tornado risks and hazards in the southeastern united states

Page � of 6Tornado Risks and Hazards in the Southeastern United States HSFEHQ-07-J-0006/April 2007

Purpose and Intended AudienceThepurposeofthisTornadoRecoveryAdvisoryistoprovidebackgroundonthetornadohazardintheSoutheast.Thegeneralpopulation,homeownersandrenters,policymakers,localofficials,builders,andbuildingdepartmentsshouldunderstandthattornadooccurrenceintheSoutheastisnotarareevent.Infact,ofthetop20statesintornadofrequency,5areintheSoutheast.

ThisadvisoryalsoidentifiesFEMAresourcesthatcanbeusedtohelpdesignandconstructportionsofalmostanybuildingtype(includingresidences)toprovidesafeshelterfromtornadoes,ortohelpminimizedamagecausedbythesewindevents.

This Recovery Advisory Addresses:

Recentevents

Tornadooccurrenceoutside“TornadoAlley”…howgreatistherisk?

Canabuildingsurviveatornado?Yes!

Assessingrisk

Weatherradios

Recent EventsIntheearlymorninghoursofFebruary2,2007,asmallbutdevastatingoutbreakofthreetornadoesstruckcentralFloridafromLadyLaketoNewSmyrnaBeach.TwoofthetornadoeswereratedbytheNationalWeatherServiceasEF3andtheotherwasratedEF1ontheEnhancedFujitaScale(seetextbox).Thethreetornadoesstruckinthemiddleofthenight.Twenty-onepeoplewerekilledanddozenswereinjured.Totaldamageestimatesarestillbeingcompiledfromthisevent,butearlyestimatesarethatmorethan$150million1indamagewascausedbythesetornados.Lessthanonemonthlater,onMarch1,2007,Enterprise,Alabamaexperiencedone

Seethese2007TornadoRecoveryAdvisoriesforinformationaboutshelteringfromtornadoes,andimprovingmanufacturedhomesagainstdamagefromhighwinds:

StormShelters:SelectingDesignCriteria(TornadoRecoveryAdvisoryNo.2)

ResidentialSheltering:In-ResidenceandStand-AloneShelters(TornadoRecoveryAdvisoryNo.3)

UnderstandingandImprovingPerformanceofOlderManufacturedHomesinHigh-WindEvents(TornadoRecoveryAdvisoryNo.4)

UnderstandingandImprovingPerformanceofNewManufacturedHomesinHigh-WindEvents(TornadoRecoveryAdvisoryNo.5)

FEBRUARY 2007 TORNADO RECOVERY ADVISORY FEMA DR-1679-RA1

Tornado Risks and Hazards in the Southeastern United States

TheFujitaScalecategorizestornadoseveritybasedonobserveddamage.Thesix-stepscalerangesfromF0(lightdamage)toF5 (incredible damage). As of February 2007, the NationalWeatherServiceusestheEnhancedFujitaScale(EFScale).ThisnewscalerangesfromEF0toEF5.Seehttp://www.spc.noaa.gov/efscale/forfurtherinformationontheEFScale.

Fujita Scale EF Scale

FujitaScale

3-Second Gust Speed (mph) EF Scale

3-Second Gust Speed (mph)

F0 45–78 EF0 65–85

F� 79–117 EF1 86–109

F2 118–161 EF2 110–137

F3 162–209 EF3 138–167

F4 210–261 EF4 168–199

F5 262–317 EF5 200–234

1. St.PetersburgTimes,“FacingLifeWithoutFamily”byCatherineShoichet,March2,2007.

Tornado Risks and Hazards in the Southeastern United States HSFEHQ-07-J-0006/April 2007 of 6

ofthetop10deadliesttornadoestoimpactaschoolwhen,intheearlyafternoonhours,atornadorippedthroughahighschool,killingeightstudents.Laterthatday,atornadoseverelydamagedahospitalinAmericus,Georgia.TheMarch1stormscauseddamageandlossoflifeinseveralareasofbothstates.

Tornado Occurrence Outside “Tornado Alley”… How Great Is the Risk?“TornadoAlley”isanareaoftheheart-landoftheUnitedStatesknownforitstornadoactivity.AlthoughtheexactextentofTornadoAlleycanbedebated,mostscientistsagreethatTexas,Oklahoma,andKansasarewellknownfortornadoriskandmakeupalargeportionofTornadoAlley.

