoodstructuresaresusceptibletorotandinsectdamage.
DAMAGE
5.4.7 Steel Floor Framing: Structural framing elements are generally either C-shaped or
U-shapedsteelcomponents.C-shapedelementsaredesignedasload-bearingelements,such
asjoists,whiletheU-shapedpiecesaretracks,orchannels,designedtoholdtheload-bearing
componentsinplace.
Steelframingmembersarenormallyscrewedtogether,althoughtheymayalsobewelded.
Membersmaybescreweddirectlytoeachother,orclips(clipangles)maybeusedtojoin
memberstogether,withtheclipbeingscrewedtobothelements.Screwsarealsousedto
join wood framing, sheathing,
and drywall nished to steel
framing. Securing joists to
steelbeamsrequirestheuseof
clips andpowder-actuatedfas-
tenerguns.
BEARING Bearingstiffeners(webstiffen-
STIFFENERS ers) are requiredwhere a con-
centrated load, suchas a door
jamb,restsonaoorjoist.These
usually take the form of a
sectionofstudortrackmounted
vertically on either sideof the
joistbelowthepointload.Web
stiffeners are also required
wherethejoistrestsonaload
bearingbeamorwall.
HOLES/NOTCHES Steeloorjoistsusuallycomewithpre-punchedholesforplumbingandelectricalwiring,and
shouldbeinstalledsothattheseholesarealignedforeasyinstallationofthemechanicaland
electricalsystems.Thereare industry-speciedrequirementsforotherholes.Joistsshould
notbenotched.
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BRIDGING/ Floorjoistswilltwistandbounceunderloadifthetopsandbottomsarenotproperlybraced.
BLOCKING Thetopistypicallybracedbytheooring.Thebottomscanbebracedwithadrywallceiling
forexample.Wherethereisnoceiling,thejoistbottomsshouldbebracedevery12feet.This
canbeX-bracing,atstrapsalongtheundersidesand/orsolidblocking.
FRAMING Whenthejoistpatternisinterruptedbyopeningsforstairwellsandchimneysforexample,
AROUNDSTAIRS reinforcingwithheadersandtrimmersisrequired,inmuchthesamewayitisdonewithwood
ANDCHIMNEYS framing.
CommonProblemswithSteelFloorFraming
RUST/ Steelframingmembersincontactwithmoistureforaprolongedperiodoftimewillcorrode.
CORROSION Thismaybeanissueinbelow-gradeareasorbelowrooforplumbingleaks.
OVERSPANNED Thespanofasteeloorjoistdependsonitsheight,widthandthegaugeofsteelused.Whilethere
aregeneralguidelines,individualmanufacturershavespecicrequirements.
POOR Weakscrewconnectionscanbeanissuewithsteelframing.
CONNECTIONS
CONTACTWITH Steel reacts with copper plumbing for example, and should not be in contact with
OTHER dissimilar metals. Unless special consideration is given, steel framing should not be
MATERIALS embeddedinconcrete.
DETERIORATION
5.5Sub-ooring(AlsocalledFloorSheathing)
Sub-ooringtransmitstheliveloadsof thepeopleandfurnishingstotheoor joists.Sub-
ooringmaybecoveredwithanishooringmaterialormayserveasanishooringitself.
One-inchthickwoodboardswereusedassub-ooringuntilroughlythe1960s.Morerecently,
plywoodandwaferboardhavebeenused.Thinconcretesuboorsarelesscommon.
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CommonProblemswithSub-flooring
SPRINGYFLOORS Subooringthatistoothinwillbespringyandmayfailunderconcentratedloads(e.g.a
piano).Thisshouldbeoverlaidtoprovideastiffersuboor.
SQUEAKY Subooring not adequately secured to the oor joists may be squeaky. The weight of
FLOORS someonewalkingonaoorwilltemporarilypushthesuboordownontothejoist.When
thefootisremoved,thesuboorwillliftoffslightlyagain.Thenoiseisthenailssqueakingas
theyslideinandout,orpiecesofwoodrubbingagainsteachother.Solutionstothisnuisance
includere-nailing,screwingandgluingthesuboortothejoists.
WATERDAMAGE Waferboardsubooringcanbedamagedbyrelatively smallamountsofwater.Theboard
tendstoswell,resultinginoorunevenness.Theswellingalsopullsthenailsoutofthejoists
orthroughthewaferboard.Ultimately,theboardcanloseitsstrength.
