hrb 3 structure 2012 8.5x10.875 - carson dunlop 76 introduction ... windows in basements are usually...

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ThE homE REfEREnCE Book ©

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INTRODUCTION

1.0 Why Buildings move

gRaVITy What causes structures tomove? – In a word, gravity.Gravityisconstantlyworkingtogetthingsclosertotheground.Strongstructuresresistgravity.

STRUCTURE Therearetwocommonwaysastructuremaygiveintogravity.

FaIlURES a)If it is sitting on somethingthatisnotstrongenough,thegroundbelowitwillfail.Bet-ter to build on bedrock thanquicksand.

b)Ifthestructureitselfisweak,it will not support the loadsimposedonit.Thetotalloadismadeupofthefollowing– Dead load–theweightofthestructureitself,live load–furniture,people,wind,snowandearthquakes.

WIND Windactsintermittentlyonstructures.Windforcescanpush,pullorliftbuildings.Buildingsmustbestrongenoughtoresistthelateralandupliftforcesofwindaswellasthedownwardforceofgravity.Hurricanesandtornadoesareextremewindconditions.Theseoftenresultinmechanicaldamagecausedbyprojectiles.

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 aND EROSION intermittentandvariableandcanpush,pullorliftbuildings.Erosionisaslowerformofearth

movement,butitcanhaveadevastatingeffectonstructuresaswell.

COmpONENT House components may fail because they were poorly built with improper materials, or FaIlURES the materials were poorly assembled. Rot, insects, fire and mechanical damage can cause

well-builtstructurestofail.Rustcanattackmetalcomponents.

COmpRESSION Whatforcesaffectindividualstructuralcomponents?Thetwobasicforcesarecompression aND TENSION andtension.Amaterialisundercompressionwhenitisbeingpushedfrombothends.Amate-

rialisundertensionifitispulledon.Componentsincompressiontendtogetshorteroraresquashed.Componentsundertensiontendtogetlongerorarepulledapart.Manybuildingcomponentsfeelacombinationofcompressionandtension.Some building materials are good in compression, others work well in tension and someperform well in both. A pile of bricks is very good in compression; you can stand on it.However,itisverypoorintension.Achildcanpullthepileapart.Achain,ontheotherhand,isverygoodintension.Youcanpullquitehardonbothendsandnothingwillgive,butthemomentyoutrytopushonit,thechaincollapses.Itisnotverygoodincompression.

ShEaRINg aND Differentmaterialsfailindifferentways.Shearingandbendingarecommonmodesoffailure. BENDINg Shearoccurswhenadjacentfacesofamaterialmoveinoppositedirections.Whenabeam

splits,orabrickcracks,itisbecauseofshear.

Bendingismovementwithoutshearing.Aplankspannedbetweentwochairswillbendifsome-onestandsonit,particularlyiftheystandnearthemiddle.Theupperhalfoftheplankispushedtogetherundercompression;thebottomhalfgetsslightlylongerbecauseitisintension.

Buildingcomponentsthatfailbybendingaresaidtosagorbuckle.Somematerialscanbendasignificantamountwithoutlosingtheirstrength.Brittlematerials,however,donotbendmuch before they break. Ductile materials do. Ceramic tile is brittle, rope is ductile. Someductilematerialsareelastic.Thismeanstheywillgobacktotheiroriginalshapeafterbeingbent.Arubberballiselastic;anailisnot.


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DEFlECTION Deflectionisamildformofbending. If structures deflectjustalittle,peopledonotmind.Building codes stipulate howmuchdeflectionisacceptable.Atypical floor joist, for example,isallowedtodeflect1/360thofitsspan.

maTERIal What makes a good buildingSElECTION material? It should be good at

resisting the forces of tensionand compression. It should becheap, easy to work with, light,long lasting, water, rot and fireresistant,andstableunderdiffer-enttemperatureandhumiditylevels.Noonematerialdoesitall.Thatiswhyhousesaremadeofmanymaterials.Woodisoneofthebettermaterialsforsmallbuildings.Itisrelativelygoodinbothtensionandcompression.Steelisalsogoodinbothtensionandcompression.

Buildingmaterialsarechosenbasedoncost-effectiveness.Thegoalistoassembleastructurethatwillperformwellforassmallacostaspossible.Thiscanleadtosomeverysmallmarginsofsafetyand,ofcourse,somefailures.Asnewmaterialsaredeveloped,theyaretried;insomecases,withgreatsuccess;inothercases,withverypoorresults.

Thestructureisbyfarthemostimportantpartofthehouse.Thesafetyandusabilityoftheentirehomedependsonitsstructuralintegrity.Sincemanystructuralcomponentsareburiedbelowgradeorbehindfinishes,muchofthestructuralinspectionisdonebylookingforevi-denceofmovement.Wherenomovementhasoccurred,imperfectionsmaygoundetected.Newinteriororexteriorfinishesandpatchingworkmayconcealimperfectionsovertheshortterm.Inthesecases,problemswillnotbeidentified.

REpaIRS Structuralrepairscanbeverycostly,andinsomecasestheproblemissoseverethatthebuild-ing is torndown. Inmanycases,astructuralengineershouldbeconsultedbeforemakingrepairs.Anincompleteunderstandingofaproblemmayleadtoincorrectsolutionsandalife-threateningsituation.

ChapTER In this chapter we’ll look at foundation configurations briefly, then discuss the variousORgaNIzaTION structurecomponentsoneatatime,startingwiththefootingsandfinishingwiththeroof.

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2.0 Configuration

Homesmayhaveabasement,acrawlspace,both,orneither.Manyhouseshavepartialbase-mentsand/orpartialcrawlspaces.Theconfigurationisdeterminedbyclimate,cost,regionalbuildingpracticesandrestrictionsimposedbythebuildingsite.Inareaspronetohurricanesandflooding,buildingsmaybebuiltonpostsorstiltstokeepthehomewellabovegrade.

2.1 Basement

DESCRIpTION Where frost footings are required, a trench is needed around the house perimeter for thefootingandfoundationsystem.Sincethisexcavationisnecessary,itisnotmuchmoreexpen-sivetodigabigholeandcreateabasement.Inwarmclimateswherefrostfootingsarenotrequired,basementsarerare.

Thebelow-gradespaceisinexpensivetobuildoncetheholeisdug,andcanbeusedforany-thingfromroughstoragetolivingspace.Basementscommonlycontainthemechanicalandelectricalsystemsandmayincludeaworkroomandlaundry(althoughthelaundryisupstairsinmanymodernhomes).Gameroomsandfamilyroomsareoftenlocatedinbasements,andcompleteapartmentscanalsobebuiltbelowgrade.

Disadvantagesofbasementsincludethesusceptibilitytowaterleakageandlackofnaturallight.Windowsinbasementsareusuallysmallandhighonthewall,sincemostofthewallisunderground.Basementceilingsareoftenlow,andevenifthereisnowaterleakage,theycanbecoolanddamp.

2.2 Crawlspace

DESCRIpTION Whereatrenchisdugforthefoundations,andtheearthunderthehousefloorisnotremoved,acrawlspaceiscreated.Itmayhaveanearthfloor,althoughaconcreteslabismoredesirableforstorageandmoisturecontrol.Manymoderncodescall forcrawlspacestobe36 incheshighwhereaccessmustbegained,althoughmanyoldcrawlspacesareless.Someareentirelyinaccessible.Restrictedaccessmakesinspection,maintenanceandrepairmoredifficultandexpensive.

VENTINg Crawlspacesareoften ignoredfor longperiods.Wheremoisture levelsarehigh,structuraldamage,duetorotandinsectactivity,cangounnoticed.Somebuildingstandardscallforonesquarefootofventingforevery500squarefeetofcrawlspacearea.Thisisrarelyprovided.Wherethecrawlspaceisdry,thismaynotbeaproblem.


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2.3 Slab-on-grade

DESCRIpTION Inthistypeofconstruction,apouredconcretefloorrestsdirectlyontheground.Theconcreteslab is at least three inches thick and may or may not be reinforced with steel bars.Immediately below the slab, a moisture barrier is typically laid over about six inches ofgravel.Inmodernconstruction,insulationisoftenprovidedbelowtheslab.Slabsaretypicallysupportedbyfootingsandfoundations.

Thereareseveraltypesofslab-on-grade construction, includ-ing monolithic slab, supportedslab,andfloatingslab.Amono-lithicslabisaconcretefloorandfoundation all poured as one.Thiscanbethoughtofasafloorslab that is thicker around theedges.

A supported slab is not pouredtogether with the founda-tion, but it does rest on thefoundation. The footings andfoundation wall are installedfirst,witha ledgeat thetopofthe foundation to support theslab. Basement floor slabs areoftensupportedslabs.

Thefloatingslabisentirelyinde-pendentofthefoundation.Thefoundation is poured or builtfirst. The slab is not supportedbyorconnectedtothefounda-tion.Thistypeofslabiscommoningarages.

From an inspection and main-tenance standpoint, slab-on-grade is more restrictive thanhomes with basements orcrawlspaces because none ofthefoundationisaccessible.

supportedbyfootingsandfoundations.

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SySTEmS Basementorcrawlspacefloorsareoftenleftasexposedconcrete.ProblemswithwaterorCONCEalED insectinfestation,forexample,canbepickedupearly.Withslab-on-grade,theconcreteslab

isnormallycoveredbysubflooringandfinishflooring.Problemscangoundetectedforsometime.

Wheretheslabispoorqualityconcrete,toothin,ormissingthereinforcingbar,thefloorispronetocrackingandshifting.Subsurfaceerosioncanalsoresultinslabfailure,ascanareasexcavatedforplumbingorheatingpipes.This leadstobroken,unevenfloorsurfaceswithmorepointsofentryforwaterandinsects.Substantialshiftingcandamagetheplumbing,heatingandelectricservicesburiedinorbelowtheslab.Expansivesoilscanheavetheslab,resultinginsimilarproblems.

3.0 Footings

DESCRIpTION Thefunctionoffootingsistotransmittheweightofthehousetothesoil,withoutallowingthehousetosink.Footingsare locatedbelowthefoundationwalls,orattheperimeterofslabs,andbelowcolumnsorpiers.Thehorizontalsurfaceof thefooting is largerthanthefoundation,sotheloadofthehousecanbespreadoutoverawidearea.Footingsaretypically16to24incheswideandsixinchesto16inchesthick.Incoldclimates,footingscarrythehouseloadsbelowthefrost line.Theheavierthebuildingandtheweakerthesoil,the largerthefootingshouldbe.

Footingsmaybeconcrete,brickorstone.Inmodernconstruction,mostfootingsarepouredconcrete,oftenreinforcedwithsteelbars.

FOOTINg TypES Stripfootings(alsocalledspreadfootings) run continuously be-low foundation walls, typicallyaround the building perimeter.Pad footings (also called spotfootings) are smaller and typi-callysupportcolumnsorpiers.

pIER aND Pier and grade beam construc-gRaDE BEam tioniscommoninareaswithex-

pansivesoils.Concretepiersarepoureddowntoadepthwherethe soils are stable. Gradebeams,whichoftenformfoun-dationwalls,spanbetweenthepiers. These grade beams areoftenreinforcedconcrete.


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CommonProblemswithFootings

When the footings fail, the entire house moves. This is often a very serious problem. It isalmostalwaysexpensive,andsometimesimpossible,tocorrect.Sincethefootingsarelocatedbelowthesoil,theycannotbeseen.Itisoftendifficulttoknowwhytheyhavefailed.

Settlementisthemostcommonformoffailure,althoughheavingiscommonincoldclimatesduetofrostexpandingthesoilbelowfootings.

Sometimes footings fail in onearea, and in most cases thefailure is not uniform, (i.e. thebuilding does not sink straightdown but leans to one side oranother).Often,onepartofthehouse will pull away from therest. This leads to cracking ofinterior and exterior wall sur-faces.

SETTlEmENT – Soils prone to compaction or WEak SOIlS movementdonotsupportfoot-

ingswell.Thisincludesrecentlydisturbedsoil.Forexample,ifanexcavation for a foundation isdug too deep, then backfilled to the correct depth, the disturbed soil under the footing islikelytocompactoverthefirstfewyears,resultinginbuildingsettlement.

SETTlEmENT – This is not common on pro-aBSENCE OF fessionally-built houses, but

FOOTINgS may occur in casual construc-tion as well as on porches andpoorly built additions. Somehomeswerebuiltonmudsills–woodbeamslaidonthegroundwith walls built on top of thebeams. These mud sills are re-placed with a foundation andfooting system as the sills rot,heaveorsettle.

SETTlEmENT – ThesemayerodeorweakensoilUNDERgROUND below the footings, causing

STREamS severebuildingsettlement.Itis,of course, very difficult to locate and trace underground streams. They often flow only atcertaintimesoftheyear.

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SETTlEmENT – Settlement may be the result of poor design, or an additional load that has been added.UNDERSIzED For example, when a second floor is added to a bungalow, the weight may cause the

FOOTINgS footingstosink.Theadditionalweightofamasonrychimneycanalsocauselocalizedfootingfailure.

SETTlEmENT – Thefootingmustbestrongenoughnottobreakapartunderaload,andmustbeabletostandFOOTINg uptocontinuousexposuretodampsoil.

DETERIORaTION

SETTlEmENT – Ifthebasementfloorislowered,thereistheriskthatthefootingswillbebrokenoffontheUNDERmINED insideorwilllosetheirsupport.Evenifexcavationisnotdonebelowthefootingsbutdown

OR CUT tothebottomofthem,thelateralsupportforthefootingmaybelost,andthefootingandFOOTINgS foundationwallmaymoveinward.

SETTlEmENT/ Whenabasementfloorislowered,thefootingsshouldbeunderpinned(loweredand,insomeWall FaIlURE – cases,enlarged).Alternatively,onlythecentralsectionofthebasementshouldbelowered,to

lOWERED avoiddisturbinganyofthesoilnearthefootings.DependinguponhowmuchthebasementBaSEmENT floor is lowered, the required clearance from the footings varies. A soils engineer is often

FlOORS consulted and a concrete curb (also called a bench footing or Dutch wall) may be neededaroundtheinsideedgeofthefootingstoensuretheyarenotcompromised.Buildingsettle-mentandfailureoffoundationwallsarebothriskswhenloweringbasementfloors.

Oneofthedangersinloweringbasementfloorsistheincreasedriskofbasementleakage.Noticeinthefollowingillustrationshowthedrainagetileoutsideisnolongerinthecorrectlocationoncethefloorislowered.Itistoohightobeeffective.

Whenexcavationisdoneontheexterior,(e.g.foranadditionorswimmingpool)thefootingscanbedamagedorunderminedinasimilarfashion.


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SETTlEmENT – HousesbuiltonorclosetoslopesmaybesubjecttofailuresasaresultofsoilmovingdownlOT SlOpE theslope.Thismaybeaslowsteadyprocessorasuddeneventtriggeredbyheavyrainsfor

example.Thiscanbeextremelycostlytocorrect.

SETTlEmENT – Houses built on sloping lots may be more prone to footing and foundation failures. TheCUT aND chancesofbuildingondisturbedsoilareincreasedonlotssuchasthese.EffortsmadetolevelFIll lOTS andterracethelotmayresultin

soil being cut out of the hill toform a level terrace under thebackhalfofthehouse.Thissoilis then used as fill in the adja-cent area where the front halfof the house is to stand. Thedownhillhalfofthehousemaybebuiltonfillthatmaynotbewell compacted or may not beabletostayinplaceandsupportthehouse.

On sloping lots, large lateralearth thrust and hydrostaticpressurecanbebuiltupbythesoilonthehighsideofthehome.Waterrunningdowntheslopeisblockedbythebuildingandaccumulateshere.

