understanding and improving performance of new manufactured homes ...€¦ · understanding and...

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Understanding and Improving Performance of New Manufactured Homes During High-Wind Events FEBRUARY 2007 TORNADO RECOVERY ADVISORY FEMA DR 1679 RA5 Purpose and Intended Audience The purpose of this Tornado Recovery Advisory is to provide guidance on reducing damage to new manufactured homes from high-wind events including tornadoes and hurricanes. For this recovery advisory, any manufactured home constructed after July 13, 1994 is considered a new manufactured home. Guidance for improving manufactured homes constructed before July 13, 1994, is contained in the Tornado Recovery Advisory titled Understanding and Improving Performance of Older Manufactured Homes During High-Wind Events. This recovery advisory has been prepared for owners of new manufactured homes. Prospective purchasers of manufactured homes, building offcials, manufactured home installers, contractors, and operators of manufactured home communities may also fnd it informative. This Recovery Advisory Addresses: Manufactured home ages Vulnerabilities of new manufactured homes to tornadoes and hurricanes Recommendations 1 Manufactured Home Ages Although there are no strict defnitions of “older” and “new” manufactured homes, the following descriptions, which are based on See these 2007 Tornado Recovery Advisories for information about tornado risk, sheltering from tornadoes, and improving manufactured homes against damage from high winds: Tornado Risks and Hazards in the Southeastern United States (Tornado Recovery Advisory No. 1) Storm Shelters: Selecting Design Criteria (Tornado Recovery Advisory No. 2) Residential Sheltering: In- Residence and Stand-Alone Shelters (Tornado Recovery Advisory No. 3) Understanding and Improving Performance of Older Manufactured Homes in High-Wind Events (Tornado Recovery Advisory No. 4) the evolution of manufactured home construction standards, are useful. “Older” Manufactured Homes: This category includes “pre-code” homes and “early code” homes. Some manufactured homes considered “older” may be relatively new from an expected service life standpoint, but are still old from a wind resistance standpoint. For this recovery advisory, any manufactured home constructed before July 13, 1994 is considered an older manufactured home. Pre-Code Manufactured Homes: This refers to homes built before June 15, 1976, when the Department of Housing and Urban Development (HUD) began regulating construction. Prior to 1976, manufactured housing was essentially unregulated and wide variations in construction quality and strength existed. Pre- code manufactured homes were often called trailers or mobile homes because they were intended to be moved from place to place. Early Code Manufactured Homes: These are homes built after June 15, 1976 (and before July 13, 1994) when the Manufactured Home Construction and Safety Standards (MHCSS), developed by HUD, frst 1. Actions recommended by this recovery advisory will reduce damage to manufactured homes during tornadoes or hurricanes. The actions will not, however, strengthen newer manufactured homes enough to allow occupants to safely remain in their homes during a high-wind event. When advised by local or State authorities, occupants of manufactured homes should fnd suitable shelter when tornadoes or hurricanes threaten. Understanding and Improving Performance of New Manufactured Homes During High-Wind Events HSFEHQ-07-J-0007 / April 2007 Page of 8

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Page 1: Understanding and Improving Performance of New Manufactured Homes ...€¦ · Understanding and Improving Performance of New Manufactured Homes During High-Wind Events FEBRUARY 2007

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Understanding and Improving Performance of New Manufactured Homes During High-Wind Events FEBRUARY 2007 TORNADO RECOVERY ADVISORY FEMA DR 1679 RA5

Purpose and Intended Audience ThepurposeofthisTornadoRecoveryAdvisoryistoprovideguidance onreducingdamagetonewmanufacturedhomesfromhigh-windevents includingtornadoesandhurricanes.Forthisrecoveryadvisory,any manufacturedhomeconstructedafterJuly13,1994isconsidereda newmanufacturedhome.Guidanceforimprovingmanufacturedhomes constructedbeforeJuly13,1994,iscontainedintheTornadoRecovery AdvisorytitledUnderstanding and Improving Performance of Older Manufactured Homes During High-Wind Events.