EDGESUPPORT Diagonalplanksubooringmustbesupportedwhereitmeetsthewall.Theendsofsomeof
theplanksmaybeseveralinchesfromaoorjoistandifadequateblockingisnotprovided,the oor will be weak in this
area.Whereplywoodorwafer-
boardsubooringsheetsmeet,
thejointshouldbesupportedby
joists, blocking or tongue-and-
groove connections between
thesheets.
DAMAGE Any subooring can be me-
chanicallydamagedand,unless
repairsaremade,thiscanlead
toan unsafe situation. A com-
monproblemisaholecutfora
heatingregisterthatwasnever
installed. If carpet is laid, this
maynotbenoticeduntilafurni-
turelegisputontheweakspot.
Repairs are, of course, simple
andinexpensive.
UNEVEN Unevensubooringcanbeanuisance.Unevenjoistinstallationisacommoncause,asis
debrisonthetopofthejoistswhenthesuboorislaid.Swollenwaferboardordelaminated
plywoodcanalsoresultinunevenness.Carelessjoiningoftongue-and-groovesheetscanleadtosurfaceirregularity.
ROT/INSECT Subooringissusceptibletorotandinsectdamage.
DAMAGE
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5.6ConcreteFloors
Concreteoorsinhomeswithbasementsareusuallynotstructural.Basementandgarage
oorslabsrestonthegroundandareusuallypouredafterthehouseisbuilt.Modernoors
aretypicallythree-inchthickslabs,althougholdonesmaybeasthinas1/2inch.
Slab-on-gradehomesmayhaveconcreteoorsthatarepartofthestructure.
CommonProblemswithConcreteFloors
CRACKED/ Floorsmaybecrackedorbroken.Replacementisnotapriority,butisoftendonetomakea
BROKEN basementorgaragemoreusable.Brokenutilitylinesareapossibilitywithslabmovementon
slab-on-gradehomes.Themovementmaybesettlementorheavingduetoexpansivesoils,
forexample.
NOSLOPETO Manybasementandgarageslabsdonotslopetodrains.Re-slopingisrarelydonebecauseit
DRAIN isexpensiveandtheproblemofwateronaoorisrarelyserious.
SUSPENDED Suspendedconcreteoorsarenotcommoninhomes.Oneexceptionisconcreteporchslabs
SLABS abovecoldcellars.
Suspendedconcreteoorsabovegradearecommoninhigh-riseandcommercialbuildings,
andusesteelreinforcing.Theyareheavierandmoreexpensivethanconventionalwoodoors,
butcanalsobestrongerandaremorereresistant.Suspendedconcreteoorsystemsarenot
evaluatedduringahomeinspection.
6.0WallSystems
Wallscarrytheweightoftheroofandoorsdowntothefoundations,aswellasprovidingaseparationbetweeninsideandoutside.Wallskeepoutthewind,rain,heat,cold,andnoise,as
wellasprovidinguswithprivacyandsupportforinteriorandexteriornishes.
Afterahomeisbuilt,itmaybedifculttoidentifythewallconstruction.
6.1Materials
6.1.1MasonryWalls:Commonmaterialsincludebrick,stone,concreteblock,cinderblock,
claytileandglassblock.Masonrywallsaretypicallycomprisedoftwofour-inchthickwythes
(layers)of masonry. Theouterwythe isoftenweather-resistantbrickor stone. The inner
wythe(layer)maybelowerqualitybrick,concreteblockorcinderblock.Thefoundationmust
bewideenoughtocarrybothlayersofmasonry.
Mortarusedtobindmasonryunitstogetherisacombinationofcement,sand,andwater.For
moreinformationonbrickandmortar,seeSection3.2intheExteriorchapter.
Themasonryunitsmaybeexposedorcoveredwithstucco,forexample.
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IDENTIFICATION Inmostcases,asolidmasonrywallcanbeidentiedbytheheadercourses(rowswherethe
brickisturnedend-wisetolocktheinnerandouterwythesofthewalltogether).Thisisdone
everyvetosevencourses(rows)upthewall.Sometimeseverybrickinthecourseisturned
end-wise.Often,onlyeveryotherbrickisturned,andsometimesthepatternisrandom.In
mostcases,however,thereareatleastsomeoftheunitsthatareturnedineveryfth,sixth
orseventhcourse.
Metaltiesorspeciallysizedbrickscanalsobeusedtojointheinnerandouterwythes.In
thiscasethewallwillshownoheadercourses,anditwillnotbeapparentthatitisasolid
masonrywall.