Onthedownhillside,thefootingsmaynotbedeepenoughincoldclimates.Frostheavecanresultwherethefootingsarelessthanfourfeetbelowgrade.Thesideofthehousewiththelowergradeoftenhasawalk-outbasement,andchancesofafootingbeingtooshallowaregreatesthere.

SETTlEmENT/ SomeclaysoilsthatexpandandcontractsignificantlywithdifferentmoisturecontentsmayhEaVINg – alsoresultinfailure.Theseexpansivesoilscanheavefloorsandfoundationswhentheyget

ExpaNSIVE SOIlS wet.Whentheydry,theyshrinkandallowthebuildingtodrop.Thisisasignificantcauseofhousestructureproblemsinsomeareas.

Tree roots can affect the moisture content of soils noticeably. Most soils have strengthsthatchangewithdifferentmoisturecontents.Someclaysoilstrengthschangedramatically.Thesearepoorbuildingsoils.Siltsarealsopoorbuildingsoils,inmanycasesmuchweakerthanclay.

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ExpaNSIVE Whereexpansivesoilsarecommon,heavingsoilbelowtheslabcanpushtheslabupwardsSOIlS aND atthecenterorattheperimeter,breakingtheconcreteanddamagingutility lines.WhereSlaB-ON- thesesoilsarecommon,theslabsaresometimespost-tensioned.Thismeanstherearesteel

gRaDE hOmES reinforcing cables laid withintheslabandprojectbeyondtheslab edge. The cables aretightened after the concrete ispoured to strengthen the slab,helpingitresisttheforcesoftheexpansive soils. The slabs aresometimesthickened inplaces,often with beams running inboth directions on the under-sideoftheslab.Thesearecalledribbedfoundations.

The expansive soils below theslabareoftensaturatedduringconstructionbeforepouringtheslabsothesoilswillbeamaxi-mum height when the slab ispoured.

FROST hEaVE – Ifthefootingsandfoundationsarenotdeepenough,thegroundbelowthemmayfreeze.FOOTINgS TOO Frozen ground expands and may pick up all or part of the building. This can do serious

ShallOW damage.

FROST hEaVE – Exteriorbasementstairwellsmaycompromisethefootingsincoldclimates. InordertobeOUTSIDE effective,thefootingsincoldclimatesmustbebelowthefrostlevel.Whenanexteriorbase-

BaSEmENT mentstairwellisadded,thestairwellopeningeffectivelylowerstheexteriorgradelevel,andSTaIRWEll alsolowersthedepthtowhichfrostcanpenetrate.Afterthestairwellisinplace,thefrostcan

goseveralfeetbelowthebottomofthestairwellopening.Thiscanleadtofrostheavingofthefootingsandthefoundations.


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A properly added exterior stairwell will include deepened foundations, or a completelyinsulatedapproach,topreventfrostpenetrationbelowthebuildingfootings.

IDENTIFyINg Duringaninspection,theresultsoffootingfailurecanusuallybeseen.Itis,however,difficultThE pROBlEm toknowwhetherthebuildingisstillmoving,andifso,atwhatrate.Itisoftennecessaryto

monitorthebuildingoveraperiodofmonthsorevenyears,toknowwhethertheproblemwillwarrantrepair.Manyfootingfailuresarenotsevereenoughtowarrantrepairs.

REpaIRS – The usual corrective action isUNDERpINNINg to underpin the footings. This

means digging under the exist-ing footing, and adding a newfooting wider and/or deeperthantheoriginal.Thismayhaveto be done in small sections onstrip footings since one cannotexcavateundertheentirehouseatonetime.Usuallytwotofourfootsectionsaredoneatatime.Thisisveryexpensivework.

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REpaIRS – pIlES Insomecases,wherethesoilsaND hElICal aremovingorarelikelytomove,

aNChORS underpinning is not appropri-ate. Piles driven deep into theground are an alternative, butmay not be cost-effective foran existing building. Helicalanchorsaresometimesscrewedinto the soil to support failedfootings.

4.0 Foundations

4.1 general

DESCRIpTION Foundationstransmittheweightofthehousefromtheabove-gradewallsandfloorsdowntothefootings.Wherethereisabasementorcrawlspace,foundationsalsoresistthelateralpressureofthesoil.Thefoundationactsasaretainingwall inthissense. Incoldclimates,foundationscarrytheweightofthehousebelowthefrostlinetopreventfrostheaving.

Typicalfoundationmaterialsarestone,brick,pouredconcrete,concreteblock,cinderblock,insulatedconcreteforms,claytile,andwood.Mostofthesematerialsbehavesimilarly.Woodfoundationsaretheexception.


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COmmON Foundationsmaybecontinuouswalls(stemwalls),oftenmadeofconcrete,masonryblockFOUNDaTION orinsulatedconcreteforms(ICF).Foundationsmayalsobepierssupportedbypadfootings.

TypES Wherefloodingisarisk,homesmaybebuiltonpiersthatarewellabovegrade.Piersmaybebelowgrade,andmaybeconnectedbygradebeams.

Wheresoilconditionsarepoor,thebuildingmayrestonpilesthataredrivenorturneddownintothegroundtosomedepthtoprovideadequatebearingstrengthtosupportthehome.

Twocommonfoundationarrangementsareillustratedbelow.

CommonProblemswithFoundations

CRaCkS/ Foundationwallsmaycrack,bow,spallorshift.Cracksmaybeduetoshrinkage,settlementorBOWINg/ lateralforces.Somecracksareseriouswhileothersare insignificant.BowingisusuallytheSpallINg resultoflateralforces.Spallingindicatespoorqualitymaterialsorchronicwaterproblems.

Someofthecausesoffoundationdefectsareoutlinedbelow.

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INaDEqUaTE Basement and crawlspace foundations are really retaining walls, holding back the soil laTERal SUppORT outside.Ifthefoundationsdonotprovideenoughlateralsupport,theywilldeflectinwards.

This may be the result of mechanical forces exerted during back-filling; back-filling withfrozensoil(coldclimatesonly);unusualfrostdevelopmentinthesoilimmediatelyoutsidethebuilding (cold climates only); foundation walls that are too thin, too tall or do not haveadequatereinforcement;orthehousefloorsystemdoesnotprovideadequatebracingforthetopofthefoundationwall.Thislastproblemiscommononthehighsidewallonaslopinglot.Bothmasonrywallsandpouredconcretewallscanfailifnotproperlybuilt.

INWaRD Foundationwalls thatmove inwardcanberepairedbytyingthembackfromtheoutside,BOWINg usingtiesandanchors.Alternatively,buttressescanbeprovidedontheinterior.Theseoften

areconcreteorconcreteblockstructuresbuiltagainstthebasementwalls.Steelbeamsaresometimesused.Therearealsomodernstructuralfabricsthatcanbeappliedtostrengthenwalls. Another choice is to build a new foundation wall inside the old. In some cases thefoundationisreplaced.

BOWINg/ Mechanicaldamagecausedwhenbackfillingduringconstructionforexample,cangenerallyCRaCkS – be repaired on a localized basis, although re-excavation is often necessary. Using heavy

mEChaNICal equipmentnexttothehome(tore-paveashareddriveway,forinstance)canalsoexerthighDamagE horizontalloadsandresultinbowingandcrackinginthefoundationsofoneorbothhouses.


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BOWINg/ TheheightofsoiloutsideafoundationmayexertenoughforcetocausethefoundationtoCRaCkS – fail.Conventionalfoundationscantypicallytolerate3feetto71/2feetofsoilheightonthe

hEIghT OF outside.Thestrengthofthefoundationisdeterminedbyitsmaterial–concreteorconcreteBaCkFIll blockforexample,thestrengthoftheconcrete,thethicknessofthewall,whetherthewallis

laterallysupportedatthetop,andwhetherthewallisreinforced.

BOWINg/ Theforceexertedby largetree rootsonthe foundationwall can leadtodeflectionof theCRaCkS – TREE foundations.Somesoiltypesshrinkconsiderablyastheydryout.Ifalargetreedrawswater

ROOTS fromsuchsoilsbelowafooting,thefootingmaydropasthesoilcompacts. In this case, the treedamagesthehousewithoutac-tuallytouchingit.

Intheshortterm,treerootdam-age can be arrested by cuttingdown the tree and leaving theroots in place. Over the longterm,therootsmaybeexpectedtorot,leadingtosoilsettlement,resultant water leakage and,in some cases, building settle-ment.Therootsmayhavetoberemoved.

SpallINg/ Waterpenetrationcandeterioratethemortarinmasonryfoundations,reducingitsstrengthDETERIORaTION 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/orasumpandpump, – gROUND areoftennecessary.Consultantsspecializinginsituationssuchastheseshouldbeengaged. WaTER SeeSection10intheInteriorchapter.

SpallINg/ Low quality concrete subjected to damp soils may deteriorate, losing its strength. This is DETERIORaTION commoninpouredconcretefoundations,builtintheearly1900s.Theinteriororexteriorface – pOOR qUalITy oftheconcretemaycrumble(spall).Reducingmoisturepenetrationwillretardthisaction,but CONCRETE ifthedamagehasprogressedtoapointwherethestructuralintegrityiscompromised,sections

ofthefoundationsmayhavetobecompletelyreplaced.Thisisanexpensiveundertaking.

SpallINg/ Somebricksaredesignedforusebelowgrade,butmanyarenot.Theuseofinappropriatebrick DETERIORaTION willresultinashortenedfoundationlife.Ultimately,thebrickshavetobereplaced. – pOOR qUalITy maSONRy

FOUNDaTIONS Ifthefoundationwallsdonotextendwellabovegradelevel,thewallssittingontopofthem TOO ShORT maybeexposedtodampsoilandrotordeteriorate.Foundationsshouldextendatleastfour

tosixinchesabovegradelevel.

CommonProblemsinColdClimates

FROST hEaVE – In cold climates, if the foundations are too shallow, frost may heave even the best-built TOO ShallOW footingsandfoundations.Onslopedlots,thepossibilityofshallowfoundationsisgreateston

thelowside.Propertieswithbasementwalk-outsareoftenvulnerabletofreezingdamage.

FROST hEaVE – Conventionalcoldclimateconstructionassumesthehousewillbeheated.Anunheatedhouse UNhEaTED may have frost penetrating through the basement floor below the footings, leading to hOUSES heaving.Thereisariskinvolvedinleavingahouseunheated.


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aDFREEzINg Adfreezingisaphenomenon wherebydampsoilontheout-

side of the building actuallyfreezes to the building and asthe soil heaves, it will lift thetoppartofthefoundationwall.Horizontal cracks in founda-tionwallsjustbelowgradearetypical.

4.2 Wood Foundations

DESCRIpTION Preservedwoodfoundationswereintroducedintheearly1960s.Severalthousandunitshavebeeninstalled.Lifeexpectanciesofthebelow-groundwoodareestimatedinthe50to100year range, considerably less than many traditional building foundation materials. Somemanufacturersoffer60yearlimitedwarranties.

Thewoodischemicallytreatedto retard rot. Chemical treat-mentforwoodusedinfounda-tionsismoreintensivethanthattypicallyusedinwoodfordecks,fencing,etc.Thewoodfounda-tions may rest on concrete orwood footings. With woodfoundations, special care mustbe taken to ensure that thefoundation is able to performitsretainingwallfunction(ade-quatelyresistinglateralforces).

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CommonProblemswithWoodFoundations

ROT/INSECT Rotandinsectdamagearethemajorenemiesofwoodfoundations.WoodfoundationsshouldDamagE notbeusedinareaspronetowood-destroyinginsectssuchastermites.

4.3 pile Foundations

DESCRIpTION Pilesaresteel,woodorconcretecolumnsdrivenintothesoil.Theyareusedinweaksoilsandmayextenddownthroughthepoorsoil,toreachasoilwithgoodbearingstrength.Pilesmaydependonfrictionbetweenthesidesofthepileandthesoilfortheirsupport.Theymayalsobepoint bearing at the bottom.The building itself rests onbeamsorwallsthatstraddlethepiles. Piles are expensive andoncethebuildingisup,thereisoften no way to know if pileshave been used and where.Again, thepresenceorabsenceof building settlement is theonlywaytodeterminehowsuc-cessfultheapproachhasbeen.

pIlES aND Insomeareas,garagesaretypicallyconstructedonpiles.ThepilessupportpouredconcretegRaDE BEamS gradebeamsforexample,whichinturn,supportthefloorandwallsystems.Thegaragefloor

isthenpouredontheundisturbedsoil.

4.4 pier Foundations

DESCRIpTION Wherecontinuousfoundationsarenotprovided,individualcolumnsor“piers”maybeusedtosupportabuilding.Thepiersshouldrestonafootingbelowthefrostlineincoldclimatesandtypicallythepiersupportsabeam.Thebeam,inturn,supportsthefloor,wallandroofloads.

Piers are commonly found in houses where there is no basement or a partial basement.A crawlspace often has a pier system supporting the structure above. Porches are alsocommonlysupportedbypiers.


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Piersmaybestone,brick,con-crete block, cinder block, orwood. Most of these materi-als behave in a similar fashion.Wood, of course, is the mostvulnerable to rot and insectdamage. As a rule, wood/soilcontactisbestavoided.

Concrete piers are often usedwith grade beams where ex-pansivesoilsareanissue.

CommonProblemswithPiers

SETTlEmENT – Pierproblemsareoftentheresultofinadequatefootings.ThiswillresultinsettlementoftheINaDEqUaTE pierand,ofcourse,thebuildingabove.Ifthepierbaseisnotbelowthefrostlineinnorthern

FOOTINgS climates,frostheavingcanbeaproblem. Inboththesecases,thepiersusuallyhavetoberebuilt.Similarproblemscanresultinareaswithexpansivesoils.

OVERSpaNNED If thepiershavetoogreataspanbetweenthem,thebeamsmaysagortheconcentratedloadsmaycausethepierstosink.Addingpiersisthetypicalsolutionhere.

TOO SlENDER If thepiersaretooslenderorareoutofplumb,theymaynotbecapableofcarryingtheirOR OUT OF intendedloads.Diagonalwoodbracesareusedinsomeareastohelpholdpiersinplace.Piers

plUmB that are deteriorated as a result of moisture or mechanical damage should be repaired orreplacedasnecessary.

Woodpierscanrot,beattackedbywood-boringinsects,fireorbedamagedmechanically.

SkIRTINg Preservedwoodperformsbetterthanmostspeciesofuntreatedwood.Wherepiersareusedinlieuofacontinuousfoundation,thespacebetweenthepiersusuallyhastobefilledintopreventsoilfromfallingintothebasementorcrawlspace.Inabove-gradesituations,skirtingkeepsoutanimalsand,tosomeextent,rain,snowandcold.Skirtingmaybewood,masonryorpouredconcrete,forexample.Wheretheskirtingisnotstructural,repairstodeterioratedskirtingareoftendeferred.Woodskirtingoftendeteriorateswhereitcontactsthesoil.

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5.0 Floors

Floorsprovidethebearingsurfaceforpeopleandfurniture.Theyalsotiethebuildingtogether,addingrigidityandprovidingasurfaceforfloorcoveringsaboveandceilingfinishesbelow.Wewilllookatfloorcomponentsoneatatime.

5.1 Sills

DESCRIpTION Woodsillsprovidealevel,continuouspadbetweenthefoundationtopandthebottomoftheframingsystem.Thesillssecurethefloorsystemtothefoundation.

aNChORED TO Typically,thefloorjoistsrestdirectlyonandaresecuredtothesill.SillsshouldbeanchoredFOUNDaTION tothefoundation.Thisisoftenaccomplishedusingboltsanchoredintothetopofthefounda-

tionwall,passingthroughthesillandsecuredwithawasherandnut.

In new construction, the sill istypicallyawoodframingmem-ber(2x4or2x6)laidflat.Inolderconstruction it may be a sub-stantial wood beam (e.g. 8x8).Wood sills can support woodframing members but shouldnot support brick or stone.