Thisrecoveryadvisoryhasbeenpreparedforownersofnew manufacturedhomes.Prospectivepurchasersofmanufactured homes,buildingofficials,manufacturedhomeinstallers,contractors, andoperatorsofmanufacturedhomecommunitiesmayalsofindit informative.

This Recovery Advisory Addresses:

Manufacturedhomeages

Vulnerabilitiesofnewmanufacturedhomestotornadoesand hurricanes

Recommendations1

Manufactured Home Ages Althoughtherearenostrictdefinitionsof“older”and“new” manufacturedhomes,thefollowingdescriptions,whicharebasedon

Seethese2007Tornado RecoveryAdvisoriesfor informationabouttornado risk,shelteringfrom tornadoes,andimproving manufacturedhomesagainst damagefromhighwinds:

TornadoRisksandHazards intheSoutheasternUnited States(TornadoRecovery AdvisoryNo.1)

StormShelters:Selecting DesignCriteria(Tornado RecoveryAdvisoryNo.2)

ResidentialSheltering:In-ResidenceandStand-Alone Shelters(TornadoRecovery AdvisoryNo.3)

Understandingand ImprovingPerformance ofOlderManufactured HomesinHigh-WindEvents (TornadoRecoveryAdvisory No.4)

theevolutionofmanufacturedhomeconstructionstandards,areuseful.

“Older” Manufactured Homes: Thiscategoryincludes“pre-code”homesand“earlycode”homes.Some manufacturedhomesconsidered“older”mayberelativelynewfromanexpectedservicelifestandpoint,but arestilloldfromawindresistancestandpoint.Forthisrecoveryadvisory,anymanufacturedhomeconstructed beforeJuly13,1994isconsideredanoldermanufacturedhome.

Pre-Code Manufactured Homes:ThisreferstohomesbuiltbeforeJune15,1976,whentheDepartment ofHousingandUrbanDevelopment(HUD)beganregulatingconstruction.Priorto1976,manufactured housingwasessentiallyunregulatedandwidevariationsinconstructionqualityandstrengthexisted.Pre­codemanufacturedhomeswereoftencalledtrailersormobilehomesbecausetheywereintendedtobe movedfromplacetoplace.

Early Code Manufactured Homes:ThesearehomesbuiltafterJune15,1976(andbeforeJuly13,1994) whentheManufacturedHomeConstructionandSafetyStandards(MHCSS),developedbyHUD,first

1. Actionsrecommendedbythisrecoveryadvisorywillreducedamagetomanufacturedhomesduringtornadoesorhurricanes.Theactionswillnot, however,strengthennewermanufacturedhomesenoughtoallowoccupantstosafelyremainintheirhomesduringahigh-windevent.Whenadvised bylocalorStateauthorities,occupantsofmanufacturedhomesshouldfindsuitableshelterwhentornadoesorhurricanesthreaten.

Understanding and Improving Performance of New Manufactured Homes During High-Wind Events HSFEHQ-07-J-0007/April 2007 Page � of 8

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wentintoeffect.After1976,homesbecameknownas“manufacturedhousing.”TheMHCSSspecified minimumwindpressuresthatmanufacturedhomesmustbedesignedtoresist.Italsocontainedgeneral criteriaforanchoringhomestoresistwindforces.ThewindpressuresrequiredbytheMHCSScorrespond toasustainedwindspeedofaround70milesperhour(mph)inanExposureCarea.Thisisapproximately equivalentto85mphpeakgustwinds.

“New” Manufactured Homes:HurricaneAndrewdestroyednumerousmanufacturedhomesin1992.In responsetothisdamage,theMHCSSstandardswerestrengthenedonJuly13,1994.Thestrengthened standardsapplytohomesplacedinhigherwindspeedareas.These1994revisions,whichremainineffect today,establishedthreetypesofhomes:HUDZoneI,HUDZoneII,andHUDZoneIIIhomes.

HUDZoneIhomesarethosehomesdesignedtotheoriginal1976standards.

HUDZoneIIhomesaredesignedtoresistsustainedwindspeedsof100mph (equivalenttoapproximately120mphpeakgustwinds).

HUDZoneIIIhomesaredesignedtoresistsustainedwindspeedsof110mph (equivalenttoapproximately130mphpeakgustwinds).