Solidmasonrywallshavenotbeencommonlyusedon single-familyhomesinmanyareas
sincetheearly1970s.Areaspronetohurricanesareanexception.
CommonProblemswithMasonryWalls
DETERIORATED Thewallmaybeweakenedifthemasonryorthemortardeteriorates.Thismaybetheresult
ofpoorqualitymasonryormortar,chronicmoistureexposureorfreezing.
CRACKS Cracksinbrickworkmayappearforseveralreasons.Cracksareclues,andtheirsize,location,
directionand rate ofgrowth are all indicatorsofwhat ishappening.Generally speaking,
cracksthroughmortarjointsarelessseriousthancracksthroughthebrickorblock,butthere
areexceptions.
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LEAN/BOW Wheretheinnerandouterwythesarenotadequatelysecuredtogether,theouterwythescan
leanorbowoutwards.Theentirebrickwallmayleanorbowduetofoundationsettlementor
thewallnothavingadequatelateralsupport.Wallsmayalsobepushedoutofplumbby
vehicleimpact,forexample.Ifawallleans,theultimatedangeristhatitmayfall.Themore
immediatedanger,however,isthattheraftersandjoistsrestingonthewallmayslipoffas
thewallmovesoutawayfromthebuilding.Sincetheendsofjoistsmayonlyrestonthewall
byaninchortwo,alittlemovementcancreateanunsafesituation.Ifjoistsorraftersslipoff
theirsupports,theframingsystemwillcollapse.
RAFTERSPREAD Spreadingroofraftersmaypush
thetopofthewallsout,result-
inginanunstablesituation.
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EXCESS Brickcanbecorbelled (offset)
CORBELLING onlyaboutoneinchbeyondthe
brickbelow(i.e.onebrickdoes
nothavetobesetexactlyontop
ofanother).However,thetotal
corbellingmustnotexceedone-
third of the wall thickness to
maintainstability.
6.1.2WoodFrameWalls:Load-
bearingwoodframewallsmay
beinteriororexteriorwalls.
Some stud walls are load-
bearing,othersarenot.Bearing
wallsshouldhaveadoubletop
plate. Non-bearing stud walls
mayhaveonlyasingletopplate.
Asinglesoleplate(alsocalledsillplateorbottomplate)isprovidedineithercase.Noneofthis
isvisibleoncethehomeisnished.
Historically,2x4studshavebeenused,spaced16inchesoncenter,althoughmorerecently,
2x6exteriorwall studs have become common asthey providemorespace for insulation
betweenthestuds.
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CommonProblemswithWoodFrameWalls
Rot, insect attack, mechanical damage, poor quality lumber, poor connections, design
mistakes,poorworkmanshipandexcessivespacingcanallbeproblems.
POORNAILING Inadequatenailing can lead to
ANDOPENING difculties. Openings in walls
maynotbeadequatelyframed.
Wall sections above large
openings for picture windows,
for example, may sag if the
openingsare notbridgedwith
appropriate support headers
(somecalltheselintels).
NOTCHES Holesandnotchescanweaken
ANDHOLES studsiftheyaretoolarge.The
illustrations below provide
someguidelines.
BUCKLING Somewoodstudwallsaresusceptibletobucklingunderloads.Thisisparticularlytrueifthe
wallsarenotbracedwithgirts(blockingbetweenstudsnearthemid-point)orifinterioror
exteriornishesarenotprovided.Ifnishisprovidedononesideofthewall,girtsarenotrequired.
Longerstudsaremoresusceptibletobuckling.Thisiseasytounderstandifyouholdbothends
ofayardstickandtryandpushtheendstowardeachother.Theyardstickbucklesveryeasilyin
themiddle.Thisismoredifcultwithasix-inchrulerofthesamematerial.
Whereanotheroorlevelistobeaddedtoahome,specialconsiderationshouldbegivento
studwalls,whichmaynotbestrongenoughtocarrytheaddedweight.
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CONDENSATION Rotormoldcausedbycondensationinexteriorwallsisaconcern,especiallywhereinsulation
INCOLD isupgradedinolderhouses,andwithouteffectiveair/vaporbarriers.Thiscannotbedetected
CLIMATES duringavisualinspectionanditmaybealongtimebeforethedamageisnoticed.Insome
cases,peelingexteriorpaintsuggeststhatwallcondensationisaproblem.
Thisistypicallyaseasonalproblemincoldclimates,withthecondensationoccurringduringthewintermonthsonly.Warmmoistairentersthewallfromthehouse.Asitpassesthrough,
theaircools.Coolaircannotholdasmuchwatervaporaswarmair.Condensationforms
insidethewallastheaircoolsandgivesoffitswater.