WhatmostpeoplemaynotbeawareofistheamountoftornadicactivityoutsideofTornadoAlley.FEMARegionIVhaseightstatessubjecttotornadoesandsixsubjecttohurricanes(refertomaponthispage).

AlthoughhurricaneshavereceivedmostoftheattentioninrecentyearsintheSoutheast,thethreatandriskoftornadoesisreal.ThetablebelowshowsthenumberoftornadooccurrencesforeachofthestatesinFEMARegionIV.Forthe55-yearstudyperiod,over9,700tornadoeshavebeenrecorded.TheStateofFloridaalonehasseenextremenumbersoftornadooccurrences.Forthreeoftheyearsbetween1997and2004,itexperiencedover100tornadoes(115in1997,115in1998,and105in2004).

MosttornadoesoccurringintheSoutheast(withtheexceptionofMississippiandAlabama)aretypicallyweakormoderatelystrong(classifiedasF2andsmallerontheFujitaScale).However,theseweakertornadoescanbeasdeadlyasthestrongerF3,F4,andF5tornadoes.Forexample,over50ofthe78killertornadoesthatoccurredinFloridabetween1882and2007wereF2orweaker.Further,tornadoesarenotalwayssingletornadoevents;sometimesoutbreaksofseveraltornadoesareassociatedwithalargestormsystem.NotableoutbreaksintheSoutheastinclude:

The Carolinas Outbreak of March 28, 1984

22tornadoesresponsiblefor57fatalities

Approximately1,250injuries

Approximately$200millionindamages

37%offatalitiesoccurredinmanufacturedhomes

The Kissimmee Tornado Outbreak of February 22–23, 1998

7tornadoesresponsiblefor42fatalities

Approximately200injuries

Over$100millionindamages

ThreestrongesttornadoeswereratedF3,whichdestroyedover300buildingsanddamagedmorethan7,000

States inFEMA

Region IV

Total Tornado Occurrences (�950–2005)

Total Fatalities(�950–�995)a

Number Rank

Florida 2,799 85b

Mississippi 1,429 387 2

Alabama 1,301 282 4

Georgia 1,143 111 14

North Carolina 935 82

Tennessee 788 184 7

South Carolina 718 47

Kentucky 590 105 15a. Texasisrankedhighestwith475fatalitiesforthisperiodof

time.b. InFlorida,anadditional21fatalitiesoccurredbetween1995–

2007,foratotalof166(1950–2007).

of 6Tornado Risks and Hazards in the Southeastern United States HSFEHQ-07-J-0006/April 2007

Frequency of Recorded F3, F4, and F5 Tornadoes(�950–�998)

SOURCE:FEMA361,Design and Construction Guidance for Community Shelters, July2000

Assessing Your RiskTodetermineifyouhavealow,moderate,orhightornadorisk,usetheFrequencyMap(below)todeterminehowmanytornadoeswererecordedper3,700squaremilesfortheareawhereyourbuildingislocated.Findtherowinthe“RiskTable”(below)thatmatchesthatnumber.Next,lookattheWindZoneMap(nextpage)andnotethewindzone(I,II,III,orIV)inwhichyourbuildingislocated.FindthematchingcolumnintheRiskTableandfindtheboxthatlinesupwithboththenumberoftornadoesper3,700squaremilesinyourareaandyourwindzone.Thecolorinthatboxtellsyouthelevelofyourriskfromextremewindsandhelpsyoudecidewhethertobuildashelter.Ashelteristhepreferredmethodofwindprotectioninhigh-riskareas.

Number of Tornadoes per 3,700 Square Miles (see Wind Zone Map)

Wind Zone (see Frquency Map)

I II III IV

<� LOW Risk LOW Risk « LOW Risk « MODERATE Risk

�–5 LOW Risk MODERATE Risk « HIGH Risk HIGH Risk

6–�0 LOW Risk MODERATE Risk « HIGH Risk HIGH Risk

��–�5 HIGH Risk HIGH Risk HIGH Risk HIGH Risk

>�5 HIGH Risk HIGH Risk HIGH Risk HIGH Risk

Levels of Risk During High-Wind EventsLOW Risk–Shelteringfromhighwindsisamatterofpreference.

MODERATE Risk–Sheltershouldbeconsideredforprotectionfromhighwinds.

HIGH Risk–Shelteristhepreferredmethodofprotectionfromhighwinds.