InFloridanew homesmustbe HUDZoneIIor HUDZoneIII.

Wind damage to a new manufactured home.

NOTE:“Sustained”windspeedsareapproximatelyfastestmilewindspeeds;“gust” windspeedsareapproximately3-secondgustswindspeeds.

How New Manufactured Homes are Vulnerable to Tornadoes and Hurricanes Properlyinstalledandmaintainedmanufactured homesdesignedandinstalledtothe1994 HUDstandardperformmuchbetterthanolder manufacturedhousing,particularlyinareaswith higherdesignwindspeeds.However,evennew manufacturedhomesareoftendamagedbyhigh-wind events.Damagecanbegroupedintotwocategories: directdamagetothehomeitselfanddamagethat resultsfromfailuresinthehome’sanchoragesystem. Althoughmanufacturedhomesandsite-builthomes mayhavesimilarvulnerabilitiestodirectdamage, someofthevulnerabilitiestoanchoragefailuresare uniquetomanufacturedhomes.

Direct Damage

Directdamageoftenincludesblown-offroofpanels, lossofroofframing,lossofwallpanelsandframing, andbreakageofunprotectedwindows.Windowdamage occursasaresultofhighwindpressuresorfromthe impactofflyingdebrisgeneratedbyhighwinds.

Directdamagetonewmanufacturedhomesusually resultsfromconnectionfailures.Nailsorstaples usedtosecureroofing,siding,roofsheathing,or wallsheathingcanbeoverloadedduringhigh-wind events.Nailsorstaplescaneitherbepulledoutor thematerialtheysecurecanbetornawayfromthe headsofthenailsortopsofthestaples.

Attachments:Thepotentialfordamageto manufacturedhomesincreasessignificantlywhen additionslikecarports,awnings,orporchesare fastenedtothehome.Theseadditionsconcentrate windforceswheretheyarefastenedtothehome. Theincreasedforcescanoverloadconnectionsused

Damage to new manufactured home resulting from improper carport attachment.

Damage to new manufactured home resulting from improper attachment of a screened enclosure.

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Glazing damage caused by windborne debris from nearby damaged homes and attachments.

toholdthehometogetherandcausefailureofthe membersorconnectionsinthehome.

Mosthomemanufacturersprohibitattachmentsto theirhomesunlessspecialprovisionstosupport attachmentswereincorporatedintothehomewhen itwasmanufactured.Theattachmentsthemselves, unlessengineered,alsoviolatelocalcode requirementsinmanyjurisdictions.

Windborne Debris:Damagefromwindborne debrisisalsocommoninmanufacturedhomes. Newmanufacturedhomessitedincommunities thatcontainoldermanufacturedhomesorin

communitieswhereattachedstructuresareprevalentareparticularlyvulnerable.Thosehomesandattached structuresareoftendamagedfromhigh-windevents.Theresultingdebrisformsmissiles,whichcanstrike surroundinghomes.

Manufactured Home Anchorage

Anchoragefailuresinvolvethehomebeinglifted,slid,orrolledoffitsfoundation.Ananchoragefailurecandestroy ahomeevenwhenthereisnodirectwinddamagetothehomeitself.

HUDstandardsrequirethatthemanufacturersofallhomesincludeprovisions(atleastonemethod)for securingandanchoringhomestoresistwindforces.ForhomesdesignedtobeinstalledinWindZoneIareas, thedesigncriteriainthestandardsrequireonlydiagonal(orframe)tiestobesecuredtothemainframe members(usuallytwosteelI-beamsundereachsection).ForhomesdesignedtobeinstalledinWindZone

IIareas,thestandardsrequirethat homesbeprovidedwithvertical walltiesateachframetielocation oranchor.IntheStateofFlorida, statutescontainedintheDepartment ofHighwaySafetyandMotorVehicles DivisionofMotorVehiclesChapter 15C-1alsorequirelongitudinal tiestoresistmanufacturedhome movementalongthelengthofthe home.