LOWQUALITY Poorqualitystudsorstudsthatwarpandbowcanleadtounevenwallsurfacesinnewhomes.
LUMBER Thebowedortwistedstudshavetoberepairedorreplaced.
GREENLUMBER Buildingwithlumberthatistoowetorgreencanresultinproblemssuchasshrinking,warp-
ing,orbowing.
6.1.2.1BalloonFraming:Balloonframingwascommoninthelate19thandearly20thcentu-
ries. This wood-frame construction technique used conventional studs andoor joists.
However,thewallstudswerecontinuousfromthe
foundationup to theroof line. Theconstruction
process involves setting up the wall studs, and
thenhangingtheoorsystemsfromthem.When
completed,thisresultedinarigidstructure.One
disadvantageisthatarecanmoveveryquickly
upthroughthecontinuousstudspaces.
6.1.2.2 Platorm Framing: Platform or Western
framingisslightlydifferent.Awoodoorjoistand
suboorsystemisprovidedontopofthefounda-
tions.One-storystudwallsarebuiltontheoor.Ifthehouseistwostories,asecondoorplatformis
assembledontopofthestuds,andthenasecond
studwallisbuiltontopofthisplatform.Thiscan
beextendeduptoformathree-storyhouseaswell.
The advantagesof platform framing are ease of
installationandlowermaterialcosts.
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6.1.3SteelFrame:Steelframewallsmaybeload-bearing,carryingtheweightoftheroof
andoorsdowntothefoundations.Theymaybeinteriororexteriorwalls.Steelframewalls
mayalsobeusedasnon-load-bearingpartitionwalls.Whilewoodframingmembershave
traditionally dominated residential construction, the use of lightweight steel framing is
increasing.
StructuralframingelementsaregenerallyeitherC-shapedorU-shaped.C-shapedelements
aredesignedasload-bearingelements,suchasstudsandjoists,whiletheU-shapedpiecesare
tracks,orchannelsthatholdtheload-bearingcomponentsinplace.Insteelconstruction,
tracksreplacethesillsand topplatesusedinwood-frameconstruction.Non-load-bearing
wallsaretypicallythinner,butareotherwisesimilartoload-bearingwalls.
CommonProblemswithSteelFrameWalls
THERMAL Assteelismuchmoreconductivetoheatthanwood,thethermalefciencyofsteel-framed
BRIDGING wallsismuch lessthanthatofawood-framedwall.Steelframedwallsmayhavehalfthe
insulatingvalueofwoodwalls.Thethermalbridgescreatedbysteelstudscanbereduced
throughtheuseofinsulatedsheathingontheoutsideofthestuds,andwiththeuseofwider
studspacing.
CORROSION Someoldersteelframewallsdidnotadequatelydealwiththermalbridgingissues,leadingto
condensationandcorrosionofthesteelstuds.Corrosionmaybeanissuewheneverthereisa
condensationorwaterleakageproblem.
IMPROPER Steel studs usually comewith pre-punchedholesfor plumbingand electricalwiring and
HOLES shouldbeinstalledsothattheseholesarealignedforeasyinstallationofthemechanicaland
electricalsystems.Thereareindustry-speciedrequirementsforotherholes.Improperholes
canweakenthewall.
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REINFORCEMENT Woodnailingstripsareoftenrequiredtoallowdoorjambsandothertrimtobenailedtothe
MISSING/ framing.Finishingscrewsmaybeusedinsteadofnails.Wallshavetobereinforcedinsome
INADEQUATE areas,suchaswhencabinetsaretobesecuredtonon-load-bearingsteelstuds.
6.1.4Brick/StoneVeneer:Abrickorstoneveneerwallhasastructuralwood(ormetal)frame
innerwall,anda four-inchthickmasonryoutersection(veneer),whichdoesnothaveanyload-bearingresponsibility.Typically,metaltiesareusedtosecurethemasonrytothewood
framewall,andtherearenoheadercoursesinthemasonry.Theabsenceofheadersidenties
aveneerwallinmostcases.Mostsolidmasonrywallshaveheaders.
Veneerwallshavebeenthemostcommonmasonrywallsinsingle-familyhomesinmany
partsofAmericasinceabout1970.