Alaska

Hurricane-Prone Region

Example:IfyourbuildingislocatedinNewSmyrnaBeach,Florida,youwouldseethatNewSmyrnaBeachisinanareashadedyellowontheFrequencyMap(previouspage).Accordingtothemap,thenumberoftornadoesper3,700squaremilesintheNewSmyrnaBeachareais1–5.OntheWindZoneMap(below),NewSmyrnaBeachiswithinthedarkorangearea.ThemapkeytellsyouthatNewSmyrnaBeachisinWindZoneIII.TheboxintheRiskTable(previouspage)wherethe1–5rowandtheZoneIIIcolumnmeetisshadeddarkblue,whichshowsthatthebuildingisinanareaofhighrisk.

Wind Zones in the United States

Can a Building Survive a Tornado? Yes!High-windshelterscanbedesignedandconstructedtoprotectoccupantsfromwindsandwindbornedebrisassociatedwithalltornadoes(EF0–EF5).Buildingsdesignedandconstructedabovebasiccoderequirements(aka“hardened”buildings),andnewerstructuresdesignedandconstructedtomodern,hazard-resistantcodescanresistthewindloadforcesfromweaktornadoes(EF1orweaker).Furthermore,evenwhenstrongertornadoesstrike,notalldamageisfromtherotatingvortexofthetornado.Muchofthedamageisfromstraight-linewindsrushingtowardandbeingpulledintothetornadoitself.Manynewerhomesdesignedandconstructedtomoderncodes,suchastheInternational Residential Codes(IRC2000Editionandnewer),withaloadpathtoresisthighwindforces(specifiedinbuildingcodesforhurricaneresistance)maysurvivewithoutstructuralfailure.Theprimarydamagetothesenewerhomesistothecladdingandexteriorsystems:roofcovering,roofdeck,exteriorwallsandwindows.Thistypeofdamagemaybepreventableonbuildingsthat

Notethatsomeareasoflowormoderaterisk,shownaspaleblueormediumblueontheRiskTable,arewithintheregionoftheUnitedStatesthatisalsosubjecttohurricanes(seeWindZoneMapbelow).Ifyouliveinthishurricane-proneregion,yourriskisconsideredhigheveniftheRiskTableonlyindicatesamoderateorlowrisk.

of 6Tornado Risks and Hazards in the Southeastern United States HSFEHQ-07-J-0006/April 2007

aredesignedandconstructedaccordingtotheIRC2000(ornewer)whenthebuildingexperiencesweakertornadoesandtheoutermostwindsfromstrongertornadoes.

Formostbuildinguses,itiseconomicallyimpracticaltodesigntheentirebuildingtoresisttornadoes.However,portionsofbuildingscanbedesignedasshelterstoprovideoccupantprotectionfromtornadoes.Forinformationondesigningshelterstoresistthestrongesttornadoesandhurricaneevents,seetheTornadoRecoveryAdvisorytitledStorm Shelters: Selecting Design Criteria.Forresidentialshelters,seetheTornadoRecoveryAdvisorytitledResidential Sheltering: In-Residence and Stand-Alone Shelters.

Forexistingbuildingsthatdonothavespecificallydesignedtornadosheltersoraccesstocommunitytornadoshelters,itisrecommendedthatbestavailablerefugeareasbeidentifiedinadvancebyaqualifiedarchitectorengineer.Forfurtherinformationonbestavailablerefugeareas,seeTornado Protection: Selecting Safe Areas in Buildings(FEMA431),November2003.

Weather RadiosAllindividualslivingorworkingintornado-proneareasshouldhaveaweatherradiowithintheirhomeorplaceofwork.Aweatherradioisparticularlyimportantforthoselivinginanareathatdoesnothavestormwarningsirens.

TheNationalOceanicandAtmosphericAdministration(NOAA)WeatherRadio(NWR)isanationwidenetworkofradiostationsbroadcastingcontinuousweatherinformationdirectlyfromanearbyNationalWeatherService(NWS)office.NWRbroadcastsNationalWeatherServicewarnings,watches,forecastsandotherhazardinformation24hoursaday,aswellaspost-eventinformationforalltypesofhazards,bothnaturalandtechnological.

NOAAWeatherRadiosareavailableatelectronicsstoresacrossthecountryandrangeincostfrom$25upto$100ormore,dependingonthequalityofthereceiverandnumberoffeatures.TheNWSdoesnotendorseanyparticularmakeormodelofreceiver.