Inmostmanufacturedhomes, anchorageisprovidedbyground anchorsandsteelstraps.Ground anchorsconsistofasteelshaft (preferablygalvanizedtoresist corrosion)andoneortwohelical steelplatesthatareauguredintothe earth.Mostgroundanchorscontain headsspecificallydesignedtoaccept thesteelstrapsthatconnectthe anchortothehome’sframesandwall ties.Groundanchorsinstalledat, ornear,averticalanglearetypically providedwithstabilizerplatesto increasetheirresistancetolateral movementordisplacement.

Bytheirverynature,groundanchors movewhenloadsareapplied.During ahigh-windevent,windsapplyloads

Typical ground anchor supports for HUD Zone II and Zone III homes. tothehome,whichinturnapplies loadstothegroundanchors.Ground

Typical ground anchor supports for a HUD Zone I home.

Understanding and Improving Performance of New Manufactured Homes During High-Wind Events HSFEHQ-07-J-0007/April 2007 Page � of 8

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This home, which was secured with ground anchors, moved After falling from its supports, the home moved approximately enough to allow it to fall from its supporting piers. 3 feet.

Fractured ABS stabilizer plates may have contributed to the failure of the support system.

Fractured ABS stabilizer plate

Wall ties that secured the home to ground anchors were torn from the home.

When the home shifted, anchor straps became loose.

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anchorsaretypicallyallowedtomoveupto3incheslaterallyor2inchesverticallytoresistwindloads. Whenahomeissecuredwithgroundanchors,ittoocanmoveupto3incheslaterallyor2inchesvertically. Theamountofmovementthatamanufacturedhomesecuredwithgroundanchorsmayexperiencegreatly exceedstheamountofmovementexperiencedbysite-builthomes(ormanufacturedhomes)properlyplaced onconventionalfoundations.

Duringhigh-windevents,homessecuredwithgroundanchorsmaymoveenoughtoforcethemofftheir supportingpiers.Thisriskexistsevenfornewlyinstalledhomes.Thehomeshowninthephotosonthe previouspagewasinstalledinNovember2006andwasdamagedbytheFloridatornadoesofFebruary2007. Whilethehomefelloffitspiers,thelimiteddamagetosidingandroofsheathingsuggeststhatthehomewas notexposedtodesign-levelwindforces.

Recommendations Home Strengthening

Addingfastenerstoimprovewindperformanceusuallyinvolvesremovingsiding,roofing,orsheathing. Typically,thistypeofimprovementcanbestbedonewhenrepairsormaintenancearebeingcompleted onahome.Whilebuildingcodesdonotspecificallyapplytomanufacturedhousing,designscontained inprescriptivecodesandstandards,suchastheInternational Residential Code(IRC2006),contain fasteningschedulesforwallandroofsheathingthatmaybeappropriateforimprovingwindperformancein manufacturedhomes.Otherconnections,suchasrafter-to-wallconnections,canbedesignedbyregistered engineersorarchitects.

Roofingcanbedamagedbyhighwindsandwindbornedebris.Duringreroofingprojects,improvementscan beinstalledtomaketheroofcoveringanddecklessvulnerabletowindanddebris.Forhomeswithasphalt shingledroofing,TechnicalFactSheetsNo.19and20inFEMA499,Home Builder’s Guide to Coastal Construction2(2005),providesguidanceoninstallingasphaltshinglestoimproveupliftresistanceandreduce vulnerabilitytodamageduringhigh-windevents.Asphaltshinglesaresuitableforroofswithslopes3:12or greater.

Attachments and Attached Structures

Homeownersareadvisedthatmanyhomeswerenotdesignedorapprovedbythemanufacturertohave attachmentsconnectedtotheunits.Attachedstructuresshouldnotbeaddedtohomesnotdesignedto supportthem.Regardlessofwhethertheaddedstructureisattachedtothehomeorisfree-standingnext toit,alladdedstructuresshouldbeconstructedtomeetlocalcoderequirementsusingthesamestandards asthoseforresidentialsite-builtconstruction.Thedesignofadditionsshouldnotusereducedwindcriteria thatisoccasionallyconsideredforancillarystructureslikeagriculturalbuildingsandminorstoragefacilities. Wherenocodeisadopted,the2006International Residential Code,the2006International Building Code,or the2006editionofNationalFireProtectionAssociation(NFPA)5000Building Construction and Safety Code shouldbefollowed.