CommonProblemswithSills

CRUShED – Sills may be crushed as a result of concentrated loads. Steel posts built into walls willCONCENTRaTED sometimescausethis.

lOaDS

CRUShED – Ifthebeamsorjoistsaretooshort,andonlytheveryendrestsonthesill(lessthanoneinch,INaDEqUaTE forexample),theconcentratedloadsmaycrushthesill.

END BEaRINg

mOVEmENT – Wherethesillsarenotsecuredtothefoundations,thereisdangerofthebuildingshiftingINaDEqUaTE duringhighwinds,whensignificantupwardsandlateralforcescanbegenerated.

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ROT/INSECT WoodsillsclosetogradelevelaresubjecttorotandinsectattackbecausetheyarewetmuchDamagE ofthetime.Soilistypicallydamp.Sillsmayrotandcrushundertheweightoftheframing

system.Thiswillweakenthestructure,allowingittosettleslightlyandbreaktheconnectionbetweenthefloorandfoundation.

5.2 Beams

DESCRIpTION Beams carry floor and wall loads horizontally to the foundations, walls, columns or posts.Beamsmaybewood(solid,built-uporengineered),plywoodorsteel.

CommonProblemswithBeams

Sag – Undersizedoroverspannedbeamsmaysagorcrack.Thismay leadtofailureof theentireOVERSpaNNED framingsystem.Fortunately,thisrarelyhappens,andalmostneversuddenly.Overspanned

woodbeamscanusuallybeidentifiedreadily,andpostscanbeaddedorthebeamcanbestrengthened.

CRUSh/Fall – Wheretheendbearingisinadequate,thebeamcancrushitselforitssupport.ThereisalsoEND BEaRINg potentialforthebeamtoslipoffitssupport.Typically,threeinchesisconsideredaminimum

endbearingforbeamswhensupportedbymasonryorconcrete.

ROT/INSECT Wood building components are vulnerable to rot, damage, insect attack and fire. Rot andDamagE insectdamagearecommonwherethere iswood/soil contact.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/ RotationofwoodbeamsduetoROTaTION warping or poor support is

relatively uncommon but canlead to damage and ultimatefailure.

NaIlINg aND Built-up wood beams may notBUTT JOINTS beadequatelynailed.Normally,

nailsshouldbeprovidedindou-ble rows every 18 inches alongthebeam.Wherebuttjointsoc-curinwoodbeams,theyshouldbe located over the supportsor as follows: the butt jointsshouldbewithinsixinchesofthequarterpointofthespan.Forexample,ifthespanis12feet,thejointshouldbewithinsixinchesofthethree-footmarkorthenine-footmarkofthespan;(i.e.thejointsshouldbe2-1/2to3-1/2feetfromtheendsupports).

RUST Steel beams are susceptible to rust, particularly if the basement is damp. Steel should bepaintedtopreventrust.Lateralsupportforsteelbeamsistypicallyprovidedbywoodstrap-pingsecuredtothejoists.

laTERal Lateralsupportforsteelbeamsistypicallyprovidedbywoodstrappingsecuredtothejoists.SUppORT Thereareseveralwaystoprovidelateralsupportforwoodbeams.Seetheillustrationbelow.


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SECURINg TO Steelbeamsmaybepoorlysecuredtoposts.WindupliftmaycausethebeamtoliftoffthepOSTS post,orimpactmayshiftitsothatsupportisnolongeroffered.Thebeamandpostshouldbe

bolted,weldedorclippedtogeth-er. In hurricane or earthquakeareas, additional fastening maybe necessary. Special straps areusedtoaccomplishthis.

STRENgTh A visual inspection of a steelbeam cannot determine itsstrengthbecauseitdependsonmorethansize.Theshapeofthebeam,thelengthandthicknessof both the flanges and web,and the weight per linear foot,all influence beam strength.Thecarboncontentofsteelalsoaffectsitsperformance.

STEEl VERSUS Steelbeamscanbemuchstrongerthanwoodbeamsandaremoreresistanttorot,insectandWOOD mechanical damage, but are more expensive, heavier, and more difficult to work with.

Engineeredwoodbeamscanbestrongerthansolidwood,yetarelight,easytoworkwithandlessexpensivethansteel.Woodbeamscanbecutonsitemoreeasilythansteel.Steelbeamsshouldrestonsteelpostsormasonry.Woodbeamscanrestonwoodmembers.

FIRE Fire isaconcernwithbothwoodandsteelbeams. Interestingly,asteelbeamwill lose itsstrengthmuchearlierinafirethanawoodbeam,althoughawoodbeamburnsandasteelbeamdoesnot.Steellosesitsstrengthafterbeingexposedtotemperaturesof1000°F.foraboutfourminutes.Steelbeamssaglikespaghettiduringafire,allowingbuildingstocollapsequickly.Woodburnsbutlosesitsstrengthmuchmoreslowly.

5.3 posts and Columns

DESCRIpTION Posts or columns (two namesfor the same thing) carry theload of the beam verticallydowntothefootings.Theymaybebrick,concreteblock,pouredconcrete,wood,orsteel.

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CommonProblemswithPostsandColumns

SpallINg/ Masonrypostsmaybedeterioratedasaresultofmoistureorpoormortar.Risingdampisa mORTaR common problem with brick columns. This is characterized by deteriorated mortar and DETERIORaTION efflorescence(whitesaltydeposits)onthebottomofthepost.Insomecases,thebrickitself

deteriorates(spalls).

OUT OF plUmB Posts that are out of plumb lose a good deal of their strength. Generally speaking, if thecolumnisoutofplumbbyroughlyone-thirdofitsthickness,theremaybeconcernaboutitsintegrity.

RUST Rustonsteelpostscanbeaconcern.Thisisoftenaseriousproblematthebottomofthepostinachronicallyfloodingbasement.Rustwillquicklyreducetheloadcarryingcapacityofasteelpost.

ROT/INSECT Wood posts are vulnerable to rot and insect attack. This is especially true where the post DamagE penetratesthebasementfloorslab.Correctiveactionoftenincludessimplycuttingoffthe

bottomofthepostandplacingitonaconcretepad.

FOOTINg – A sinking post is usually the result of a missing or inadequately sized footing. Obviously, mISSINg OR TOO suitablefootingsshouldbeprovided.Everypostorcolumnshouldhaveafooting.Thesecan’t Small typicallybeseenoncethehomeisbuilt.

UNDERSIzED OR Columncollapseissomewhatunusualbutisnormallytheresultofanundersizedcolumnor DamagED onethathassufferedmechanicaldamage.

NOT WEll Apostthatisnotwellsecuredtothebeamabovecanallowthehousetoshiftduringwind SECURED TO upliftforces.Thebeamshouldalsobesupportedlaterallytopreventitfrommovingsideways. BEam SeeSection5.2.


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5.4 Floor Joists and Trusses

Thefunctionoftheseframingmembersistocarryandtransferloadsfromthefloorstothefoundations,beamsorbearingwalls.

DESCRIpTION 5.4.1 Conventional Wood Joists:Joistsaretraditionaldimensionallumber,typically2x8,2x10,or2x12.Thesehorizontalmemberscanbe12to24inchesapart,although16inchesisthemostcommon.Theyarelaidonedgesothatthesubflooringisnailedtothetwo-inchside.Floorjoistsshould extend at least 1-1/2inches onto the foundation orbeamateitherend.

JOIST STRENgTh The strength of a joist comeslargelyfromitsdepth.Doublingajoistbyputtinganotherofthesame size beside it will doubleits resistance to bending.Doubling the depth of a joistincreasesitsresistancetobend-ingbyeighttimes!Forexample,the equivalent strength (con-sideringdeflectiononly)oftwo2x10s compared to four 2x8scanbecomparedbymultiplyingthebasetimestheheightcubed.Itisinterestingthattwo2x10saremoreresistanttobendingthanfour2x8s.

Thedeflectionofafloorandjoistsysteminmodernconstructionmaybequitesurprising.Manycodesallowafloortodeflect1/360thofitslengthundernormalloadingifthereisafinishedceilingbelow.Forexample,thefollowingsituationisacceptablebymanycodes:2x10floorjoistsspaced16inchesoncenterspanabout15feet.Whentheroomisoccupiedwithfurnitureandpeople,thecenterpartofthefloorcanbe1/2inchlowerthantheflooredges.Thisiscompletelysafe,andthefloorisnotatriskoffailing.However,thismaynotbesatisfac-torytosomehomeowners.Codesareaminimumstandard.Brittlefloorfinishingmaterialslikeceramictilemaynottolerateaflexlikethis.Morerigidfloorsareoftenusedwheretheflooringmaterialisbrittle.

SpRINgy OR Floors are often bouncy or springy when people walk across a room, but this is notBOUNCy FlOORS necessarilyindicativeofproblems.Lightframingcausesthiscondition,andwhilethefloorcan

bestiffened,thisisrarelydone.

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CommonProblemswithConventionalWoodJoists

OVER SpaNNED Floorjoiststhatareoverspanned(undersized)arepronetosagging.Theacceptablespanofajoistisdeterminedbytheloaditwillcarry,thespeciesandgradeoflumberused,thedepthof the joist, and the spacingbetween joists. Over spanningcanbereadilycorrectedbyadd-ing joists, or adding a beambelow the joists in most cases.The implication of over span-ning is typically a noticeablesag,andinsomecases,abouncyfloorsystem.

DamagE/ Mechanical damage to joists isNOTChED/ common. Joists are commonly

DRIllED notched,drilledandcutthroughtoaccommodateheating,plum-bing and electrical systems. Insomecases,joistsarecutaroundstairwells to improve head-room. Some damage is typical,andthereareseveralguidelinesonacceptablelimits.Joistsaresometimesnotchedattheendtorestonabeamorfoundationwall.Thiscanweakenthejoistconsiderably.Thejoistusuallycrackshorizontallyfromthetopofthenotchtowardsthemid-pointofthespan.

INaDEqUaTE Joistsmaybepronetocrushingattheendsand/orslippingoffthebeamorfoundationwhereEND BEaRINg thereislessthan1-1/2inchofendbearing.


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JOIST haNgER Metalbracketscalled“joisthangers”areusedwherejoistscannotrestonasupport.Here,thepROBlEm joistsarecradledinandnailedtothehangers,whicharesecuredtothesideofabeamor

header.Joisthangersmaybeundersizedorinadequatelynailed.

ROT/ INSECT Rotandinsectscanattackanywoodcomponents.Joistendsclosetooutsidewallsarevulner-DamagE able,especiallyiftheoutsidesoillevelisashighasthejoists.

Sag – Mostfloorsaredesignedtocarryliveloadsof30to40poundspersquarefoot(psf).LargerCONCENTRaTED loads can lead to sagging and ultimately, failure. Special consideration may be neededfor

lOaDS pianos,waterbeds,aquariums,andfloor-to-ceilingbookstorage,forexample.

Sag – JOISTS Joists that see concentratedBElOW WallS loadsaremorepronetosagging.

Ajoistbelowanon-bearingwallshould be strengthened, oftenbydoublingit.Joistsshouldnotbe used below load-bearingwalls. Beams or bearing wallsshouldbeusedhere.

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Sag/hUmp – One of the problems often unfairly blamed on joists is caused by an offset bearing OFFSET BEaRINg wall. Many houses have a beam or a bearing wall in the basement or crawlspace WallS supportingthefirstfloor.Thereisoftenabearingwallabove,supportingthesecondflooror

roofstructure.Ideally,thefirstfloorwallisdirectlyoverthebeamorwallbelow.Ifthewallis offset enough (sometimes 12 inches is enough), the joists will sag under the first floorwallabove.Thiswill leadtoa lowspot inthefloorwherethewallsitsandahumpinthefloorabovethebeamorbearingwallbelow.Thissortofmovementisrarelydangerousbutitdoesmakesomepeopleuncomfortable.

DESCRIpTION 5.4.2 Engineered Wood Joists: Engineeredjoistsmayhaveconventionallumbertopandbot-tomplates,orthetopandbottomplates(flanges)maybeLVLs(LaminatedVeneerLumber),PSLs (Parallel Strand Lumber), or LSLs (Laminated Strand Lumber). Webs may be plywood,orientedstrandboard(OSB)ormetal.

LVLs,PSLs,andLSLscanalsobeusedasjoists,beams,sills,headers(lintels),columns,studs,rafters,etc.Glulams(gluelaminatedlumber),madeupofconventionallumberpiecesgluedtogether,canalsobeusedformanywoodstructuralmembers.

These systems have much longer spans than conventional lumber, and are less prone toshrinkageandwarpingproblemsthanconventionallumber.Therulesforengineeredwoodaredifferentthanforconventionaljoists,andsomeoftherulesarespecifictoindividualman-ufacturers.Asalways,ahomeinspectionisavisualevaluationoffieldperformanceratherthanadesignanalysis.

ProblemsSpecifictoEngineeredWoodJoists

DamagE Mechanicaldamageiscommon.Joistsarenotched,drilledandevencutthroughtoaccommo-dateheating,plumbingandelectricalsystems.Insomecases,joistsarecutaroundstairwellstoimproveheadroom.Holesmaybetoobigorinthewrongplace(manysystemshaveknock-outsthatindicatewheretheholesmustbe).Split,notchedorcutflangesmaybeaproblem.ThetopandbottomflangesofwoodI-joists(asengineeredwoodjoistsareoftencalled)andtrussesarecritical.Anyweakeningwillseriouslyaffectthestrengthofthesystem.

INaDEqUaTE Inadequate end bearing is a problem. More end bearing than conventional joists is often END BEaRINg required.1-3/4inchesisacommonminimum.

JOIST haNgER Metalhangerscalled“joisthangers”areusedwherejoistscannotrestonasupport.Here,the pROBlEmS joistssitinthehangers,whicharesecuredtothesideofabeamorheader.Joisthangersmay

betooshort,toowide,thewrongtype,andmaynothaveenoughnailsormayhavethewrongkindofnails.

RIm JOIST ISSUES Properrimjoistmaterialmaynotbeused.Engineeredwoodmayrequire3/4-inchplywoodorspecialrimjoistmaterials.Rimsshouldnotbeconventionallumber.Inadequateloadtransferthroughrimjoistsisacommonproblem.

SqUaSh BlOCkS Blocking(squashblocksorwebstiffeners)maybemissingor incompletewhere joistsrest mISSINg/ onbeamsorwhereloadsfrombearingwallsabovearetransmitteddownthroughengineered INCOmplETE woodjoiststobeamsorsills.


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BRIDgINg Inadequate bridging or load sharing can be a problem. Different systems have differentmISSINg/ requirementsforbridging.

INEFFECTIVE

DESCRIpTION 5.4.3 Floor Trusses: Thetopandbottomhorizontalmembersarecalled“chords”.Theshorterinteriorpiecesarereferredtoas“webs”.Theyaremadefromwood,steeland/orplywood.Trussescanspangreaterdistancesthanconventionalwoodjoists.Beamsandpostsorbear-ingwallscanbeomittedorremovedwiththeuseoffloortrusses.Thesesystemsalsoallowheating,plumbingandelectricalsystemstorunthroughthetrusses,leavingmoreheadroombelow.Trussesdonotnormallyrequirebridgingorbracing.

Trussesaredeeperthanjoistsandcanrestrictheadroominsomecases.Asageneralguide,thetrussdepthis1/12to1/20ofitsspan.Mosttrussesare10to18inchesdeep.

CommonProblemswithFloorTrusses

UpSIDE DOWN Many trusses have a top and a bottom, and must be installed in the correct orientation.Atrussinstalledupsidedownisconsiderablyweakened.