Features to look for in a NOAA Weather Radio:

Themostdesirablefeatureisanalarmtone.Thisallowsyoutohavetheradioturnedonbutsilent,listeningforaspecialtonethatisbroadcastbeforewatchandwarningmessagesthatgiveimmediateinformationaboutalife-threateningsituation.

SpecificAreaMessageEncoding(SAME)technology,aNOAAWeatherRadiofeatureavailablesincethemid1990s,iscapableofprovidingdetailed,area-specificinformation.UnlikeotherNOAAWeatherRadios,theSAMEfeaturewillfilteroutalertsthatdonotaffectyourimmediatearea.

TheNOAAradioshouldoperateonbatteriesduringtimeswhenelectricalservicemaybeinterrupted.LookforradioswithanACadapterandbatterycompartment.

TheradioshouldbetunabletoallsevenNWRfrequencies.Forthelatestlistoffrequenciesandtransmitterlocations,checktheNOAAWeatherRadioWebsitehttp://www.weather.gov/nwr.

Thehearingandvisuallyimpairedcanreceivewatchesandwarningsbyconnectingweatherradioalarmstootherkindsofattention-gettingdevices,likestrobelights,pagers,bed-shakers,personalcomputers,andtextprinters.

AutomatedSpanishtranslationsystemsarebeingexaminedforuseontransmittersservingasignificantHispanicpopulationtobroadcastSpanishtranslationsofallemergencyweatherandnaturalhazardmessagesimmediatelyaftertheofficialEmergencyAlertSystem(EAS)warningisissued.FormoreinformationinSpanish,pleasevisittheNOAAWebsitehttp://www.weather.gov/nwr/indexsp.htm.

Other methods to receive forecasts, watches, and warnings directly from the NWS:

Tuneintoyourlocalradioandtelevisionstationsforthelatestweatherforecasts,watches,andwarnings.

NWSproductsandservicesarealsoavailableontheInternetathttp://www.weather.gov/nwr.DeliveryofdataacrosstheInternet,however,cannotbeguaranteedbecauseofpotentialinterruptionofservice.

Anotherlow-costmethodforreceivingtheNWS’sessentialinformationisavailableonawirelessdatasystemcalledtheEmergencyManagersWeatherInformationNetwork(EMWIN).Thissystempresentstheinformationdirectlyonyourhomeorofficecomputer.Usersmaysetvariousalarmstobealertedtoparticularinformation,whetherfortheirlocalareaoradjacentareas.Formoreinformation,pleasevisittheEMWINWebsitehttp://www.weather.gov/emwin/index.htm.


Useful Links and ResourcesTaking Shelter from the Storm: Building a Safe Room Inside Your House(FEMA320),March2004,2ndEdition

Design and Construction Guidance for Community Shelters (FEMA361),July2000

Tornado Protection: Selecting Safe Areas in Buildings(FEMA431),November2003

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Storm Shelters: Selecting Design Criteria FEBRUARY 2007 TORNADO RECOVERY ADVISORY FEMA DR 1679 RA2

Purpose and Intended Audience TheintendedaudienceforthisTornadoRecoveryAdvisory isanyoneinvolvedintheplanning,policy-making,design, construction,orapprovalofshelters,includingdesigners, emergencymanagers,publicofficials,policyordecisionmakers,buildingcodeofficials,andhomeorbuildingowners. HomeownersandrentersshouldalsorefertotheTornado RecoveryAdvisorytitledResidential Sheltering: In-Residence and Stand-Alone Shelter.Thepurposeofthisadvisoryisto identifythedifferenttypesofshelterdesignguidance,code requirements,andothercriteriathatpertaintothedesignand constructionofsheltersfortornadoesandhurricanes.Thereare variousstormsheltercriteria,eachofwhichoffersdifferentlevels ofprotectiontoitsshelteroccupants.