Generally,allexistingattachmentsshouldeitherberemovedorreconfiguredsotheyaresupported independentlyofthehome.Forbestperformance,noconnectionsshouldremainbetweenthemanufactured homeandtheattachedstructure,otherthanflashingrequiredforweather-tightness.Anattachmentmaynot needtoberemovedorreconfiguredifthehomehasreinforcedstructuralelementsthatcansupportit.The homeownershouldrefertothemanufacturer’sinstructionstodeterminewhetherthehomewasdesigned toaccommodatetheattachedstructure.Itmaybenecessarytocontactalocalengineerforassistancein makingthisdetermination.

Newattachmentsorstructuresshouldbedesignedandconstructedperthe2006International Residential Code,the2006International Building Code,orthe2006editionofNFPA5000.

Protection from Windborne Debris

Properlyinstalledshuttersareeffectiveatpreventingbrokenglazingfromwindbornemissilesandthe resultingdamagefromwind-drivenraininfiltration.HUDregulationsrequirethatwallframingbeprovidedto

2. FEMA499isavailableonlineathttp://www.fema.gov/rebuild/mat/mat_fema499.shtm.Hardcopiesmaybeobtainedatnocostbycalling800-480­2520.

Understanding and Improving Performance of New Manufactured Homes During High-Wind Events HSFEHQ-07-J-0007/April 2007 Page � of 8

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allowtheinstallationofhurricaneshuttersatallwindowsanddoorsin HUDZoneIIandZoneIIIhomes,butdoesnotrequiretheinstallationand useofshutters.

Anchorages and Strapping

Anchorsandstrapsshouldbeinspectedregularlyandallcorrodedstraps oranchorsshouldberemovedandreplaced.Ininteriorareas(morethan 3,000feetfromthecoast)anchorsandstrapsshouldbeinspectedevery 5years.Forhomessituatedwithin3,000feetofthecoast,anchorsand strapsshouldbeinspectedevery2years.Whennewanchorsandstraps areinstalled,onlygalvanizedmaterials(withaminimumcoatingof0.6 ouncepersquarefoot)shouldbeused.Anchorheadsshouldremain1 to2inchesaboveadjacentgradetohelppreventcorrosionresultingfrom

Seriousconsideration shouldbegivento installingshuttersonZone IIandZoneIIIhomes whentheyareinstalled inhighwindareaswhere thebasicwindspeed identifiedinthelocal buildingcoderequiresthe useofglazingprotection forsite-builtconstruction.

wateraccumulatingneartheanchorheadandstrap.

Ground Anchors

Groundanchorsmustbeproperlyselectedbasedonthesoilspresent atthesite.Looseorpoorlyconsolidatedsoilsrequiredeeperanchors withlargerhelicalplatestoprovidethestrengthnecessarytoresistwind loads.Moresubstantialfoundations,likeconcretestripfootings,maybe requiredinareaswithpoorsoils,withsaturatedsoils,orinareaswherea permanentfoundationisdesired.

Homesshouldbeanchoredinboththelateralandlongitudinaldirection. Manufacturersmayalsorequireadditionalanchorageundershearwalls andalongthemating(marriage)wallbetweendouble-widehomes.Lateral anchoragerequirementsdependonthedesignwindspeedfortheareaand onthelengthandwidthofthehome.Thegreaterthedesignwindspeed, theclosertherequiredanchorspacing.Also,narrowsingle-widehomes, whicharemorepronetooverturning,requirecloseranchorspacingthanwiderdouble-widehomesandlonger homesrequiremorelateralanchorsthanshorterhomes.Thetypeofpadsusedunderthemasonrypiersthat supportthehomeshouldalsobeconsidered.CloseranchorspacingissuggestedwhenABS(Acrylonitrile ButadieneStyrene)padsareused.ABSpadsarearelativelynewstyleofpadthatisusedinlieuofheavier concretepads.Theyarelightweightandtypicallymanufacturedfromrecycledplastics.Closeranchorspacing shouldlimithomemovementandshouldhelppreventfracturingoftheABSpads.Lateralgroundanchors shouldalsobeplacedwithin2feetoftheendsofthehome.Usethetablethatfollowstoidentifymaximum

HomesinSpecialFlood HazardAreas(SFHAs)and homeslocatedwheresoils maybesaturatedshould followanchorspacing andpierconstruction recommendedinFEMA85, Multi-Hazard Foundation and Installation Guidance, duetobecompletedin 2007.