CUT Trussescannotbecutaroundopenings,thewayjoistscan.Conventionaljoistscanbefieldcuttoappropriatelengths.Atrusscannotbecut.Allodd-lengthtrussesmustbeengineered.Siteconditionsthatarenotforeseenorlastminuteplanchanges,canleadtowastedmoneyanddelays,whenworkingwithfloortrusses.

SpaN Trussesmaybeoverspannedjustlikejoists.Theseengineeredsystemscanonlybeevaluatedinthefieldbytheirperformance.Homeinspectorsdonotreviewthedesignofengineeredsystemsliketrusses.

DamagE/ROT/ Woodfloortrussesarevulnerabletomechanicalabuse,rotandinsects.INSECTS

DESCRIpTION 5.4.4 headers and Trimmers: Headersandtrimmersstrengthenanopeninginthefloorjoistpatternforastairwellorchimney.Also,basementwindowsoftenpreventfloorjoistsfromrestingonthefoundationwallsandtheseopeningsintheframingpatternmustbestrength-ened.

Normally,joiststhatcannotrestonawallorbeamaresecuredtoa header. A header is typicallymade of the same size lumberas the joists (e.g. 2x8s). Theheader,whichrunsperpendicu-lartothejoists,carriestheloadfromtheshortjoists(tailjoists)overtotrimmerjoists.Trimmerjoists are the joists on eithersideoftheopeningthatrunfulllength.

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pOSTS Postscanbeprovidedatthecornersoftheopeningtocarryloadfromtheheaderdirectlydown to the floor. In this case, the trimmers could remain single. The header canalsobesupportedwithabearingwallrunningundertheheader.

CommonProblemswithHeadersandTrimmers

UNDERSIzED/ Undersized trimmers and headers are common. It is also common to have the trimmerNOTChED notchedatthebottomofthestairwelltoimproveheadroom.This,ofcourse,weakensthe

arrangement.

pOOR Theshort(tail)joistsmaybepoorlysecuredtotheheader.Joisthangers(metalbrackets)canCONNECTION be used to re-secure these tail joists. Headers may also be inadequately secured to the

trimmers.Again,joisthangerscanbeused.

ROT/INSECT RotandinsectscanweakentheDamagE stairwellopeningframing.

DESCRIpTION 5.4.5 Bridging and Blocking (and Strapping): Bridging/blockingpreventthejoistsfromtwisting.Diagonalbridging isusually2x2woodblocksormetalstrapping.Solidblockingisthesamesizeasthe joists. To be effective, thebridgingorblockingshouldbeinastraightlineandshouldextendthefulllengthofthefloor.

Solidblockingisrequiredattheends of joists. Tall joists requirebridging or blocking at leastevery eight feet. More blockingmay be needed where earth-quakesarearisk.

DESCRIpTION 5.4.6 Cantilevers: Floor joistsmaybecantilevered (extended)slightly beyond their supports.Acommonexampleisabalcony.This is often done on an upperfloor,wheresupportpostswouldbeexpensiveandunsightly.Theprinciple is that since wood isrelativelystiff,ifpartofajoistiswellsecuredatoneendandpartway along its length, the otherendcanbeunsupported.Roughly1/6ofthejoistspanbetweensupportscanbeusuallybecantileveredsafelybeyondasupport.


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CommonProblemswithCantilevers

OVERSpaNNED Where the joists are cantilevered too far, the deck or balcony will be weak. This is usuallydetectablebythespringinessofthestructurewhenwalkingonit.Inseverecases,failureispossible.Postsorbracescanbeaddedbelowthedeck.

WaTER Since the joists penetrate the building wall, there is the possibility of leakage into thepROBlEmS wallsordirectlyintothehomeattheconnectionpoints.Thejointsbetweenthejoistsand

thewallmustbekeptwellsealed.Thisisacommonspotforrottodevelop,attackingboththecantileveredjoistsandthewallstructure.

ROT/INSECT Cantileveredwoodstructuresaresusceptibletorotandinsectdamage.DamagE

DESCRIpTION 5.4.7 Steel Floor Framing: Structural framing elements are generally either C-shaped orU-shapedsteelcomponents.C-shapedelementsaredesignedasload-bearingelements,suchasjoists,whiletheU-shapedpiecesaretracks,orchannels,designedtoholdtheload-bearingcomponentsinplace.

Steelframingmembersarenormallyscrewedtogether,althoughtheymayalsobewelded.Membersmaybescreweddirectly toeachother,orclips (clipangles)maybeusedto joinmemberstogether,withtheclipbeingscrewedtobothelements.Screwsarealsousedtojoin wood framing, sheathing,and drywall finished to steelframing. Securing joists tosteelbeamsrequirestheuseofclips and powder-actuated fas-tenerguns.

BEaRINg Bearingstiffeners(webstiffen-STIFFENERS ers) are required where a con-

centrated load, such as a doorjamb,restsonafloorjoist.Theseusually take the form of asectionofstudortrackmountedvertically on either side of thejoistbelowthepointload.Webstiffeners are also requiredwhere the joist rests on a loadbearingbeamorwall.

hOlES/NOTChES Steelfloorjoistsusuallycomewithpre-punchedholesforplumbingandelectricalwiring,andshouldbeinstalledsothattheseholesarealignedforeasyinstallationofthemechanicalandelectrical systems.Thereare industry-specified requirements forotherholes. Joistsshouldnotbenotched.

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BRIDgINg/ Floorjoistswilltwistandbounceunderloadifthetopsandbottomsarenotproperlybraced.BlOCkINg Thetopistypicallybracedbytheflooring.Thebottomscanbebracedwithadrywallceiling

forexample.Wherethereisnoceiling,thejoistbottomsshouldbebracedevery12feet.ThiscanbeX-bracing,flatstrapsalongtheundersidesand/orsolidblocking.

FRamINg Whenthejoistpatternisinterruptedbyopeningsforstairwellsandchimneysforexample,aROUND STaIRS reinforcingwithheadersandtrimmersisrequired,inmuchthesamewayitisdonewithwoodaND ChImNEyS framing.

CommonProblemswithSteelFloorFraming

RUST/ Steelframingmembersincontactwithmoistureforaprolongedperiodoftimewillcorrode.CORROSION Thismaybeanissueinbelow-gradeareasorbelowrooforplumbingleaks.

OVERSpaNNED Thespanofasteelfloorjoistdependsonitsheight,widthandthegaugeofsteelused.Whiletherearegeneralguidelines,individualmanufacturershavespecificrequirements.

pOOR Weakscrewconnectionscanbeanissuewithsteelframing.CONNECTIONS

CONTaCT WITh Steel reacts with copper plumbing for example, and should not be in contact withOThER dissimilar metals. Unless special consideration is given, steel framing should not be

maTERIalS – embeddedinconcrete. DETERIORaTION

5.5 Sub-fl ooring (also called Floor Sheathing)

DESCRIpTION Sub-flooringtransmitsthe live loadsofthepeopleandfurnishingstothefloor joists.Sub-flooringmaybecoveredwithafinishflooringmaterialormayserveasafinishflooringitself.

One-inchthickwoodboardswereusedassub-flooringuntilroughlythe1960s.Morerecently,plywoodandwaferboardhavebeenused.Thinconcretesubfloorsarelesscommon.


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CommonProblemswithSub-flooring

SpRINgy FlOORS Subflooring that is too thin will be springy and may fail under concentrated loads (e.g. apiano).Thisshouldbeoverlaidtoprovideastiffersubfloor.

SqUEaky Subflooring not adequately secured to the floor joists may be squeaky. The weight ofFlOORS someonewalkingonafloorwilltemporarilypushthesubfloordownontothejoist.When

thefootisremoved,thesubfloorwillliftoffslightlyagain.Thenoiseisthenailssqueakingastheyslideinandout,orpiecesofwoodrubbingagainsteachother.Solutionstothisnuisanceincludere-nailing,screwingandgluingthesubfloortothejoists.

WaTER DamagE Waferboard subflooring can be damaged by relatively small amounts of water. The boardtendstoswell,resultinginfloorunevenness.Theswellingalsopullsthenailsoutofthejoistsorthroughthewaferboard.Ultimately,theboardcanloseitsstrength.

EDgE SUppORT Diagonalplanksubflooringmustbesupportedwhereitmeetsthewall.Theendsofsomeoftheplanksmaybeseveralinchesfromafloorjoistandifadequateblockingisnotprovided,the floor will be weak in thisarea.Whereplywoodorwafer-boardsubflooringsheetsmeet,thejointshouldbesupportedbyjoists, blocking or tongue-and-groove connections betweenthesheets.

DamagE Any subflooring can be me-chanicallydamagedand,unlessrepairs are made, this can leadto an unsafe situation. A com-monproblemisaholecutforaheatingregisterthatwasneverinstalled. If carpet is laid, thismaynotbenoticeduntilafurni-turelegisputontheweakspot.Repairs are, of course, simpleandinexpensive.

UNEVEN Uneven subflooring can be a nuisance. Uneven joist installation is a common cause, as isdebrisonthetopofthejoistswhenthesubfloorislaid.Swollenwaferboardordelaminatedplywoodcanalsoresultinunevenness.Carelessjoiningoftongue-and-groovesheetscanleadtosurfaceirregularity.

ROT/INSECT Subflooringissusceptibletorotandinsectdamage. DamagE

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5.6 Concrete Floors

DESCRIpTION Concretefloorsinhomeswithbasementsareusuallynotstructural.Basementandgaragefloorslabsrestonthegroundandareusuallypouredafterthehouseisbuilt.Modernfloorsaretypicallythree-inchthickslabs,althougholdonesmaybeasthinas1/2inch.

Slab-on-gradehomesmayhaveconcretefloorsthatarepartofthestructure.

CommonProblemswithConcreteFloors

CRaCkED/ Floorsmaybecrackedorbroken.Replacementisnotapriority,butisoftendonetomakea BROkEN basementorgaragemoreusable.Brokenutilitylinesareapossibilitywithslabmovementon

slab-on-gradehomes.Themovementmaybesettlementorheavingduetoexpansivesoils,forexample.

NO SlOpE TO Manybasementandgarageslabsdonotslopetodrains.Re-slopingisrarelydonebecauseit DRaIN isexpensiveandtheproblemofwateronafloorisrarelyserious.

SUSpENDED Suspendedconcretefloorsarenotcommoninhomes.Oneexceptionisconcreteporchslabs SlaBS abovecoldcellars.

Suspendedconcretefloorsabovegradearecommoninhigh-riseandcommercialbuildings,andusesteelreinforcing.Theyareheavierandmoreexpensivethanconventionalwoodfloors,butcanalsobestrongerandaremorefireresistant.Suspendedconcretefloorsystemsarenotevaluatedduringahomeinspection.

6.0 Wall Systems

Wallscarrytheweightoftheroofandfloorsdowntothefoundations,aswellasprovidingaseparationbetweeninsideandoutside.Wallskeepoutthewind,rain,heat,cold,andnoise,aswellasprovidinguswithprivacyandsupportforinteriorandexteriorfinishes.

Afterahomeisbuilt,itmaybedifficulttoidentifythewallconstruction.

6.1 materials

DESCRIpTION 6.1.1 masonry Walls: Common materials include brick, stone, concrete block, cinder block,claytileandglassblock.Masonrywallsaretypicallycomprisedoftwofour-inchthickwythes(layers) of masonry. The outer wythe is often weather-resistant brick or stone. The innerwythe(layer)maybelowerqualitybrick,concreteblockorcinderblock.Thefoundationmustbewideenoughtocarrybothlayersofmasonry.

Mortarusedtobindmasonryunitstogetherisacombinationofcement,sand,andwater.Formoreinformationonbrickandmortar,seeSection3.2intheExteriorchapter.

Themasonryunitsmaybeexposedorcoveredwithstucco,forexample.


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IDENTIFICaTION Inmostcases,asolidmasonrywallcanbeidentifiedbytheheadercourses(rowswherethebrickisturnedend-wisetolocktheinnerandouterwythesofthewalltogether).Thisisdoneeveryfivetosevencourses(rows)upthewall.Sometimeseverybrickinthecourseisturnedend-wise.Often,onlyeveryotherbrickisturned,andsometimesthepatternisrandom.Inmostcases,however,thereareatleastsomeoftheunitsthatareturnedineveryfifth,sixthorseventhcourse.

Metal tiesorspeciallysizedbrickscanalsobeusedto jointhe innerandouterwythes. Inthiscasethewallwillshownoheadercourses,anditwillnotbeapparentthatitisasolidmasonrywall.

Solidmasonrywallshavenotbeencommonlyusedonsingle-familyhomes inmanyareassincetheearly1970s.Areaspronetohurricanesareanexception.

CommonProblemswithMasonryWalls

DETERIORaTED Thewallmaybeweakenedifthemasonryorthemortardeteriorates.Thismaybetheresultofpoorqualitymasonryormortar,chronicmoistureexposureorfreezing.

CRaCkS Cracksinbrickworkmayappearforseveralreasons.Cracksareclues,andtheirsize,location,direction and rate of growth are all indicators of what is happening. Generally speaking,cracksthroughmortarjointsarelessseriousthancracksthroughthebrickorblock,butthereareexceptions.

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lEaN/BOW Wheretheinnerandouterwythesarenotadequatelysecuredtogether,theouterwythescanleanorbowoutwards.Theentirebrickwallmayleanorbowduetofoundationsettlementorthe wall not having adequate lateral support. Walls may also be pushed out of plumb byvehicleimpact,forexample.Ifawallleans,theultimatedangeristhatitmayfall.Themoreimmediatedanger,however,isthattheraftersandjoistsrestingonthewallmayslipoffasthewallmovesoutawayfromthebuilding.Sincetheendsofjoistsmayonlyrestonthewallbyaninchortwo,alittlemovementcancreateanunsafesituation.Ifjoistsorraftersslipofftheirsupports,theframingsystemwillcollapse.

RaFTER SpREaD Spreadingroofraftersmaypushthetopofthewallsout,result-inginanunstablesituation.


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ExCESS Brickcanbecorbelled (offset)CORBEllINg onlyaboutoneinchbeyondthe

brick below (i.e. one brick doesnothavetobesetexactlyontopofanother).However,thetotalcorbellingmustnotexceedone-third of the wall thickness tomaintainstability.

DESCRIpTION 6.1.2 Wood Frame Walls: Load-bearingwoodframewallsmaybeinteriororexteriorwalls.

Some stud walls are load-bearing,othersarenot.Bearingwallsshouldhaveadoubletopplate. Non-bearing stud wallsmayhaveonlyasingletopplate.Asinglesoleplate(alsocalledsillplateorbottomplate)isprovidedineithercase.Noneofthisisvisibleoncethehomeisfinished.

Historically,2x4studshavebeenused,spaced16inchesoncenter,althoughmorerecently,2x6 exterior wall studs have become common as they provide more space for insulationbetweenthestuds.

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CommonProblemswithWoodFrameWalls

Rot, insect attack, mechanical damage, poor quality lumber, poor connections, designmistakes,poorworkmanshipandexcessivespacingcanallbeproblems.

pOOR NaIlINg Inadequate nailing can lead toaND OpENINg difficulties. Openings in walls

maynotbeadequatelyframed.Wall sections above largeopenings for picture windows,for example, may sag if theopenings are not bridged withappropriate support headers(somecalltheselintels).

NOTChES Holes and notches can weakenaND hOlES studs if they are too large. The

illustrations below providesomeguidelines.

BUCklINg Somewoodstudwallsaresusceptibletobucklingunderloads.Thisisparticularlytrueifthewallsarenotbracedwithgirts(blockingbetweenstudsnearthemid-point)orifinteriororexteriorfinishesarenotprovided.Iffinishisprovidedononesideofthewall,girtsarenotrequired.