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RAINSCREEN Sincetheearly1970s,veneerwallshavehadweepholesprovidedatthebottom.Amodern
PRINCIPLE veneerwallusesarainscreenprinciple.Thisanticipatesthatwinddrivenrainwillpassthrough
amasonrywall,andasaresult,aone-inchairspaceseparatesthemasonryandthewoodstud
wall.Waterrunsdowntheinnerfaceofthebrickortheoutersurfaceofthesheathingand
drainsoutthebottom.
Atthebottomrowofmasonry,everyfourthverticalmortarjoint(typically)isleftopen.A
ashingatthebottomofthewallcavitydirectswateroutthroughtheweepholes.Theash-
ingpreventsthewaterfromenteringthefoundation.Weepholesarealsousedabovedoor
andwindowopenings.
Weepholes also allow pressure balancingon either side of the masonry. The air in the
cavitybehindthemasonryispressurizedaswindblowsagainstthewall,reducingthepressure
differentialacrossthemasonry.Thisreducestheamountofwaterdriventhrough.
Avariationonweepholesisropewicksineveryfourthmortarjointinthebottomrowof
masonry.Whereweepholesorwicksarenoted,thewallismasonryveneer.
CommonProblemswithBrickorStoneVeneerWalls
FOUNDATIONS/ Although the veneer has no load-bearing responsibilities, it must sit on a foundation
CONNECTIONS builttosupporttheweightofthebrickorstone.Ifthefoundationisnotsubstantial,theveneer
wallmaycrackand/orsettleawayfromthewood-framewall.Iftheveneerisinadequately
tiedtothewood-framewall,themasonrymaybulgeorpullaway.Thisisanunsafecondition.
DETERIORATED Deterioratedmasonryormortarcanleadtoseriousproblems.Intheworstcases,theveneerwallhastoberebuilt.Mostbrickisnotdesignedtobeincontactwiththesoil,andshouldbe
keptwellabovegrade.
WEEPHOLES Ifweep holes are lled or omitted, water can collect in the wall cavity, damaging the
sheathingandstuds.
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FLASHING Similar results occur if the
ashingisinappropriateorthe
spacebetweenthemasonryand
sheathingislled.Theashing
cannotnormallybeseenduring
aninspection.
CORBELLING Excessivecorbellingcanmakea
wallunstable.(SeeSection6.1.1)
METALANGLES In some cases, the masonry
veneer is supported on steel
anglesboltedtothefoundation.
Ifthereisanymovementatall,
themasonrymaycrack,bulge,or
pullawayfromthewallbehind.
6.1.5InsulatingConcreteForms(ICFs): Insulating Concrete
Forms(ICFs)areeitherpanelsor
interlocking blocks that are
joinedtogethertocreateform-
work for concrete. The forms
themselves are made out of
insulation, either rigid foam,
suchaspolystyrene,oracombi-
nation of concrete and foam
insulationorwoodchips.Plastic
ties may be used to hold theinnerandouterformstogether.
Oncetheformsareinplace,con-
crete ispoured into theforms,
lling the spaces. Rather than
removetheforms,asinconven-
tional concrete work, they are
leftinplacetoactasinsulation.
ICFwallsarealsousedasfoun-
dationwalls.
Afterahomeisbuilt,itmaybedifculttoidentifythewallcon-
struction.
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INSULATION ICFwallstypicallyprovideatotalR-valueof22,aboutthesameasa2x6studwall.Thesewalls
alsoavoidthermalbridges (areasofhighthermalconductivity)thatarecommoninwood
studwalls.ICFwallsarealsoairtight,whichisgoodforenergyperformance.
REINFORCEMENT ICF walls may include vertical and/or horizontal steel reinforcing bar, especially around
windowanddooropenings.
LEDGERS WhereoorsmeetICFwalls,theymayeitherrestonasillplateonthetopoftheICFwall,or
bearonaledgerboardsecuredtotheICF.
OPENINGS Inmostcases,woodframingisattachedtotheICFatdoorandwindowopeningstoallow
windowframesanddoorjambstobesecured.
ELECTRICAL Electricalwiringandoutletsgenerallyrequiretheinsideformtobe cutaway.Theshallow
WIRING depthoftheformmeansthatwiringmayrequireprotectionfrommechanicaldamage,and
receptaclesneedshallowboxes.
CommonProblemswithICFWalls
WOOD Whilepolystyreneisnotafoodsourceforpests,somewood-destroyinginsectswillnestin,or
DESTROYING travelthrough,thefoam.SomeICFproductscontainchemicalprotection,andsomeICFinstal-
INSECTS lationsusemechanicalbarrierstoprotectagainstinfestation.