Lateral Ground Anchor Spacing Single Wide Double Wide

Design Wind Speed ABS Pads Concrete Pads ABS Pads Concrete Pads

90 mph 5’4” 6’8” 5’4” 6’8”

��0 mph 5’4” 6’8” 5’4” 6’8”

��0 mph 4’0” 5’4” 4’0” 5’4”

NOTES: (1)Thedesignwindspeedisthe3-secondgustwindspeedperASCE7-05andthe2006editionoftheInternationalBuilding

Code.TheanchorspacinglistedaboveisappropriateforExposureBandCconditions.Alicensedprofessionalengineer shoulddesignanchorageforhomesplacedinExposureDareasandforhomesplacedwithin1,500feetofthecoast(as requiredbytheMHCSS).

(2)Groundanchorspacingisbasedonhomesweighinganaverageof20poundspersquarefoot,withsteelI-beamframes spacedatintervalsof96inchesormore,withroofslopesbetween15degreesand20degrees,andwithwallheightsup to8feet.Thespacingisappropriateforhomesplacedonmasonrypiersupto36inchestall.Whenthemanufacturer’s installationinstructionsarenotavailable,alicensedprofessionalengineershoulddesignanchorspacingforhomesthat weighless,havenarrowerI-beamframespacingortallerwalls,areplacedontallerpiers,orhavesteeperorshallowerroofs.

(3)Whenthemanufacturer’sinstallationinstructionsorlocalcodesspecifygroundanchorspacingdifferentthanthatlisted above,anchorsshouldbeinstalledattheclosestanchorspacingspecifiedforimprovedresistancetohurricanesandtornadoes.

ThegroundanchorspacingsshownaregreaterthanFlorida15C-1requirements.ForhomesinFlorida,locateanchorsat 5feet,4inches(maximum).

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intervalspacingandcalculatethenumberofanchorsneededforlateral anchorage.Forexample,ifadouble-widehomeissitedina110mph windzoneandplacedonconcretepads,itshouldhavegroundanchors spacedatmaximumintervalsof6feet,8inches.Therefore,a64-foot-long double-widehomewouldrequire20lateralanchors(10perside)anda 72-foot-longdouble-widehomewouldrequire24anchors.Forlongitudinal anchorage,4groundanchorspersectionendarerecommended.Atotal of8longitudinalgroundanchorsshouldbeinstalledforsingle-widehomes and16shouldbeinstalledfordouble-widehomes.

Maintain Anchors and Straps

Whenahomeisallowedtomove,evenslightly,anchorsandstrapscan becomeloose.Loosestrapsrenderanchorsineffectiveatresistingwind. Anchorstrapscanloosenevenwithoutahomebeingexposedtohigh winds,particularlyifsoilsarerelativelysoftorifanchorswereinadequately pre-tensionedaftertheirinstallation.Becauseofthis,manufactured homessecuredwithgroundanchorsshouldhavetheiranchorschecked periodicallyandre-tensionedwhenstrapsarefoundloose.

Routineinspectionand maintenanceshould include:

Inspectanchorsand straptensionandtighten whenstrapsarefound loose.Ininteriorareas (morethan3,000feet fromthecoast),anchors andstrapsshouldbe inspectedevery5years. Incoastalareas,anchors andstrapsshouldbe inspectedevery2years.

Replaceallcorroded strapsandanchors.

High-windevents cancausehomes securedwithground anchorstoshift acrosstheirpiers. Thisshiftincreases loadsonportions ofthefootings belowthepiers whichincreasesthe potentialforfooting damage.Shifting alsomakesthehome morevulnerableto anchoragefailures duringsubsequent events.Whenthe centerlinesofthe home’sframeare notlocatedwithin 2½inchesofthe centersofthepiers, thehomeshouldbe liftedandre-setto properlycenterthe home’ssteelframes overthecentersof thepiers.