Longerstudsaremoresusceptibletobuckling.Thisiseasytounderstandifyouholdbothendsofayardstickandtryandpushtheendstowardeachother.Theyardstickbucklesveryeasilyinthemiddle.Thisismoredifficultwithasix-inchrulerofthesamematerial.

Whereanotherfloorlevelistobeaddedtoahome,specialconsiderationshouldbegiventostudwalls,whichmaynotbestrongenoughtocarrytheaddedweight.


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CONDENSaTION Rotormoldcausedbycondensationinexteriorwallsisaconcern,especiallywhereinsulationIN COlD isupgradedinolderhouses,andwithouteffectiveair/vaporbarriers.Thiscannotbedetected

ClImaTES duringavisualinspectionanditmaybealongtimebeforethedamageisnoticed.Insomecases,peelingexteriorpaintsuggeststhatwallcondensationisaproblem.

Thisistypicallyaseasonalproblemincoldclimates,withthecondensationoccurringduringthewintermonthsonly.Warmmoistairentersthewallfromthehouse.Asitpassesthrough,the air cools. Cool air cannot hold as much water vapor as warm air. Condensation formsinsidethewallastheaircoolsandgivesoffitswater.

lOW qUalITy Poorqualitystudsorstudsthatwarpandbowcanleadtounevenwallsurfacesinnewhomes.lUmBER Thebowedortwistedstudshavetoberepairedorreplaced.

gREEN lUmBER Buildingwithlumberthatistoowetor“green”canresultinproblemssuchasshrinking,warp-ing,orbowing.

DESCRIpTION 6.1.2.1 Balloon Framing: Balloonframingwascommoninthelate19thandearly20thcentu-ries. This wood-frame construction technique used conventional studs and floor joists.However,thewallstudswerecontinuousfromthefoundationuptotheroofline.Thecon-structionprocessinvolvessettingupthewallstuds,andthenhang-ingthefloorsystemsfromthem.Whencompleted,thisresultedina rigid structure. One disadvan-tage is that a fire can move veryquicklyupthroughthecontinuousstudspaces.

DESCRIpTION 6.1.2.2 platform Framing: Plat-formorWesternframingisslightlydifferent. A wood floor joist andsubfloor system is provided ontopofthefoundations.One-storystud walls are built on the floor.If thehouse is twostories,asec-ond floor platform is assembledon top of the studs, and then asecond stud wall is built on topof this platform. This can be ex-tended up to form a three-storyhouse as well. The advantagesof platform framing are ease ofinstallation and lower materialcosts.

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DESCRIpTION 6.1.3 Steel Frame: Steel frame walls may be load-bearing, carrying the weight of the roofandfloorsdowntothefoundations.Theymaybeinteriororexteriorwalls.Steelframewallsmayalsobeusedasnon-load-bearingpartitionwalls.Whilewoodframingmembershavetraditionally dominated residential construction, the use of lightweight steel framing isincreasing.

StructuralframingelementsaregenerallyeitherC-shapedorU-shaped.C-shapedelementsaredesignedasload-bearingelements,suchasstudsandjoists,whiletheU-shapedpiecesaretracks, or channels that hold the load-bearing components in place. In steel construction,tracks replace the sills and top plates used in wood-frame construction. Non-load-bearingwallsaretypicallythinner,butareotherwisesimilartoload-bearingwalls.

CommonProblemswithSteelFrameWalls

ThERmal Assteelismuchmoreconductivetoheatthanwood,thethermalefficiencyofsteel-framedBRIDgINg walls ismuchlessthanthatofawood-framedwall.Steelframedwallsmayhavehalfthe

insulatingvalueofwoodwalls.Thethermalbridgescreatedbysteelstudscanbereducedthroughtheuseofinsulatedsheathingontheoutsideofthestuds,andwiththeuseofwiderstudspacing.

CORROSION Someoldersteelframewallsdidnotadequatelydealwiththermalbridgingissues,leadingtocondensationandcorrosionofthesteelstuds.Corrosionmaybeanissuewheneverthereisacondensationorwaterleakageproblem.

ImpROpER Steel studs usually come with pre-punched holes for plumbing and electrical wiring andhOlES shouldbeinstalledsothattheseholesarealignedforeasyinstallationofthemechanicaland

electricalsystems.Thereareindustry-specifiedrequirementsforotherholes.Improperholescanweakenthewall.


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REINFORCEmENT WoodnailingstripsareoftenrequiredtoallowdoorjambsandothertrimtobenailedtothemISSINg/ framing.Finishingscrewsmaybeusedinsteadofnails.Wallshavetobereinforcedinsome

INaDEqUaTE areas,suchaswhencabinetsaretobesecuredtonon-load-bearingsteelstuds.

DESCRIpTION 6.1.4 Brick/Stone Veneer: Abrickorstoneveneerwallhasastructuralwood(ormetal)frameinnerwall,andafour-inchthickmasonryoutersection(veneer),whichdoesnothaveanyload-bearingresponsibility.Typically,metaltiesareusedtosecurethemasonrytothewoodframewall,andtherearenoheadercoursesinthemasonry.Theabsenceofheadersidentifiesaveneerwallinmostcases.Mostsolidmasonrywallshaveheaders.

Veneerwallshavebeenthemostcommonmasonrywalls insingle-familyhomes inmanypartsofAmericasinceabout1970.

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RaIN SCREEN Sincetheearly1970s,veneerwallshavehadweepholesprovidedatthebottom.AmodernpRINCIplE veneerwallusesarainscreenprinciple.Thisanticipatesthatwinddrivenrainwillpassthrough

amasonrywall,andasaresult,aone-inchairspaceseparatesthemasonryandthewoodstudwall.Waterrunsdowntheinnerfaceofthebrickortheoutersurfaceofthesheathinganddrainsoutthebottom.

Atthebottomrowofmasonry,everyfourthverticalmortarjoint(typically) is leftopen.Aflashingatthebottomofthewallcavitydirectswateroutthroughtheweepholes.Theflash-ingpreventsthewaterfromenteringthefoundation.Weepholesarealsousedabovedoorandwindowopenings.

Weep holes also allow pressure balancing on either side of the masonry. The air in thecavitybehindthemasonryispressurizedaswindblowsagainstthewall,reducingthepressuredifferentialacrossthemasonry.Thisreducestheamountofwaterdriventhrough.

Avariationonweepholes isropewicks ineveryfourthmortar joint inthebottomrowofmasonry.Whereweepholesorwicksarenoted,thewallismasonryveneer.

CommonProblemswithBrickorStoneVeneerWalls

FOUNDaTIONS/ Although the veneer has no load-bearing responsibilities, it must sit on a foundationCONNECTIONS builttosupporttheweightofthebrickorstone.Ifthefoundationisnotsubstantial,theveneer

wallmaycrackand/orsettleawayfromthewood-framewall.Iftheveneerisinadequatelytiedtothewood-framewall,themasonrymaybulgeorpullaway.Thisisanunsafecondition.

DETERIORaTED Deterioratedmasonryormortarcanleadtoseriousproblems.Intheworstcases,theveneerwallhastoberebuilt.Mostbrickisnotdesignedtobeincontactwiththesoil,andshouldbekeptwellabovegrade.

WEEp hOlES If weep holes are filled or omitted, water can collect in the wall cavity, damaging thesheathingandstuds.


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FlaShINg Similar results occur if theflashing is inappropriate or thespacebetweenthemasonryandsheathing is filled. The flashingcannotnormallybeseenduringaninspection.

CORBEllINg Excessivecorbellingcanmakeawallunstable.(SeeSection6.1.1)

mETal aNglES In some cases, the masonryveneer is supported on steelanglesboltedtothefoundation.If there isanymovementatall,themasonrymaycrack,bulge,orpullawayfromthewallbehind.

DESCRIpTION 6.1.5 Insulating Concrete Forms (ICFs): Insulating ConcreteForms(ICFs)areeitherpanelsorinterlocking blocks that arejoinedtogethertocreateform-work for concrete. The formsthemselves are made out ofinsulation, either rigid foam,suchaspolystyrene,oracombi-nation of concrete and foaminsulationorwoodchips.Plasticties may be used to hold theinnerandouterformstogether.Oncetheformsareinplace,con-crete is poured into the forms,filling the spaces. Rather thanremovetheforms,asinconven-tional concrete work, they areleftinplacetoactasinsulation.

ICFwallsarealsousedasfoun-dationwalls.

Afterahomeisbuilt,itmaybedifficulttoidentifythewallcon-struction.

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INSUlaTION ICFwallstypicallyprovideatotalR-valueof22,aboutthesameasa2x6studwall.Thesewallsalsoavoidthermalbridges (areasofhighthermalconductivity) thatarecommon inwoodstudwalls.ICFwallsarealsoairtight,whichisgoodforenergyperformance.

REINFORCEmENT ICF walls may include vertical and/or horizontal steel reinforcing bar, especially aroundwindowanddooropenings.

lEDgERS WherefloorsmeetICFwalls,theymayeitherrestonasillplateonthetopoftheICFwall,orbearonaledgerboardsecuredtotheICF.

OpENINgS Inmostcases,woodframingisattachedtotheICFatdoorandwindowopeningstoallowwindowframesanddoorjambstobesecured.

ElECTRICal Electricalwiringandoutletsgenerallyrequirethe insideformtobecutaway.Theshallow WIRINg depthoftheformmeansthatwiringmayrequireprotectionfrommechanicaldamage,and

receptaclesneedshallowboxes.

CommonProblemswithICFWalls

WOOD Whilepolystyreneisnotafoodsourceforpests,somewood-destroyinginsectswillnestin,or DESTROyINg travelthrough,thefoam.SomeICFproductscontainchemicalprotection,andsomeICFinstal- INSECTS lationsusemechanicalbarrierstoprotectagainstinfestation.

RENOVaTIONS ItismoredifficulttocreateanewopeningoralteranexistingopeninginanICFwallthanawoodframewallbecauseofthepouredconcrete.

6.1.6 Other kinds of Walls

DESCRIpTION 6.1.6.1 log: Modernloghomesutilizepreciselycutlogs,keyedtogether,withgasketsbetweenlogs,whileolderlogstructuresaremuchrougher.

SIDINgS Manyolderloghomeswerecoveredwithwoodsheathingsuchasclapboardontheexteriorassoonasthehomeownerscouldaffordit.Stuccowasalsousedontheexteriorinsomecasesandplasterwasoftenappliedontheinterior.Someoldloghomeslookquitedifferentthantheydidwhentheywerebuilt.Thefoundationsweretypicallystone,andwoodshinglesorshakeswereoftentheroofingmaterial.

ChINkINg Chinkingwastraditionallyusedtofillthegapsbetweenthelogs.Thiswastypicallyamortarmadeofclay,sandandbinderssuchasanimalhair.Wheregapswere large,stoneswouldoftenbefittedinbeforethechinkingwasapplied.Duetotheconsiderablemovementduetoexpansionandcontractionoflogsacrossthegrain,chinkingusuallyhadtoberedoneeveryyear,atleastinpart.


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CommonProblemswithLogWalls

WOOD Traditionallogconstructiontodayisarelativelyexpensivewaytobuild.Further,woodtends ShRINkagE toshrinkandexpandwithchangesinmoisturecontentmuchmoreacrossthegrainthanit

doeswiththegrain.Alogwallgrowsshorterasthewooddriesandtallerwhenthewoodiswet.Awoodstudwallwillshrinkandexpandmuchlessbecausethewoodgrainisverticalratherthanhorizontal.

Ifwoodchanges itsmoisturecontent from19%to5% (typical inahouse), its lengthmaychangeby0.1%alongthegrain,butitswidthmayshrinkby2.5%acrossthegrain.Thismeansaneight-footlongstudmayonlyshrink1/10inch,whileastackoflogseightfeethighmayshrinkby2-1/2inches.Thiscanbeasignificantproblemwithwindows,doorsandotherbuild-ingcomponentsattachedtoalogwall.

ChINkINg Regular maintenance is required in chinking the gaps between the logs in traditional loghomes.Themodernmaterialsnowavailableperformmuchbetter.

ROT/INSECT Rotisacommonproblemwithlogsatthebottomofthewall(wheretheymayhavebeenin DamagE contactwithearth)onoldhomes.Thisisnotlikelytobeaproblemwithmodernloghouses

builtonconventionalmodernfoundations.Loghomesaresusceptibletoinsectdamage,ofcourse.

CONCEalED Wherethelogshavebeencoveredwithsiding,concealedwaterdamageispossible. DamagE

DESCRIpTION 6.1.6.2 post and Beam: This type of construction, with wood members much larger thanconventionalwood-frameconstruction, isnotcommon,althoughitcanbefoundonoldercountrypropertiesandwascommonlyutilizedforbarns,mills,churchesandotherlargebuild-ings.Thereareprefabricatedkitsavailable.Othernamesforthistypeofconstructionincludetimber,heavytimberorsemi-millconstruction.

Thisbuildingstyleusesasmallnumberoflargewoodbeamsandposts.Thisisverydifferentfromconventionalframingthatusesalargenumberofsmallerwoodstudsandjoiststocarrytheloadsdowntothefoundations.

Traditionally,theheavypostsandbeamsweresolidwood.Inhomesbuilttoday,builtuporglue-laminatedbeamsandpostsarealsoused.Intheoriginalversions,theheavywoodpostswereoftenflaredoutatthetoptoincreasestrength.Afeatureofthesehomeswasthewaythewoodsectionswereconnected.Verysophisticatedmortiseandtenonconnectionswereutilized, as were dovetail joints. Many of the homes were assembled without nails, wooddowelsoftenbeingusedintheirplace.

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The walls were often 2-inch thick planks, installed horizontally or vertically. In somecasesthesewereloadbearing,althoughforthemostparttheysimplyprovidedaweathertightskin.

Thesehouseswereexpensivetobuildbothintermsofmaterialsandlabor.Largepiecesofgoodqualitylumberhavebecomehardertoobtain.Becausethewoodcomponentswereveryheavy,andsophisticatedjointconnectionswereused,constructionwaslaborintensive.

CommonProblemswithPostandBeamWalls

laCk OF Since the skeleton consisted of a few large components and relatively few connections, RIgIDITy rigiditycouldbeaproblem,particularlywherethesheathingdidnotperformastabilizing

function.Becauseoftheintricacyofsomeoftheconnections,therewasagooddealofroomforerror,andapoorunderstandingofloadtransmissionscouldleadtoconnectionfailures.

ExpaNSION/ Thevery largetimbersundergosignificantdimensionalchangeswithchanges inmoisture CONTRaCTION content.Thesebuildingsarenotstatic,expandingandcontractingwithchangesinhumid-

ity.Astimbersdriedout,checkingoftendeveloped.Checksarelongitudinalcracks,paralleltothegrainthatwidenastheygetfurtherfromtheheartwood.Inmanycases,thisisnotastructuralconcern,althoughalargecheckrunninghorizontallythroughabeamdoesreduceitsloadcarryingcapacity.Wherecontinuouscheckinginapostcouldleadtobuckling,steelclampsareprovidedaroundtheposts.

FOUNDaTION Becauseoftheskeletalnatureoftheframing,largeconcentratedloadswerecarriedtotheground.Foundationsystemswereoftentooweakinareasofconcentratedloads,andmuchstrongerthantheyhadtobeinotherareas.

CONNECTIONS Thesebuildingsrelyonrelativelyfewconnections.Poorlymadeconnectionsordamagebyrotorinsectscanbemoreseriousthanonframeconstruction.

SpECIalIzED Sincethistypeofconstructionisspecialized,andnotseenfrequently,localauthoritiesand INSpECTION professional home inspectors may not be familiar with it. In some cases, a specialist is

engagedtocommentonpostandbeamstructures.

REpaIR Repairorreplacementofcomponentsofpostandbeamconstructionisoftendifficultwithoutcompromisingtheaestheticorarchitecturalappealofthehome.Thestrengthofstructuralcomponentsmustbedemonstratedusingengineeringcalculations,ratherthantables.