Howshelterconstructionisdifferentfromtypicalbuilding construction

Structuralsystems Windbornedebrisresistance

Designcriteriafordifferenttypesofshelters

Shelterconsiderations

Seethese2007TornadoRecovery Advisoriesforinformation abouttornadorisk,sheltering fromtornadoes,andimproving manufacturedhomesagainst damagefromhighwinds:

TornadoRisksandHazardsin theSoutheasternUnitedStates (TornadoRecoveryAdvisoryNo.1)

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

UnderstandingandImproving PerformanceofOlder ManufacturedHomesinHigh-Wind Events(TornadoRecoveryAdvisory No.4)

UnderstandingandImproving PerformanceofNewManufactured HomesinHigh-WindEvents (TornadoRecoveryAdvisoryNo.5)

Usefullinksandshelterresources

How Shelter Construction is Different from Typical Building Construction Ashelteristypicallyaninteriorroom,spacewithinabuilding,oranentirelyseparatebuilding,designedand constructedtoprotectitsoccupantsfromtornadoesorhurricanes.Sheltersareintendedtoprovideprotection againstbothwindforcesandtheimpactofwindbornedebris.Thelevelofoccupantprotectionprovidedby aspacespecificallydesignedasashelterisintendedtobemuchgreaterthantheprotectionprovidedby buildingsthatcomplywiththeminimumrequirementsofbuildingcodes.Themodelbuildingcodesdonot providedesignandconstructioncriteriaforlifesafetyforshelteringnordotheyprovidedesigncriteriafor tornadoes.

Shelterstypicallyfallintotwocategories:residentialsheltersandcommunity(non-residential)shelters.

Therearetwogeneraltypesofresidentialshelters:in-residence sheltersandshelterslocatedadjacentto,ornear,aresidence. Anin-residence shelter,alsocalleda“saferoom,”isasmall, speciallydesigned(“hardened”)room,suchasabathroomor closetthatisintendedtoprovideaplaceofrefugeforthepeople wholiveinthehouse.Anexternal residential shelterissimilar infunctionanddesign,butitisaseparatestructureinstalled outsidethehouse,eitheraboveorbelowground.Referalsoto theTornadoRecoveryAdvisorytitledResidential Sheltering: In-

Theterm“hardened”refersto specializeddesignandconstruction appliedtoaroomorbuildingto allowittoresistwindpressures andwindbornedebrisimpacts duringahigh-windeventandserve asashelter.

Residence and Stand-Alone Shelter.

Storm Shelters: Selecting Design Criteria HSFEHQ-07-J-0006/April 2007 Page � of 6

Acommunity shelterisintendedtoprovide protectionforalargenumberofpeople,anywhere fromapproximately12toasmanyasseveral hundredindividuals.Thesesheltersinclude notonlypublicsheltersbutprivatesheltersfor businessesandotherorganizations.

Structural Systems

Theprimarydifferenceinabuilding’sstructural systemwhendesignedforuseasashelter,rather thanforconventionaluse,isthemagnitudeofthe windforcesthatitisdesignedtowithstand.

Buildingsaredesignedtowithstandacertainwind speed(termed“design[basic]windspeed”)based onhistoricwindspeedsdocumentedfordifferentareasofthecountry.Thehighestdesignwindspeedused inconventionalconstructionisnearthecoastalareasoftheAtlanticandGulfCoastsandisintherangeof 140–150mph,3-secondgustinmostlocations.Bycontrast,thedesignwindspeedrecommendedbyFEMA1 forsheltersinthesesameareasisintherangeof200–250mph,3-secondgust;thisdesignwindspeedis intendedtoprovide“near-absoluteprotection.”

Windpressuresarecalculatedasafunctionofthesquareofthedesignwindspeed.Asaresult,the structuralsystemsofashelteraredesignedforforcesuptothreetimeshigherthanthoseusedfortypical buildingconstruction.Consequently,thestructuralsystemsofashelter(andtheconnectionsbetweenthem) areveryrobust.

Windborne Debris Resistance

Windbornedebris,commonlyreferredtoasmissiles,causesmanyoftheinjuriesandmuchofthedamage fromtornadoesandhurricanes.Windowsandtheglazinginexteriordoorsofconventionalbuildingsarenot requiredtoresistwindbornedebris,exceptforbuildingsinwindbornedebrisregions.2Impact-resistantglazing caneitherbelaminatedglass,polycarbonate,orshutters.TheASCE7missilecriteriaweredevelopedto minimizepropertydamageandimprovebuildingperformance;theywerenotdevelopedtoprotectoccupants.

Community storm shelter being constructed to FEMA 361 criteria in Wichita, Kansas.

Ifglazingispresentina tornadoshelter,itshould beprotectedbyaninterior-mountedshutterthatcanbe quicklyandeasilydeployed bytheshelteroccupants.

Toprovideoccupantprotection,thecriteriausedindesigningshelters includesubstantiallygreaterwindbornedebrisloads.