Improve Anchorage by Using In-Line Anchors

Homeownersshould considerreplacing

SCHEMATIC IN-LINE ANCHORAGE fOR HUD ZONE I HOMES

SCHEMATIC IN-LINE ANCHORAGE fOR HUD ZONE II AND ZONE III HOMES

Improved installation using in-line ground anchor installed at a 45 degree angle. The installation reduces the amount a home will move during tornadoes and hurricanes.

verticallyinstalledanchorsusedwithstabilizerplateswithanchorsinstalledata45-degreeangle.When exposedtowindloadsanchorsinstalledata45-degreeangle(alsocalledin-lineanchors)movelessthan verticallyinstalledanchorsusedwithstabilizerplates.FEMA-fundedgroundanchortestsconductedinFlorida in2001revealedthesuperiorperformanceofanchorscommonlyusedinFloridawhentheywereinstalled

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ata45-degreeangle.Indrysoils,5-foot-longanchorsinstalledata45-degreeanglemoved30percentless thanverticallyinstalledanchorsusedwithstabilizerplates.Insaturatedsoils,thedifferencesweremore pronounced.Five-foot-longanchorsinstalledata45-degreeanglemoved60percentlessthanvertically installedanchorsusedwithstabilizerplates.Installinganchorsata45-degreeanglerequiresmoreclearance underahomethantheclearancerequiredforverticallyinstalledanchorsusedwithstabilizerplates.Pre­drillingholesfortheanchorhelixesallowsanchorstobeinstalledata45-degreeanglewhenlowerclearances exist.Pre-drillinguptoonethirdthelengthofananchorisallowedbymostanchormanufacturers,provided theexcavatedsoilsarecompactedaftertheanchorisinstalled.

Conventional Foundations

Whenselectingafoundation,ownersofmanufacturedhomesshouldconsiderfoundationssuchasthose usedforsite-builthomes.Thesetypesoffoundationscanbeusedtosupportmanufacturedhomesand requirelessmaintenancethangroundanchorfoundations.Conventionalfoundationsalsoperformbetterthan groundanchorfoundationsduringhigh-windevents.

Perimeterfoundations,likethoseusedtosupportsite-builthomes,areoneoption.Thosefoundationsare typicallyconsideredpermanentand,inadditiontoimprovedstabilityandperformance,theymayalsoallow homeownerstobenefitfromlowermortgageinterestrates.Perimeterfoundationstypicallyrequiretheuseof acranetoliftthemanufacturedhomeandplaceitontheperimeterfoundation,therebyincreasingthecostof installation.

Example of concrete strip footing foundation.

Asecondfoundationoptionistoplacethemanufacturedhomeonconcretestripfootingsandmasonrypiers likethoseshownbelow.Concretestripfootingsandpiersoffertheadvantageofnotrequiringacranetoplace amanufacturedhome;ifproperlydesigned,thesefoundationscanprovideimprovedstabilityandperformance thatapproachesthatofaperimeterfoundation.

ForhomeslocatedinZonesI,II,andIII,continuousconcretestripfootingsareplacedunderthesteelframes ofthehome.Thefootingsneedtobeplacedonfirmsoilsatanadequatedepthtomeetlocalbuilding coderequirements.Reinforcedpiersarethenconstructedandstrappedtotheframesandanchoredtothe footings.Cross-strapsconnectingfootingstooppositeframesproviderigidity.ForhomeslocatedinZonesII andIII,perimeterstripfootingsareneededforconnectionstowallties.

HomeslocatedinSpecialFloodHazardAreas(SFHAs)shouldfollowinstallationrecommendationscontained intherevisedFEMA85,Manufactured Homes in Flood Hazard Areas – A Multi-Hazard Foundation and Installation Guide.TherevisedFEMA85isduetobecompletedin2007.Thegroundanchorspacingtable includedinthisRecoveryAdvisorywasdevelopedfromFEMA85.

Page 8 of 8 Understanding and Improving Performance of New Manufactured Homes During High-Wind Events HSFEHQ-07-J-0007/April 2007