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DESCRIpTION 6.1.6.3 panelized: Panelizeddescribesamethodofconstruction,ratherthanaspecificsys-tem. In traditional framing, the individual components of the house, such as studs, joistsandrafters,arebroughttothesiteandthehouseisbuiltfromindividualpieces.Inpanelizedconstruction,largepanelsarebuiltoff-site,thenassembledon-siteandsecuredtothefoun-dation.Thesepanelsmaymakeupthefloors,walls,ceilingsandroofsofthehome.

Therearevaryingdegreesofpanelization.Panelsmaybesimplestructuralsections,ortheymay include siding, insulation, wiring and even interior finishes. Panelized constructionmay utilize wood framing, steel framing, or a combination of the two. The panels oftenincludeupgradedinsulationtreatmentandlessthermalbridgingthanfoundinconventionalconstruction.

Oncethehomeisconstructed,thereisgenerallyverylittledifferencebetweenasite-builthomeandapanelizedhome,althoughmanufacturersmaintainthatthebetterworkingenvi-ronmentandqualitycontrolpossibleinafactory,resultsinbetterbuilthomes.

DESCRIpTION 6.1.6.4 Structural Insulated panels (SIp): Structural Insulated Panels (SIPs) are one type ofpanelizedconstruction.SIPsincludethestructuralmember,insulation,airbarrierandexteriorsheathing.Thesetypesofpanelsaresometimescalledstress-skinpanelsbecausethewoodouterlayersactliketheflangesofasteelI-beam.Theinsulationactsastheweb.Weendupwithastrongstructuralmemberwithoutusingalotofmaterial.

StructuralInsulatedPanelsaretypically31/2to51/2inchesofexpandedpolystyreneinsula-tionsandwichedbetween4-footby8-footplywoodororientedstrandboard(OSB)panels.The insulation is typically 1 1/2 inchessmaller thantheskinat thetopandbottom,sothepanelscanreceivesillplatesandtopplates.SomepanelshaverecessesintheinsulationatthesidestoacceptplywoodorOSBpiecestojoinadjacentpanels.

ElECTRICal Manypanelsincludehollowchasesintheinsulationtoaccommodateelectricalwiring.Foam WIRINg hastoberemovedtomakeroomforelectricalboxes.

OThER Similarproductsarealsomade,replacingthewoodwithsteel,aluminum,concreteandfiber- maTERIalS glass.Insulationmaterialsaremostoftenexpandedpolystyrene,butcanbepolyurethaneor

othermaterials.

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CommonProblemswithPanelizedWalls

Rot, insect attack, mechanical damage, fire damage can all be problems with woodencomponents.

WOOD Whilepolystyreneisnotafoodsourceforpests,somewood-destroyinginsectswillnestin, DESTROyINg ortravelthrough,thefoam.SomeSIPproductscontainchemicalprotection,andsomeSIP INSECTS installationsusemechanicalbarrierstoprotectagainstinfestation.

DESCRIpTION 6.1.6.5 Rammed Earth: Asthenamewouldsuggestearth,orsoil,istheprimarycomponentofarammedearthwall.Nativesoilcansometimesbeused,butascreenedengineeredsoilismostoftenused.Idealsoilsareaboutthreepartssandtoonepartclay.

Forms are constructed on conventional foundations. The forms have plumbing pipes andelectricalconduitplacedpriortopouringthesoil.Athickmixtureofearth,cementandwateris poured into the forms in layers (typically 8 inches thick). There is typically less than 5%cementand5to10%watermixedintothesoil.Eachlayeriscompacted(toaboutfiveinches),and another layer is then added and compacted. Pneumatic tampers are typically used tocompactthesoilintheforms.Theprocessisrepeateduntilthewalliscomplete.Analternativeapproachusesapumptoshootthemixtureintoone-sidedformswithairpressure.

When the forms are removed, a rough surface is presented. This can be an architecturalfeature,orthewallscanbecoveredwithplasterontheinteriorandstuccoontheexterior.Finishedwallsaretypically12to18inchesthick.

CommonProblemswithRammedEarthWalls

pOOR Rammedearthhomesarelesspracticalinnorthernclimateswherethethermalmassofthe INSUlaTION wallsdoesnotprovidegoodinsulatingperformance.Theinsulatingvalueofan18-inchthick

wallmaybeR-4orR-5,wellbelowmodernstandardsincoldclimates.

mOISTURE Like many building systems, moisture is the enemy. While rammed earth walls are notdamagedbyoccasionalmoisture,durabilitymaybeanissueinwetclimates.Sometypesofsoilarealsomoremoisture-resistantthanothers.Exteriorsealantsareusedinsomecasestoprotecttheearthwallsfrommoisture.Largeroofoverhangsandraisedfoundationshelpkeepthewallsdry.

DamagE Mechanicalormoisturedamagemayresultinmissingorloosesectionsofthewallcoveringorthewallitself.Areasclosetogrademaybemorevulnerable.

WINDOW SIllS Windows may be installed close to the interior or exterior wall face. From a performancestandpoint,windowsclosetotheexteriorsurfacearepreferred,sincethiseliminatesawideexteriorwindowsillthatwilltrapwater.


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DESCRIpTION 6.1.6.6 Straw Bale: Straw bale walls can be load bearing structural members, carrying thesecondfloorandroofloads,orthebalesmayfillinbetweenorwraparoundawoodpostandbeamframe.Ineithercase,thebalesprovidetheinsulationaswellasthebaseforinteriorandexteriorfinishes.

Straw is the stalk of grains such as wheat, barley, rye, oats and rice. Straw should not beconfusedwithhay,whichisgrassthatisfoodforhorses!Horseswouldnotappreciatebeingfed straw. Straw is generally considered a waste by-product of agriculture and a nuisancebecauseitisslowtodecompose.

Strawbalesusedforbuildingweigh50to90poundseach.Smallbalesmaybe14inchesby18inchesby36inches.Thelargestbalesmaybe18inchesby24inchesby48inches.Thewallsaretypically13to24inchesthickplusthethicknessofthefinishesontheinsideandoutside.

Bale walls sit on conventional foundations that, with some exceptions, should be as wideasthebales.Thereisusuallyamoisturebarrierbetweenthetopofthefoundationandthefirst row of bales. Vertical steel reinforcing bar (re-bar) projects 12 inches out the top ofthefoundationtosecurethebalestothefoundation.There-baristypically1/2inchdiameterandisplacedinthecenterofthefoundation,everytwofeetalongthewalllength,andwithin12inchesofallcorners.

Thebalesarestackedlikelargebricksintoawallconfiguration,andaresometimesconnectedto each other with steel rebar, or wood or bamboo stakes. Water pipes in the bales areinstalledincontinuoussleevestoprotectthebalesfromdamageduetoleakage.

Stuccooverwiremeshisthetypicalfinishoutside,anditcanbeusedastheinsidefinishaswell. Limeorclaybasedplastersmaybeapplieddirectly tothe interiorof thestrawbaleswithoutreinforcement.Theinnerplasterandouterstuccofinishesaddstrengthandrigidity,makingthewallastressskinpanel.

STUCCO Exteriorstuccoshouldbreathe.Stuccoswithlimetendtobemorepermeableandallowwallstodrytotheoutside.Otherstuccosarelesspermeableanddonotallowmoisturevaportopassthrough.Thisrestrictsthedryingpotentialofthewall,andmayleadtomoldorrotinthebales.ElastomericstuccoslikeExteriorInsulationandFinishingSystems(EIFS)forexample,arealsoimpermeableanddonotpromotedrying.

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CommonProblemswithStrawBaleWalls

FIRE Firevulnerabilityisroughlythesameasforwoodframewalls.Fireisactuallylessofaproblemwithstrawbalethanwoodframebecauseitishardertoignite.Strawbalewallsdonothavethenaturalchimneysthatoccurinwoodframewalls.However,oncethefireisestablished,strawbalescontributemorefuelthanwoodframeconstruction.Theslower-to-igniteissuemaybemoreimportantforoccupantsafety.

ROT Strawbalewallsarevulnerabletomoistureproblems,likemostotherexteriorwalls.Strawbalehomeswithflatroofsmaybemorepronetofailureduetowaterdamagefromtheroof.Flatroofsoftenaccumulatewater,andaleakingroofmayprovideachronicwatersourceintothewalls.

BElOW gRaDE Strawbalewallsshouldbebuiltwellabovegradeleveltopreventmoisturedamage.Raisedfoundationshelpkeepthebalesdry.Largeroofoverhangsalsohelpkeepthewallsdry.

CRaCkS Cracksinthestuccoandanyopeningsaroundwallpenetrationsarevulnerablepoints.Thegoalistokeepthemoistureoutofthehome.Moisturecontentisusuallylimitedto20%.Somestrawbalehouseshavemoisturemetersbuiltintomonitormoisturelevelsinthebales.

DESCRIpTION 6.1.7 party Walls: Party walls or common walls separate two homes in the same building.Theirmainfunctionistopreventthespreadoffirefromonehometothenext.

maSONRy Masonry party walls provide relatively good fire protection between the two houses, al-thoughtheydon’tblocksoundverywell.

WOOD-FRamE Wood-framepartitionwallsprovidelessfireprotection,althoughtheycanbebetterfromanacousticstandpoint.Somepartywallsaremasonrypartofthewayupthroughthehouse,andwood-frameintheattic.

CommonProblemswithPartyWalls

NONE IN aTTIC Insomeattachedhouses,thereisnowallbetweentheatticareas.Thisspacecanallowfiretospreadquicklyfromonehometoanother.Modernconstructionrulesdonotpermitthisarrangement.

6.2 arches and headers (headers are also called lintels)

DESCRIpTION Archesandheaderstransfertheloadaboveanopeninginamasonrywalltothewallsectionsoneitherside.

lOaDS IN Thearchorheadersupportsatriangularsectionofmasonryabovethearch.TheheightofthemaSONRy WallS triangle is roughly half the width of the opening. This means that a window with twenty

storiesofbrickaboverequiresonlythesamearchasawindowwithsixfeetofbrickabove.


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Thereareseveraltypesofarches.Stone,brickandconcretearethemostcommonmaterialsused.Segmentalarchesarethemostcommon,madeupofseveralpieces.Thearchtypicallyhasariseofatleastoneinchforeachfootofitsspan.

Jack arches have flat tops and bottoms and are often decorative but not functional. Steelheaderstypicallysupportthearch.Thisisnotacommontypeofarch.

Somearcheshavealargermasonryunitatthetop/center.Thisiscalledakeystone,andisoftenthearchitecturalfocusofanarchandwindowsystem.

Headersaretypicallyflat,andusetheinherentstrengthofthematerialtotransmittheload,ratherthanthearchprinciple.Headers(calledlintelsinsomeareas)maybesteel,wood,stoneorconcrete.

Headersaremadeofasinglepiece,wherearchesarebuiltfromseveralpieces.

CommonProblemswithArchesandHeaders

TOO FlaT OR Failureinarchesiscommonwheretheriseisverymodest,orthearchisnotquitewideenoughTOO NaRROW toclearlyspantheopening.Anothercommonproblemwitharches is slightmovementof

thewallsoneitherside.Thisisparticularlycommonwhereawindowordooropeningisclosetotheendofawall.Ononesideofthearch,theremaynotbeenoughmasstoresistthelateralthrustofthearchtransferringitsloadtothewallbeside.Asthethinsectionofwallpushesoutward,thearchdrops.

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DETERIORaTION/ Mortarormasonrydeteriorationcan,ofcourse,leadtofailure.BuildingsettlementmayallowlEaNINg thearchtoopenupanddrop.Anotherproblemisforwardmovementofthearchoutaway

fromthebuilding.Thisisusuallycausedbyfoundationmovementormortarandmasonrydeterioration.Correctiveactionsincluderebuildingthearchoraddingaheader.

UNDERSIzED/ Headersmaybeundersizedfortheload.InadequateendbearingoftheheadersmayleadtopOOR END failure.Steelheaders(lintels)onmasonrywallsshouldextendatleastsixinchesbeyondthe

BEaRINg openingoneitherside.Thiscannotusuallybeseen.

RUST/ROT/ Steel lintelsaresubjecttorust.SpallINg / The rusting steel expands andCRaCkINg may cause horizontal cracks in

themortarjointsatthecornersof the opening. Wood headersare susceptible to rot and in-sectattack.Concreteandstoneheadersaresubjecttocrackingorspalling.

mISSINg Inamateurishconstructionproj-ects,windowsmaybeaddedtomasonry walls or brick veneerwalls with no arch or headerprovided. This will often workin the short term, but prob-lemsusuallydevelopovertime.Missing or inadequate headersshouldbereplaced.

CaUlkINg Steelheaders(lintels)supportingbrickveneershouldhavenocaulkingbetweenthesteelandthebrickabove.Caulkingmaytrapwaterandrustthesteel.


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7.0 Roof Framing

DESCRIpTION Theroofframingisanassemblyofwoodorsteelcomponents.Theroofframingtiesthebuild-ingtogether,addingrigidityandprovidingasurfacefortheroofcovering.Theroofframingalsosupportstheceilingfinishesbelow.Wewill lookattheindividualcomponentsofroofframingsystems.

7.1 Rafters – Wood

DESCRIpTION Rafterscarry the loads fromthe roofsheathing, roofcovering,wind,water, snowand ice.Theseloadsaretransmittedthroughtherafterstobearingwallsorbeamsbelow.Thetermrafterisassociatedwithslopedroofs.Whenthesemembersarefoundonaflatroof,theyarehorizontalandcalledroofjoists,althoughtheydothesamejob.

Rafters can usually be seen overhead when standing in the attic. Some rafters supportfinishedceilings,creatingacathedralceiling.Inthiscase,insulationisoftenfitbetweentherafters.

Woodraftersaretypically2x4s,2x6sor2x8s,spaced16to24inchesoncenter.Conventionalraftershavebeenreplacedbytrusses inmostmodernhomeconstruction.Theengineeredtrussescanspangreaterdistanceslessexpensivelythanconventionalrafters.

When calculating the span of a rafter system, the horizontal span rather than the actuallengthoftherafterisused.Kneewallsorpurlinsmayprovideintermediatesupport,reducingthespan.Collartieshelpkeepraftersinplace.Ceilingjoistsarehorizontalmembersthatoftentiethebottomsofopposingrafterstogether,makingastrongtriangle.

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CommonProblemswithWoodRafters

OVERSpaNNED/ If rafters are overspanned or spaced too far apart, the roof will sag. If rafters are notRaFTER SpREaD adequatelysecuredto thewallsat thebottomedge, the raftersmayspreadapart.This is

commononolderhouses,particularlywithgableroofs.Itisoftennotedattheeaves,becausethesoffitspullawayfromthehousewallastheraftersspread.Inothercases,thespreadingrafterspushthetopofthewalloutward.Thiscanbeveryserious.

Raftersmayalsoseparateattheroofridgeifconnectionsandsupportarepoor.

ROT/INSECT Wood rafters are susceptible to rot, insect, fire and mechanical damage. Rafters mayDamagE/SplIT splitunderload.

CONDENSaTION Attics in cold climates with good insulation but poor ventilation may be susceptible tolEaDS TO ROT condensation problems. Condensation will attack the roof sheathing and the rafters. Left

unchecked,thiscanleadtoroofstructurefailure.Correctiveactionincludesimprovedventila-tionandreplacingdamagedwood.Moldoftendevelopsinatticsasaresultofcondensation.

Sag– Concentrated loads may be a problem around roof dormers. The load from a dormer isCONCENTRaTED transferredtotheraftersoneithersideofthedormer.Unlesstheseraftersarestrengthened,

lOaDS theroofmaysagarounddormers.