RENOVATIONS ItismoredifculttocreateanewopeningoralteranexistingopeninginanICFwallthana
woodframewallbecauseofthepouredconcrete.
6.1.6OtherKindsoWalls
6.1.6.1Log:Modernloghomesutilizepreciselycutlogs,keyedtogether,withgasketsbetween
logs,whileolderlogstructuresaremuchrougher.
SIDINGS Manyolderloghomeswerecoveredwithwoodsheathingsuchasclapboardontheexterior
assoonasthehomeownerscouldaffordit.Stuccowasalsousedontheexteriorinsomecases
andplasterwasoftenappliedontheinterior.Someoldloghomeslookquitedifferentthan
theydidwhentheywerebuilt.Thefoundationsweretypicallystone,andwoodshinglesor
shakeswereoftentheroongmaterial.
CHINKING Chinkingwastraditionallyusedtollthegapsbetweenthelogs.Thiswastypicallyamortar
madeofclay,sandandbinderssuchasanimalhair.Wheregapswerelarge,stoneswould
oftenbettedinbeforethechinkingwasapplied.Duetotheconsiderablemovementdueto
expansionandcontractionoflogsacrossthegrain,chinkingusuallyhadtoberedoneevery
year,atleastinpart.
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CommonProblemswithLogWalls
WOOD Traditionallogconstructiontodayisarelativelyexpensivewaytobuild.Further,woodtends
SHRINKAGE toshrinkandexpandwithchangesinmoisturecontentmuchmoreacrossthegrainthanit
doeswiththegrain.Alogwallgrowsshorterasthewooddriesandtallerwhenthewoodis
wet.Awoodstudwallwillshrinkandexpandmuchlessbecausethewoodgrainisvertical
ratherthanhorizontal.
Ifwoodchangesitsmoisturecontentfrom19%to5%(typicalinahouse),itslengthmay
changeby0.1%alongthegrain,butitswidthmayshrinkby2.5%acrossthegrain.Thismeans
aneight-footlongstudmayonlyshrink1/10inch,whileastackoflogseightfeethighmay
shrinkby2-1/2inches.Thiscanbeasignicantproblemwithwindows,doorsandotherbuild-
ingcomponentsattachedtoalogwall.
CHINKING Regularmaintenanceis required in chinking thegapsbetween thelogs intraditionallog
homes.Themodernmaterialsnowavailableperformmuchbetter.
ROT/INSECT Rotisacommonproblemwithlogsatthebottomofthewall(wheretheymayhavebeenin
DAMAGE contactwithearth)onoldhomes.Thisisnotlikelytobeaproblemwithmodernloghouses
builtonconventionalmodernfoundations.Loghomesaresusceptibletoinsectdamage,of
course.
CONCEALED Wherethelogshavebeencoveredwithsiding,concealedwaterdamageispossible.
DAMAGE
6.1.6.2Post andBeam:This typeof construction,withwoodmembersmuchlarger than
conventionalwood-frameconstruction,isnotcommon,althoughitcanbefoundonolder
countrypropertiesandwascommonlyutilizedforbarns,mills,churchesandotherlargebuild-
ings.Thereareprefabricatedkitsavailable.Othernamesforthistypeofconstructionincludetimber,heavytimberorsemi-millconstruction.
Thisbuildingstyleusesasmallnumberoflargewoodbeamsandposts.Thisisverydifferent
fromconventionalframingthatusesalargenumberofsmallerwoodstudsandjoiststocarry
theloadsdowntothefoundations.
Traditionally,theheavypostsandbeamsweresolidwood.Inhomesbuilttoday,builtupor
glue-laminatedbeamsandpostsarealsoused.Intheoriginalversions,theheavywoodposts
wereoftenaredoutatthetoptoincreasestrength.Afeatureofthesehomeswastheway
thewoodsectionswereconnected.Verysophisticatedmortiseandtenonconnectionswere
utilized,asweredovetailjoints.Manyofthehomeswereassembledwithoutnails,wood
dowelsoftenbeingusedintheirplace.
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The walls were often 2-inch thick planks, installed horizontally or vertically. In some
casesthesewereloadbearing,althoughforthemostparttheysimplyprovidedaweather
tightskin.
Thesehouseswereexpensivetobuildbothintermsofmaterialsandlabor.Largepiecesof
goodqualitylumberhavebecomehardertoobtain.Becausethewoodcomponentswereveryheavy,andsophisticatedjointconnectionswereused,constructionwaslaborintensive.