Theroofdeck,walls,anddoorsofconventionalconstructionarealso notrequiredbythebuildingcodetoresistwindbornedebris.However, theroofdeckandwallsaroundashelterspace,andthedoorsleading intoit,mustresistwindbornedebrisifthespaceinsideistoprovide occupantprotection.Additionalinformationregardingthedifferentlevels ofwindbornedebrisloadsisprovidedbelow.

Design Criteria for Different Types of Shelters Shelterswillprovidedifferentlevelsofprotectiondependinguponthedesigncriteriaused.Thelevelof protectionprovidedbyashelterisafunctionofthedesignwindspeed(andresultingwindpressure)usedin designingtheshelter,andofthewindbornedebrisloadcriteria.

Design wind speed and wind pressure criteria:Windpressurecriteriaaregivenbydifferentguides,codes andstandards.Windpressurecriteriaspecifyhowstrongthesheltermustbe.Thedesignwindspeedisthe majorfactorindeterminingthemagnitudeofthewindpressurethatthebuildingisdesignedtowithstand. InFEMA’sshelterpublications(seeUsefulLinksonpage3),recommendeddesignwindspeedsrange from160to250mph.The2006International Residential Codeandthe2006International Building Code, whichestablishtheminimumrequirementsforresidentialandotherbuildingconstruction,includedesign windspeedsrangingfrom90to150mphthroughoutmostofthecountry.Thetableonpages4–5provides acomparisonofshelterdesigncriteriaoptions.Thetableonpage6presentscomparativedatafortwo locationsusingthedesigncriteriapresentedonpages4–5.

1. FEMA361,Design and Construction Guidance for Community Shelters(July2000),availableonlineathttp://www.fema.gov/fima/fema361.shtm

2. ASCE7,AmericanSocietyofCivilEngineersStandard7,Minimum Design Loads for Buildings and Other Structures(2005)

Page 2 of 6 Storm Shelters: Selecting Design Criteria HSFEHQ-07-J-0006/April 2007

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Windborne debris load criteria: Thetableonpage3presentswindbornedebriscriteriagiveninvarious guides,codes,andstandards.Thetableshowsthedifferenttestmissilesandthecorrespondingmomentum theycarrywiththemastheystrikeashelter.Thefirstentriesonthistable(TornadoMissileTesting Requirements)aretheFEMAmissileguidanceforresidentialandcommunitysheltersthatprovidenearabsoluteprotection.

Tornado and Hurricane Windborne Debris Criteria Guidance, Code, or Standard

Criteria for the Design Missile Debris Test Speed

(mph) Large Missile Specimen Momentum at Impact (lbf s)

Tornado Missile Testing Requirements

FEMA320/FEMA361 100 15#2x4 68

InternationalCodeCouncil(ICC)Shelter Standard

100(maximum) 80(minimum)

15#2x4 15#2x4

68 55

Hurricane Missile Testing Requirements

FEMA320/FEMA361 100 15#2x4 68

ICCShelterStandard 102(maximum) 64(minimum)

9#2x4 9#2x4

42 26

FloridaStateEmergencyShelterProgram (SESP)Criteria

50(recommended) 34(EHPAminimum)

15#2x4 9#2x4

34 14

IBC/IRC2006,ASCE7-05,FloridaBuilding Code,ASTME1886/E1996

55 34

9#2x4 9#2x4

21 14

NOTES:

IBC/IRC–InternationalBuildingCode/InternationalResidentialCode

lbf-s–Pounds(force)seconds

Useful Links and Shelter Resources: Taking Shelter From the Storm: Building a Safe Room Inside Your House (FEMA320),FEMA,Washington,DC, SecondEdition,March2004.

Design and Construction Guidance for Community Shelters (FEMA361),FEMA,Washington,DC,July2000.

Tornado Protection: Selecting Refuge Areas in Buildings (FEMA431),FEMA,Washington,DC,November 2003.

Standard on the Design and Construction of Storm Shelters, International Code Council and the National Storm Shelter Association (ICC-500),(AnticipatedRelease)Late2007.