In cold climates, roofs mayfail because of a concentratedsnow load. Split-level housesaresusceptibletothisproblem,forexample.Itisnotunusualforsnowdriftstoformonthelowerroof,nearthewallofthehighersection. This leads to big loadsontheraftersortrussesintheseareas.Theraftersmaycrack,sagorspreadatthebottom.Trussesmaycollapse.

7.2 Roof Trusses – Wood

DESCRIpTION Rooftrussesareengineeredassembliesthatperformthesamefunctionasrafters,collarties,kneewalls,purlinsandceilingjoists.Therooftrusscarriestheroofsheathingandshingles,andtheliveloads,transferringtheroofloadstotheoutsideorbearingwalls.Thebottomofthetrussalsosupportstheceilingfinish.

ThereareotherengineeredwoodframingsystemsincludingwoodI-joists,andotherconfigu-rations.Adesignreviewoftheseisbeyondthescopeofahomeinspection.Theperformanceevaluationissimilartotrussesandrafters.


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Most trusses in homes are made of wood. The top and bottom members of the truss arecalledchords.Theinteriormembersofatrussarecalledwebs.Trussmembersarefastenedtogetherwithgussetplates.Thesemaybemadeofplywoodorsteel.Differentconfigurationsoftrusseshavedifferentstrengths,andengineerscanusetheshapeandcomponentsizethatbestsuitsthem.Trussesareengineeredsystems.Trussesarenormallyspaced24inchesapart,butthiscanvary,againdependingonthespansanddepthoftrussdesired.

Therearetwocommontrusstypesusedresidentially.TheFinkor“W”haswebmembersthatforma“W”.TheHowetrusscanbeidentifiedbyverticalwebmembers,includingaverticalwebrunninguptothepeak.Therearemanyvariationsofthesefoundinresidentialconstruc-tion.

Ineithertrusstype,thewebsshouldbeatleast2x4s,unlessspecialengineeringconsiderationhasbeengiven.Wherethecompressionwebsarelongerthansixfeet,theyaresusceptibletobucklingunderheavyloads.Braces,suchas1x4s,shouldbefastenedtothemidpointsofthesewebs.

Where the bottom chord hasa long span between supportpoints, it may not be strongenoughtocarrytheceilingload.If the span is more than tenfeet between support points,thebottomchordshouldbeatleast a 2x5. If the span is morethan 12 feet, the bottom chordshould be a 2x6. Again, specialengineering consideration canresult in deviations from theseguidelines.

CommonProblemswithWoodRoofTrusses

Likeanywoodmember,trussesaresubjecttorot, insectdamage,mechanicaldamageandfire.

CUT Individualchordsorwebsthatarecutordamagedcanbeaseriousproblem.Cuttingatrussinonespotmayseriouslycompromisetheentiretruss.Wheretrussesarecuttoaccommodatechimneysorotherinterruptionsintheroofline,engineeringconsiderationshouldbegiven.

FaSTENINg Trussesmustbewellsecuredtoperformwell.

OVERSpaNNINg Overspanningoftrussescanleadtodeflectionand,inworstcases,roofcollapse.Heavierroofmaterialsuchasconcretetile,orgreatersnowloadsthanexpected,duetounusualconditionsordriftingmaycausetheproblems.Overspanningcannotbeidentifiedduringahomeinspec-tion,butevidenceofdeflectionorfailureisnoted.

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REpaIRS – Reinforcing overspanned or damaged trusses is more difficult than strengthening a rafterDESIgN NEEDED roofsystem.Anengineershoulddesigntherepair.

lONg WEBS – Trusses with web members longer than six feet may be subject to buckling. BracesBRaCINg NEEDED shouldbeaddedtothemidpointsofthewebs.Onebraceattachedtoeachwebwithtwonails

shouldconnectseveralwebsinadjacenttrusses.Thebracesshouldbeatleast1x4s.

INaDEqUaTE UndersizedbottomchordsshouldbestiffenedtopreventceilingsagandcrackingofceilingCEIlINg finishes.Addingasecondmembertothebottomchordwouldnormallybesatisfactory.

SUppORT

TRUSS UplIFT Aphenomenonknownastrussupliftisrelativelycommonincoldclimates.Thetemperatureandhumiditychangesintheatticduringthewintermonthsaffectthesectionsofthetrussabovetheinsulationleveldifferentlythanthebottomchord,whichisburiedintheinsulation.Thisresultsinanupwardbowingofthebottomchord.

Theresultoftrussupliftisthatthecentersectionofthebottomchordmovesup,andgapsaslargeas1-1/2inchesappearatthetopoftheinteriorwalls,wheretheyjointheceiling.Theceilingispickedupbythetruss.Itisalsopossiblethattheinteriorwallbelowwillbeliftedup,andseparationwilloccurbetweenthewallandthefloor.

Acommonsolutionistosecureamoldingtotheceiling(butnottothewall).Astheceilingmovesupanddown,themoldingwillslideupanddownthewall,concealingthegap.

Anothersolutionistodisconnecttheceilingfinishesfromthetrussduringconstructionandtocliptheceilingfinishestothewall.Thisallowstheceilingtobendveryslightly,butnottocrack.

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7.3 Steel Framing

DESCRIpTION Steelroofframingperformsverymuchlikewoodframing.Likewood,steelroofframingmaybemanufacturedtrussesorsite-assembledraftersandjoists.Theprinciplesofwoodframingalsoapplytosteelroofframing,althoughcontinuousbridgingontheraftersisoftenneeded,either on the underside, or through the knockouts. The undersides of joists will twist andmoveunlesstheyarerestrained.

Woodsheathingmaterials,suchasplywood,arescrewedtothesteel roof structure. Roofingmaterialsareinstalledoverthissheathingasnormal.

CommonProblemswithSteelRoofFraming

RUST Steelis,ofcourse,vulnerabletocorrosionwithlong-termexposuretomoisture.

hOlES Anyholesthatarecreatedshouldbeatleast10inchesawayfromtheendoftherafter,posi-tionedinthemiddleoftherafter,andshouldnotbewiderthan1-1/2inchesandnotlongerthanfourinches,unlesstheyarereinforced.

NO DESIgN Steelroofsareengineeredsystems,andaswithwoodtrusses,homeinspectorsdonotassessREVIEW theirdesign.

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7.4 Collar Ties

DESCRIpTION Collartiesmaybeinstalledtopreventraftermovement.Thesearetypicallywoodmembers(atleast1x4s)installedhorizontallyacrosstheatticspace.Theyareconnectedateitherendtoopposingrafters.Insomecircumstances,metalstrapsmaybeusedinsteadofcollartiestopreventuplift.

CommonProblemswithCollarTies

mISSINg, WRONg Missingcollartiescanbeaddedreadily.Collartiesmaybeinstalledincorrectlyorfastened lOCaTION OR poorly. pOOR CONNECTION

BUCklED aND When collar ties are installed to prevent rafter sagging, the compression from opposing BROkEN raftersmaybuckleandcrackthecollarties.Addingbraceswillpreventthis.Brokencollarties

canbereplacedasneeded.

7.5 purlins

DESCRIpTION Purlinspreventraftersag.Thesearewoodcomponentsthesamesizeastherafterstheysup-port.Theyarenailedtotheundersideoftheraftersandaresupported,inturn,by2x4braces,whichextenddown,usuallyonanangleratherthanvertically,toabearingwallbelow.Seeillustrationonnextpage.

CommonProblemswithPurlins

Likeanywoodcomponent,purlinsaresubjecttorot,insectandmechanicaldamage.

STRUTS – mISSINg Bracesorstrutsnomorethanfourfeetapartshouldsupportthepurlins.

STRUTS – SlOpE Strutsshouldbeinstalledwithaslopeofnotlessthan45degreesfromhorizontal.Anylessthanthisandthestrutswillnotproperlytransfertheirload.

STRUTS – Thestrutsthemselvesshouldbebracediftheyarelongerthaneightfeet.Astripoflumber UNBRaCED attachedperpendiculartothestrutswillpreventbuckling.


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7.6 knee Walls

DESCRIpTION Knee walls are intermediatesupports that prevent raftersag. These small walls in theatticaretypicallybuiltwith2x4woodstuds.Theyrunfromtheatticflooruptotheundersideoftheraftersneartheirmid-point.In 1-1/2 or 2-1/2 story houses,knee walls form the walls of aroomontheupperfloor.Theserooms often have a partlyslopedceilingasaresult.

CommonProblemswithKneeWalls

pOORly SECURED/ Ifthekneewallsarenotadequatelysecuredtotheraftersaboveorthejoistsbelow,theywillWEak FlOOR move.Ifthefloorjoistsystembelowisnotstrongenough,orthereisnopartitionbelow,this

canleadtodeflectionanddamageintheceilingbelow.

lOCaTION Ifthekneewallisnotnearthemidspanoftherafters,itmaynotbeeffectiveinpreventingraftersag.

DamagE/ROT/ Likeanywoodcomponent,kneewallsaresubjecttorot,insectandmechanicaldamage. INSECT DamagE

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7.7 Roof Sheathing

DESCRIpTION Sheathingsupportstheroofcovering,transmittingtheloadsfromthecoveringandtheliveloadsduetowater,snowandwindtotherafters,trussesorroofjoists.

Upuntilthe1950s,virtuallyallroofsheathingwaswoodplank.Plywoodroofsheathingin4-footby8-footpanelsbecamepopularinthe1960s,andwaferboardpanelsarrivedinthe1970s.

Plywoodshouldbelaidwiththesurfacegrainperpendiculartotherafters,trussesorjoists.Theeight-footlengthshouldbeacrosstherafterswitheachendsupportedbyarafter.Theotheredgesshouldalsobesupported,typicallybymetal“H”clipslocatedbetweenrafters.Theseclipsnotonlysupporttheedges,butkeepthesheetsslightlyseparatedtoallowforexpansionwithoutbuckling.

Thethicknessofthesheathingisdeterminedbythespacingoftheraftersandtheliveroofloads. Modern construction typically employs trusses or rafters on 24 inch centers andplywoodsheathing3/8inchthick(orwaferboardsheathing7/16inchthick).Thisleadstoafairlyspringyroofsurfacewhenwalkedupon.Unusuallyheavyloadsorslightweakeningoftheplywoodduetohighmoisture levels intheatticcan leadtosaggingof thesheathingbetweenthesupports.Normallythisisnotastructuralflaw,althoughitisunsightly.


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CommonProblemswithRoofSheathing

DamagE/ROT/ Likeanywoodcomponent,roofsheathingissubjecttorot, insectdamageandmechanical INSECT DamagE damage.

DamagE – Condensationinanatticcancauseproblems.Plywoodroofsheathingwillbegintodelaminate CONDENSaTION andwaferboardsheathingwillswell.Thiscancauselossofsheathingstrengthandrender

thenailingineffectiveasnailsarepulledoutoftheraftersorthroughthesheathing.Inseverecases,theroofcoveringhastoberemovedandthesheathingreplaced.

Concealedcondensationincathedralroofsisacommonproblemandconsiderabledamagecanoccurbeforethereareanyvisualclues.

mOlD Mold often appears when there has been condensation in the attic. Once the moisture isremoved,themoldstopsgrowing.Removaloftheinactivemoldisnotnecessary,althoughmanyhomeownersremoveitbecauseofthestigmaattachedtomold.

TOO ThIN Sheathingthatistoothinfortheapplicationwillsagunderload.Aesthetically,thisisoftenunacceptable,althoughsaggingtothepointoffailureisunusual.

Sheathingthicknessisdeterminedinpartbythespacingoftheraftersortrussesbelow.Thick-ersheathingisneededwhenthespansaregreater.Sheathingthicknessisalsodeterminedbytheliveloadsfromwindandsnowaswellasdeadloadsfromroofcoverings.

EDgE SUppORT Unsupported edges of roof sheathing may lead to differential movement between twopanels.Thiscanleadtohorizontalridgesappearingintheroofing.Ifthesheathingisunusu-allythick,edgesupportisnotnecessary.

FIRE RETaRDaNT Fire retardant treated (FRT) plywood was recognized as a problem in the late 1980s. TREaTED (FRT) Delaminationandweakeningofthisplywoodcanleadtoalossofroofshinglesandultimately plyWOOD collapse.Whereithasbeguntofail,itshouldbereplaced.

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8.0 masonry Chimneys

DESCRIpTION Thestructuralfunctionofachimneyistocarryitsownweightdowntothefoundationsandfootingswithoutmoving.(WelookatotherchimneyfunctionsintheRoofingandHeatingchapters.)

CommonProblemswithMasonryChimneys

lEaNINg Chimneysthatleanabovetherooflevelshouldbebracedorrepairedasnecessary,withoutdelay.

FOUNDaTION Localized foundation settle-pROBlEmS ment in a house around the

chimney is fairly common,typically because the founda-tionswerenotlargeenoughtocarrytheweightofthemason-ry.Thechimneymayeventuallyfall over, but the problem canbecomeveryseriousbeforethispoint.Achimneythatbeginstolean or pull away may developcracks or gaps, which allowsmoke and heat to get nearcombustiblematerials,creatingafirehazard.

CRaCkINg/ Cracking, spalling and deterio-DETERIORaTED rated mortar are common

maSONRy OR problems with any exterior mORTaR masonry.

CORBEllINg Chimneys with excessive corbelling (one row of bricks projecting out and overhangingtherowbelow)orundersizedfoundationsarepronetomovement.(SeeSection6.1.1)


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ThREE SIDED Occasionally,chimneysareaddedtotheoutsideofexistinghouses.Manyoftheseareonlythreesided,usingthehousewallasthefourthside.Thisisusuallyconsideredunsafealthoughit may be acceptable where abrickveneerwallismadeofsol-idmasonryunitsand isspacedoutat least1/2 inchfromcom-bustiblesheathing.Onmasonrywalls,12inchesofsolidmasonrymustseparatethefluefromanywood joists or beams. A visualinspection cannot determinewhethertheinstallationissafe.

WOOD Woodbuildingmembersshouldnot contact masonry chimneystoavoidoverheating.

CONTaCTINg Generally speaking, interiorChImNEyS wood should be at least two

inchesfromthechimney.Onex-terior wood,thiscanbereducedto1/2inch.Whereitisnecessarytoframeintothechimney,thereshouldbe12inchesofsolidmasonrybetweenthewoodandtheflue.

FIREBlOCkINg ThespacebetweenmasonrychimneysandwoodframingcanprovideachannelforfiretomISSINg movequicklyupthroughhouse.Fireblockingatceilinglevelshelpspreventthis.Theblock-

ingmaterialcanbecompressedfiberglassinsulationorothernon-combustiblematerial.Itisoftendifficulttoseeduringahomeinspectionwhetherthishasbeeninstalled.

9.0 Things That Cause Structural problems

DESCRIpTION Let’slookatsomeofthecommonthingsthatgowrongwiththestructure.Whiletherearesomeproblemsthatarespecifictoonecomponent(trussupliftproblems,forexample,areuniquetowoodrooftrusses),therearetwobroadsourcesofproblems–poorconstructionandthingsthatattackthebuilding.

9.1 poor Construction

DESCRIpTION Housecomponentsmayfailbecausetheywerebuiltwithimpropermaterials,orthemateri-alswerepoorlyassembled.Examples includeundersizedstructuralmembers likefootings,beams and joists. Poor connection issues include inadequate nailing, missing or poorlyinstalled joist hangers, bad post-to-beam joints, or using the wrong fasteners, like nailsinsteadofboltstosecureadecktoabuilding.

Therearehundredsofexamplesofpoorconstructionpracticescommontohomes.