CommonProblemswithPostandBeamWalls
LACKOF Since the skeleton consisted of a few large components and relatively few connections,
RIGIDITY rigiditycouldbea problem,particularlywherethesheathingdidnotperformastabilizing
function.Becauseoftheintricacyofsomeoftheconnections,therewasagooddealofroom
forerror,andapoorunderstandingofloadtransmissionscouldleadtoconnectionfailures.
EXPANSION/ Theverylargetimbersundergosignicantdimensionalchangeswithchangesinmoisture
CONTRACTION content.Thesebuildingsarenotstatic,expandingandcontractingwithchangesinhumid-ity.Astimbersdriedout,checkingoftendeveloped.Checksarelongitudinalcracks,parallel
tothegrainthatwidenastheygetfurtherfromtheheartwood.Inmanycases,thisisnota
structuralconcern,althoughalargecheckrunninghorizontallythroughabeamdoesreduce
itsloadcarryingcapacity.Wherecontinuouscheckinginapostcouldleadtobuckling,steel
clampsareprovidedaroundtheposts.
FOUNDATION Becauseoftheskeletalnatureoftheframing,largeconcentratedloadswerecarriedtothe
ground.Foundationsystemswereoftentooweakinareasofconcentratedloads,andmuch
strongerthantheyhadtobeinotherareas.
CONNECTIONS Thesebuildingsrelyonrelativelyfewconnections.Poorlymadeconnectionsordamagebyrot
orinsectscanbemoreseriousthanonframeconstruction. SPECIALIZED Sincethistypeofconstructionisspecialized,andnotseenfrequently,localauthoritiesand
INSPECTION professional home inspectorsmay not be familiar with it. In some cases, a specialist is
engagedtocommentonpostandbeamstructures.
REPAIR Repairorreplacementofcomponentsofpostandbeamconstructionisoftendifcultwithout
compromisingtheaestheticorarchitecturalappealofthehome.Thestrengthofstructural
componentsmustbedemonstratedusingengineeringcalculations,ratherthantables.
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6.1.6.3Panelized:Panelizeddescribesamethodofconstruction,ratherthanaspecicsystem.
Intraditionalframing,theindividualcomponentsofthehouse,suchasstuds,joistsandrafters,
arebroughttothesiteandthehouseisbuiltfromindividualpieces.Inpanelizedconstruction,
largepanelsarebuiltoff-site,thenassembledon-siteandsecuredtothefoundation.These
panelsmaymakeuptheoors,walls,ceilingsandroofsofthehome.
Therearevaryingdegreesofpanelization.Panelsmaybesimplestructuralsections,orthey
may include siding, insulation, wiring and even interior nishes. Panelized construction
mayutilizewood framing,steel framing,or a combination of the two. The panels often
includeupgradedinsulationtreatmentandlessthermalbridgingthanfoundinconventional
construction.
Oncethehomeisconstructed,thereisgenerallyverylittledifferencebetweena site-built
homeandapanelizedhome,althoughmanufacturersmaintainthatthebetterworkingenvi-
ronmentandqualitycontrolpossibleinafactory,resultsinbetterbuilthomes.
6.1.6.4StructuralInsulatedPanels(SIP):StructuralInsulatedPanels(SIPs)areonetypeof
panelizedconstruction.SIPsincludethestructuralmember,insulation,airbarrierandexteriorsheathing.Thesetypesofpanelsaresometimescalledstress-skinpanelsbecausethewood
outerlayersactliketheangesofasteelI-beam.Theinsulationactsastheweb.Weendup
withastrongstructuralmemberwithoutusingalotofmaterial.
StructuralInsulatedPanelsaretypically31/2to51/2inchesofexpandedpolystyreneinsula-
tionsandwichedbetween4-footby8-footplywoodororientedstrandboard(OSB)panels.
Theinsulationistypically11/2inchessmallerthantheskinatthetopandbottom,sothe
panelscanreceivesillplatesandtopplates.Somepanelshaverecessesintheinsulationat
thesidestoacceptplywoodorOSBpiecestojoinadjacentpanels.
ELECTRICAL Manypanelsincludehollowchasesintheinsulationtoaccommodateelectricalwiring.Foam
WIRING hastoberemovedtomakeroomforelectricalboxes.
OTHER Similarproductsarealsomade,replacingthewoodwithsteel,aluminum,concreteandber-
MATERIALS glass.Insulationmaterialsaremostoftenexpandedpolystyrene,butcanbepolyurethaneor
othermaterials.