FEMA 320

FEMA 361

DRAFTFEMA 431

Storm Shelters: Selecting Design Criteria HSFEHQ-07-J-0006/April 2007 Page � of 6

Wind Design Coefficient Considerations�,� Debris Impact Criteria5 Remarks

FEMA �20:N/A–prescriptivedesignguidanceformaximumhazardFEMA �6�:UseFEMA361windspeedmapwithfourzones.CalculatepressuresusingASCE7methodsanduseI=1.0,Kd=1.0,ExposureC,notopographiceffects,GCpi=+/-0.55(thiswillaccountforatmosphericpressurechange[APC])

Testallshelterswiththerepresentativemissile:a15-lb2x4at100mph(horizontal)and67mph(vertical)

FEMA �20:Intentistoprovide“near-absoluteprotection.”Nocertificationisprovided.FEMA �6�:Intentistoprovide“near-absoluteprotection.”Shelteroperationsguidanceisprovided.Occupancyissuesaddressed.Wallsectiondetailsprovided.Nocertificationisprovided.

Tornado:UseFEMA361windspeedmap.CalculatepressuresusingASCE7methodsanduseI=1.0,Kd=1.0,Exposureasappropriate,notopographiceffects,GCpi=+/-0.55or+/-0.18+APCHurricane:UserevisedASCE7mapandmethodsanduseI=1.0,allotheritemsasperASCE7,noAPCconsiderationrequired.

Testshelterswithrepresentativemissile(missilespeeddependentonsitedesignwindspeed):Tornado:15-lb2x4at85–100mph(horizontal)and2/3ofthisspeed(vertical).Hurricane:9-lb2x4at68–105mph(horizontal)andalowerspeed(vertical)

Intentistoprovideastandardforthedesignandconstructionofhigh-windshelters.Willnotuseterm“near-absoluteprotection.”Occupancy,ventilation,anduseissuesarealsoaddressed.Shelteroperationsguidanceisprovidedinthecommentaryonly(commentaryisaseparatedocument—notaconsensusdocument).

Recommendsthatdesigneradd40mphtobasicwindspeedidentifiedonmap,ExposureC,I=1.15,Kd=0.85,GCpiasrequiredbydesign(typically+/-0.18),butrecommends+/-0.55fortornadoshelteruses

Inwindbornedebrisregion(120mph+):Small–peagravel;Large–9-lb2x4at34mph(horizontal),upto60feetabovegrade,butrecommends15-lb2x4at50mph(horizontal)

Thebuilding,oraportionofabuilding,isdefinedasanessentialfacilityandasashelter.Designerisrequiredtosubmitsigned/sealedstatementtobuildingdepartmentandStateofficesstatingthestructurehasbeendesignedasashelter(EHPAplusaddedrecommendedcriteria).

UsebasicwindspeedatsiteasidentifiedonFBCwindspeedmap,useexposureatsite,useI=1.15,Kd=0.85,GCpiasrequiredbydesign(typically+/-0.18)

Inwindbornedebrisregion(120mph+):Small–peagravel;Large–9-lb2x4at34mph(horizontal),upto60feetabovegrade

ThebuildingoraportionofabuildingisdefinedasanessentialfacilityandasanEHPA.Designerisrequiredtosubmitsigned/sealedstatementtobuildingdepartmentandStateofficesstatingthestructurehasbeendesignedasanEHPA.

Basedonregionalhazards,recommendationsareprovidedtoimproveandstrengthentheloadpathandtheperformanceofthebuildingexterior

Windowandglazingprotectionisrecommendedformosthurricane-proneareas,notjustareaswithabasicwindspeedof120mphandgreater

Thisprogramprovidesdesignandconstructionguidancetoimprovebuildingperformanceforhigh-windevents.Compliancewilllikelyimprovebuildingperformancebutdoesnotimplythatthebuildingissafeorthatitisappropriatetouseasashelter.

Methodisbasisofmostwindpressurecalculationmethods.Allitemsindesignprocessaresite-specific.UseI=1.15forcriticalandessentialfacilities

Inwindbornedebrisregion(120mph+):Small–peagravel;Large–9-lb2x4at34mph(horizontal),upto60feetabovegrade.Note:2006IBCrequiresthe9-lb2x4(large)missiletobetestedat55mphforcriticalandessentialfacilities

Coderequiresincreaseddesignparametersonlyforbuildingsdesignatedascriticaloressentialfacilities.

None None Providesguidanceonhowtoselectbuildingsandareasofabuildingforuseasahigh-windshelterorrefugearea.Doesnotprovideorrequireatechnicalassessmentoftheproposedshelterfacility.