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9.2 Things that attack houses

DESCRIpTION Let’sassumethehomewasproperlybuilt.Wearenotoutofthewoodsyet!Lotscanstillgowrong,andoftendoes.Someofthethingsthathappenareuniversal,andsomearespecific.Rotandinsectsattackwoodmembersbutnotconcrete,forinstance.We’llstartwithsomethingsthatapplytoallormosthomes,andthenmovetosomethatareregional.

DESCRIpTION 9.2.1 Rot affects Wood: All wood and wood-based building materials are subject to rot.Componentsthataremorelikelytogetwetfrequentlyaremorelikelytorot.

FUNgUS Rotoccursinwoodundercertainconditionsoftemperature,moistureandinthepresenceofoxygen(It’salwayspresent!).Thedecayiscausedbyfungus,whichattacksthewoodcells,causingthecells(andthewoodasawhole)tocollapse.Thefungusthatcausesrotrequiresatemperaturebetwen40°F.and115°F.tobeactive.Abovethattemperature,thefunguscanbekilledand,belowthattemperature,thefungusbecomesdormant,butcanbereactivatedoncethetemperatureincreases.

mOISTURE Sufficient moisture is needed for rot to occur. When the moisture content of the wood NEEDED exceedsapproximately20%,fungussporesthatarenaturallypresentintheatmospherecan

besustainedandgrowwithinthewood.Oncethefungusisestablished,itwillcontinuetogrowanddecaythewoodaslongasthewoodremainswet.Ifthelumberisdriedtobelow20%moisturecontent,therotwillspreadnofurtherandwillbecomedormant.

Astherotprogresses,thewoodcellwallscollapse,leadingtoalossofstrengthandtheforma-tionofcracksperpendiculartoandparalleltothegrain.Thewoodcanoftenbebrokenoffinsmallcubes.

OxygEN Oxygenmustbepresentforrottodevelop.Thisexplainswhywoodsubmergedinwaterwill NEEDED notrot.Undernormalcircumstancesinhouses,thereisalwaysoxygentosupportrotfungi

growth.

RecommendedPracticesandSolutionsforRot

aVOID TRappED Wood structures must be properly designed to resist rot. Wherever possible, the design WaTER shouldpreventcyclicalwettingandentrapmentofmoisture.Alljointsshouldbefreedraining

todryquickly.Ledges,valleysandtroughswherewatercancollectshouldbeavoided.Endgrainsofwoodshouldbewellprotected,astheyarecapableofsoakinguplargeamountsofwaterthroughcapillaryaction.

ROT RESISTaNT Somewoods,includingcedarandcypress,forexample,arenaturallyresistanttodecayfungi. WOOD Variouswoodtreatments(suchaspressuretreating),canenhancetherotresistanceofwood.

Inthecaseofpressuretreating,copperarsenatesalts(typically)areforcedintothewoodcellsunderpressure.Itisthesesaltsthatgivethewoodagreenishtint.Thereareothertreatmentsdesigned to provide resistance to rot, mold and insect attack. They can produce wood ofdifferentcolors,includingblue.

aVOID WOOD/ Avoidingthedirectcontactofwoodwithsoilwillinhibitrotbyhelpingtokeepitdry.Good SOIl CONTaCT ventilationofporchesandcrawlspaces,forexample,isalsoimportantineliminatingrot.


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pREVENT lEakS Appropriate flashing details at joints that promote good drainage, and a well-maintainedprotectivecoatofpaintorstain,willalsohelptofightrot.Leakingroofsandgutters,ifuncor-rected,cancreateanidealenvironmentfortheestablishmentofrotfungi.Similarly,woodintheareaofkitchensandbathroomscanbesusceptibletorotifthereareleakingpipesorfixtures.

DESCRIpTION 9.2.2 Insects attack Wood: Insectscandoseriousdamagetowoodstructures.Termitesdothemostdamagebecausetheyeatthewood,buttherearemanyinsectsthatdamagewoodbynestinginit.Theseincludecarpenterantsandpowderpostbeetles.

Homeinspectorsdonotperformpestinspectionsaspartofahomeinspection.Buttheydolookforevidenceofthestructuraldamagethatresults.Theevidenceisoftenhiddenorverysubtle.

DESCRIpTION 9.2.3 Fire attacks Wood and Steel: Firedamagetoabuildingcanbesevereorcosmetic.Asaverygeneralrule,majorstructuralmemberswithlessthan1/4inchofchardonotrequirere-supporting.This,ofcourse,dependsonthesize,orientationandfunctionofthemember.Wherethereisdoubt,specialistscanbeconsulted.

Anothertypeoffiredamageshouldbeconsidered.Wherewoodstructuralcomponentsaretooclosetofireplaces,furnaces,etc.,thewoodaroundthemmaybegintocharasitoverheats.Thiscanoccurattemperaturesaslowas250°F.Thiswillallowthewoodtoigniteeasilyifex-posedtohighertemperaturesevenbriefly.Charredwoodaroundheatgeneratingappliancesisadangersignthatshouldnotbeignored.

Althoughsteeldoesnotburninthesensethatwooddoes,itlosesitsstrengthquicklywhenexposedtofire.Steelmemberstypicallyfailbeforewoodcomponentsinafire.

DESCRIpTION 9.2.4 Rust attacks metal: Rustorcorrosionaffectsmostmetalstosomeextent.Rustingsteelisacommonhouseproblemwithrespecttopostsandbeamsaswellasfastenerslikenails,screwsandbolts.Unprotectedsteelrustswhenexposedtowater.Steelthatisexpectedtobewetcanbepaintedortreatedwithrustinhibitorssuchasgalvanizing(addingzinctothesteeltoresistrust).Hotdipgalvanizingismoreeffectivethanelectroplategalvanizing,althoughneitherguaranteethattherewillbenorust.Stainlesssteelismorecorrosionresistantthangalvanizedsteelbutisnotcommonasabuildingmaterial.Therearedifferenttypesofstain-lesssteel.

ExpaNDINg RUST Rust can cause metal components to weaken but can also damage other materials. Steelexpands as it rusts, exerting tremendous force. If the steel is embedded in concrete, thedamagecanbesignificant.Steelreinforcingbarscanbreak(spall)concreteandsteelrailingscandamageconcreteporches,decksandbalconies,forexample.

DESCRIpTION 9.2.5 mechanical Damage affects all Building materials: Woodandsteelaremoresuscep-tiblethanconcrete,butdamageispossibleinanyofthese.

Mechanical damage to wood members can take several forms. It may be split, broken orcrushedduringhandlingorwhilethebuildingisunderconstruction.Itiscommonforsomewoodinahomebeingbuilttosufferminormechanicaldamage.Theextentandlocationofthedamagedeterminewhetherreplacementorrepairisneeded.Theentiresystemmustalsobeconsidered.Ifthewall,roof,orfloorsystemissignificantlyover-designed,onedamagedmembermaynotbecritical.

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NOTChES aND Similarconsiderationisgiventomechanicaldamagecausedbycutting,notchingordrilling hOlES holesinwoodmembers.Again,thereareseveralcriteriathathelpdeterminewhethercorrec-

tiveactioniswarranted.

ImpaCT DamagE Impactdamagemaybefromvehicles,animalsorpeople.Thedamagecanbetrivialordevas-tating.

DESCRIpTION 9.2.6 ground movement – Earthquake and Soil Conditions: Nomatterhowwellthehomeisbuilt,whenthegroundbelowmoves,damageislikely.EarthquakesaresignificantproblemsinsomepartsofNorthAmerica.Erosion,landslidesandundergroundstreamsunderminingbuildingsareexamplesoflessdramaticgroundmovement.Homesbuiltonweaksoilsmayfailcatastrophically.Expansivesoilscanalsocausedramaticbuildingdamage.Anotherkindofsoilmovementspecifictocoldclimatesisfrostheave,wherethesoilbeloworbesidethebuildingdamagesconcretefloorsandwalls.

Constructiontechniquescanimprovethechancesofsuccessfullywithstandingdamage,buttherearenoguaranteeswithnature.Duringanearthquake,thehouseshouldactasaunit,with the foundations, floors, walls, and roof moving together. Problems arise when thesemoveindependentlyofeachother.

RISk FaCTOR Unreinforcedmasonrybuildingsandstructuresaremorevulnerabletoearthquakedamagethanwoodframehomes.Woodframehomeswithshearwallsarebetterthanordinarywoodframebuildings.Homeswiththestructuralcomponentstiedtogetherandtiedtothefounda-tionarebetterthanconventionallyframedhouses.Singlestoryhomesarebetterthantwostoryhomes.

COmmON Failuremodesduringearthquakestypicallyincludethingslikepostsmovingoffpiers,beams pROBlEmS movingoffposts,cripplewallsfallingofffoundations,andmasonrychimneyscollapsing.

TWO The two critical strategies in reducing earthquake damage are tying the house structural STRaTEgIES componentstogetherandusingshearwallstominimizerackingofthestructure.

TyINg hOmES Special fasteners are used, both during new construction and in upgrading existing TOgEThER homes. The hardware includes sill anchors (mechanical wedge-type in retrofit situations),

hangers,holddowns(tiedowns),postcaps,strapsandhurricaneclips(hurricaneties).Woodmemberscanalsobeusedtotiecomponentstogether.

SECUREmENT The fasteners may be nailed, bolted or embedded in concrete. Engineers, manufacturersanddesignershavedifferingopinionsaboutthetype,size,locationandnumberoffastenersrequiredinanysituation.Thegoalistotiethebuildingtogethertopreventlateralmovementoroverturning.Thesillsshouldbetiedtofoundationsorfloorslabs,postsshouldbetiedtopiers,beamsshouldbetiedtoposts,floorsshouldbetiedtosills,wallsshouldbetiedtofloorsandsills,androofsshouldbetiedtowalls.

BRaCINg pOSTS Adjacentpostsinsub-gradeareasmaybesupportedwith2x4diagonalbracestohelpresistlateralforces.


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ShEaRWallS Shearwalls help wood frame walls resist racking caused by the strong lateral forces thatoccurduringearthquakes.Shearwallsaretypically3⁄8to1⁄2inchplywoodorwaferboard.Theymustextendthefullheightofthewalltobeeffective.Shearwallsaretypicallytheexteriorwallsofawoodframehome.Someinteriorwallsonlargehomesmayalsobeshearwalls.

DETaIlS Theplywoodorwaferboardpanelsmaybeinstalledontheinnerorouterfacesofstudwalls.Theyarenotneededonboth.Thepanelsareinstalledvertically,exceptoncripplewallslessthanfourfeettall.Gapsofroughly1/8inchareleftaroundalledgesofpanelstoallowforexpansionduetochangesinmoisturecontent.Withoutthesegaps,thepanelsmaybucklewhentheyswell.

SECUREmENT Paneledgesarenailedeveryfourtosixinches,dependingonthedesignerandthesituation,and every 12 inches in the field of the panels. All four edges of panels must be backed bysomethingsolidsuchassills,studs,rimjoists,topplatesorblocking.

hOlD DOWNS Holddownsareprovidedateachcornerofthehomeandateachendofeveryshearwall.HolddownsareheavyL-shapedbracketsthatsecuretheshearwalltothefoundation.Holddownsareusuallysecuredwithbolts.

CRIpplE WallS Cripplewallsareshortwoodframewallsthatspanfromthefoundationtothefirstfloor.Theyare vulnerable to earthquakes because they have little resistance to lateral forces. Cripplewallscanbeconvertedtoshearwallsfromtheinsidebyaddingplywoodorwaferboardpanelstothestuds.Studspacesaretypicallyventedintothesub-gradeareawith1⁄2inchdiameterholesatthetopandbottomofeachstudcavity.

STRap Heavyappliancessuchaswaterheaters,furnaces,refrigerators,washingmachinesandstoves applIaNCES shouldbestrappedtothebuildingtokeeptheminplace. DOWN

SpECIal gaS Gasvalvesthatshutoffautomaticallyifthegaslinerupturescanbeprovidednearthegas ValVES meterinearthquakeproneareas.

ChImNEyS Unreinforced masonry chimneys are common on old homes and there is no easy way to improvetheirresistancetoearthquake.Somepeopleput3/4-inchplywoodonatticfloorsto

preventbricksfallingoffchimneysfromcomingthroughceilingsintothehome.

DESCRIpTION 9.2.7 hurricane and Tornadoes: Earthquakes impose lateral forcesonhomes, for themostpart.Hurricanesexertlateralforcesandupliftforces.Whilesimilartoearthquakesinsomerespects,hurricanes,tornadoesandotherhighwindspresentseparateproblems.

RISk FaCTOR Hurricanesareregionalissues,andthereareotherwind-relatedproblemssuchastwistersandtornadoesthatarealsosomewhatregional.ThesoutheasternUnitedStatesisthemostprominenthurricaneareainNorthAmerica.Severaldevastatinghurricaneshaveoccurredinthisareaandbuildingofficials, insurancecompanies,buildersandhomeownersall lookathomesdifferentlyasaresult.

Considerableinvestigationandresearchhasbeendoneafterhurricanes,andmuchhasbeenlearnedaboutthemechanismsoffailure.Hurricanesusuallycarryheavyrainsandmuchofthedamagefromhurricanesiscausedbywater.Windisnottheonlyissue,butoftencreatestheopeningsthatallowwaterintohomes.Windcarriedprojectilesareanotherproblem.

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kEy ISSUES Manybelievethethreekeyissuesinhurricaneresistanceforhomesare:theroofsheathingmustbewellsecuredtotheroofframing,theroofframingmustbewellsecuredtothewalls,andopeningsincludingdoorsandwindowsmustbeprotectedfromflyingdebris.

DECk NaIlINg Roofsheathingshouldbenailedatsix-inchcentersalongpaneledgesandat12-inchcentersinthefield.Sheathingatoverhangsisoftennailedatfour-inchcentersbecausewindforcescanbegreaterhere.

hURRICaNE ClIpS Hurricaneclipsorstrapsareusedtosecureroofframingtowalls.Strapsarealsousedtofastenwalltopplatestothewallsthemselves.

OpENINgS Openingscanbeprotectedthroughspecialimpactresistantdoorsandwindows,orshutters,plywoodcoversorsomeothershieldingprotectionontheoutside.

ROOF BRaCINg Trussroofscanbestrengthenedwithwoodbracesonthewebsandthechords.Gableendwallshaveprovenvulnerabletohurricanewinds,andareoftenstrengthenedwithbracesintheattic.

WIND RESISTaNT Asphaltshinglesareoftenblownoffroofsduringhurricanesandotherhighwinds.Manu- ShINglES facturershavebeenmakingeffortstoincreasethewindresistanceofroofingmaterials.Some

areascallformopped-inasphaltunderlaymentbeneathshingleswheretheriskofshinglelossissignificant.

CONCRETE TIlES Concretetileshavealsoblownoffroofsinhurricanes.Theseareworsethanasphaltshinglesbecause the heavy tiles become dangerous projectiles. Improved installation techniquesincludefullmortarbedsforconcretetiles.

hIp ROOFS Designersarebeingencouragedtomovefromgableroofstohiproofs,sincehipsare lesslikelytofail.Hiproofshavenoverticalgablewallto‘catchthewind’.

gaRagE DOORS Garagedoorshavebeenaproblembecausetheyblowineasily.Strongerdoors,hardwareandtracksareapartialsolution.

NO gUaRaNTEES Aswithearthquakes,homescanbebuilttoimprovetheirchanceofsurvivingseriouswinds,butnatureissostrongthattherearenoguarantees.

DESCRIpTION 9.2.8 Flood:Flooddamagecanbesevereandmaybethemostseriousimpactofhurricanesandearthquakes.

Homesinfloodproneareasmaybebuiltonstiltstoreducetheriskofdamageorlossofbuild-ing,buttherearefewabsoluteswithflooding,aswithothernaturalforces.


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hrb 3 structure 2012 8.5x10.875 - carson dunlop 76 introduction ... windows in basements are usually...

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