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CommonProblemswithPanelizedWalls
Rot, insect attack, mechanical damage, re damage can all be problems with wooden
components.
WOOD Whilepolystyreneisnotafoodsourceforpests,somewood-destroyinginsectswillnestin,
DESTROYING ortravelthrough,thefoam.SomeSIPproductscontainchemicalprotection,andsomeSIP
INSECTS installationsusemechanicalbarrierstoprotectagainstinfestation.
6.1.6.5RammedEarth:Asthenamewouldsuggestearth,orsoil,istheprimarycomponent
ofarammedearthwall.Nativesoilcansometimesbeused,butascreenedengineeredsoilis
mostoftenused.Idealsoilsareaboutthreepartssandtoonepartclay.
Forms are constructedon conventional foundations.Theformshave plumbing pipes and
electricalconduitplacedpriortopouringthesoil.Athickmixtureofearth,cementandwater
ispouredintotheformsinlayers(typically8inchesthick).Thereistypicallylessthan5%
cementand5to10%watermixedintothesoil.Eachlayeriscompacted(toaboutveinches),andanotherlayeristhenaddedandcompacted.Pneumatictampersaretypicallyusedto
compactthesoilintheforms.Theprocessisrepeateduntilthewalliscomplete.Analternative
approachusesapumptoshootthemixtureintoone-sidedformswithairpressure.
Whenthe forms areremoved, a rough surface ispresented. This canbeanarchitectural
feature,orthewallscanbecoveredwithplasterontheinteriorandstuccoontheexterior.
Finishedwallsaretypically12to18inchesthick.
CommonProblemswithRammedEarthWalls
POOR Rammedearthhomesarelesspracticalinnorthernclimateswherethethermalmassofthe
INSULATION wallsdoesnotprovidegoodinsulatingperformance.Theinsulatingvalueofan18-inchthick
wallmaybeR-4orR-5,wellbelowmodernstandardsincoldclimates.
MOISTURE Likemany building systems, moisture is the enemy.While rammed earthwalls are not
damagedbyoccasionalmoisture,durabilitymaybeanissueinwetclimates.Sometypesof
soilarealsomoremoisture-resistantthanothers.Exteriorsealantsareusedinsomecasesto
protecttheearthwallsfrommoisture.Largeroofoverhangsandraisedfoundationshelpkeep
thewallsdry.
DAMAGE Mechanicalormoisturedamagemayresultinmissingorloosesectionsofthewallcoveringor
thewallitself.Areasclosetogrademaybemorevulnerable.
WINDOWSILLS Windowsmaybeinstalledclosetotheinteriororexteriorwallface.Fromaperformancestandpoint,windowsclosetotheexteriorsurfacearepreferred,sincethiseliminatesawide
exteriorwindowsillthatwilltrapwater.
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6.1.6.6StrawBale: Strawbalewallscanbe loadbearingstructuralmembers,carryingthe
secondoorandroofloads,orthebalesmayllinbetweenorwraparoundawoodpostand
beamframe.Ineithercase,thebalesprovidetheinsulationaswellasthebaseforinterior
andexteriornishes.
Strawisthestalkofgrainssuchaswheat,barley,rye,oatsandrice.Strawshouldnotbeconfusedwithhay,whichisgrassthatisfoodforhorses!Horseswouldnotappreciatebeing
fedstraw.Strawisgenerallyconsideredawasteby-productof agricultureandanuisance
becauseitisslowtodecompose.
Strawbalesusedforbuildingweigh50to90poundseach.Smallbalesmaybe14inchesby18
inchesby36inches.Thelargestbalesmaybe18inchesby24inchesby48inches.Thewallsare
typically13to24inchesthickplusthethicknessofthenishesontheinsideandoutside.
Balewallssitonconventional foundationsthat,withsomeexceptions,shouldbe aswide
asthebales.Thereisusuallyamoisturebarrierbetweenthetopofthefoundationandthe
rst row ofbales. Vertical steelreinforcing bar (re-bar)projects 12 inches out the top of
thefoundationtosecurethebalestothefoundation.There-baristypically1/2inchdiameterandisplacedinthecenterofthefoundation,everytwofeetalongthewalllength,andwithin
12inchesofallcorners.
Thebalesarestackedlikelargebricksintoawallconguration,andaresometimesconnected
toeachother with steelrebar, orwood orbamboo stakes.Water pipesin the balesare
installedincontinuoussleevestoprotectthebalesfromdamageduetoleakage.
Stuccoov