Typicallytheseoldercodesprovidedahurricaneregionalfactorfordesignwindspeeds,butlittleattentionwaspaidtocomponentsandcladding

Notrequiredforallbuildings.Whererequired,theStandardBuildingCode6developedandrecommendeddebrisimpactstandardsforuseinhurricane-proneregions

Thesecodesspecifiedlimitedhazard-resistantrequirements.SomeguidancewasprovidedwithSSTD10fromSBCCIforthedesignandconstructionofbuildingsinhigh-windandhurricane-proneregions.Buildingsconstructedtotheseearlycodeswerenotrequiredtohavestructuralsystemscapableofresistingwindloads.

None None Bestavailablerefugeareasshouldbeidentifiedinallbuildingswithoutshelters.FEMA431,Tornado Protection: Selecting Refuge Areas in Buildings,providesguidancetohelpidentifythebestavailablerefugeareasinexistingbuildings.Becausebestavailablerefugeareasarenotspecificallydesignedasshelters,theiroccupantsmaybeinjuredorkilledduringatornadoorhurricane.

Wind Shelter Design and Construction Codes, Standards, Guidance Comparison Table�

Title or Name of Document Code, Reg, Standard, or Statute? Wind

Hazard Wind Map

FEMA Shelter Publications: FEMA �20Taking Shelter From the Storm: Building a Safe Room Inside Your House(1999) FEMA �6�Design and Construction Guidance for Community Shelters(2000)

FEMAguidancedocument,notacodeor standard.“BestPractice”forhigh-wind shelters

Tornadoand Hurricane

FEMA �20:Hazardmap,butwind speedsnotusedfordesign FEMA �6�:Mapwithfourwind speedzonesfordesign(windmri2is 10,000–100,000years).Thismap isoftenreferredtoasthe“FEMA 361map”

International Code Council/National Storm Shelter Association (ICC/NSSA) High Wind Shelter Standard (ICC-500) –currentlyindevelopment,tentatively availableforadoptioninJanuary2008.

Consensusstandardforshelterdesign andconstruction,availableforadoption inJanuary2008.Tobeincorporatedby referenceintothe2009IBCandIRC.


Tornado:UsesFEMA361map Hurricane:UsesrevisedASCE7 mapwithcontoursat10,000year mriwithminimumshelterdesign windspeedof160mph,maximum approximately240mph

Florida State Emergency Shelter Program (SESP)– FloridaInterpretationoftheAmericanRedCross(ARC) 4496Guidance.Note:sheltersinthiscategorywill rangefromEnhancedHurricaneProtectionArea(EHPA) recommendeddesignlevels,showninthisrow,tothe coderequirementlevels(nextrow),totheARC4496 requirements(seebelow).

GuidanceintheFBC“recommending” above-coderequirementsforEHPAs.See alsoAppendixGoftheStateEmergency ShelterProgram(SESP)reportforthe detaileddesignguidance.


FloridaBuildingCode(FBC)map, basedonASCE7(mapsbasically equivalent);mriis50–100years incoastalareasandadjustedwith importancefactor

Florida Building Code (FBC) EHPAs–code requirementsforpublic“shelters”(FBCSection 423.25).

StatewidecoderequirementsforEHPAs Hurricane FBCmap,basedonASCE7(maps basicallyequivalent);mriis50–100 yearsincoastalareasandadjusted withimportancefactor

Institute for Business and Home Safety (IBHS) Fortified Home Program–intendedasguidance toimprovetheperformanceofresidentialbuildings duringnaturalhazardevents,includinghigh-wind events–notconsideredadequateforsheltering.

Guidanceprovidedtoimproveperformance ofregular(non-shelter)buildingsinhigh winds


ASCE7ormodernStatebuilding codemap

FBC 2000 and later, International Building Code (IBC)/International Residential Code (IRC) 2000 and later/ASCE 7-98andlater.

Buildingcodeanddesignstandardsfor regular(non-shelter)buildings.Some additionalguidanceisprovidedin commentary.

Hurricane ASCEhasitsownwindspeedmap basedonhistoricalandprobabilistic data;mriis50–100yearsincoastal areasandadjustedwithimportance factor

American Red Cross (ARC ��96)Standards for Hurricane Evacuation Shelter Selection.

Guidanceforidentifyingbuildingstouseas hurricaneevacuationshelters

Hurricane None

Pre-2000 Building Codes Buildingcodeanddesignstandardsfor regular(non-shelter)buildings

Hurricane Eachoftheoldercodesusedtheir ownpublishedwindcontourmaps

Areas of Refuge/Last Resort GuidancefromFEMAandothersfor selectingbest-availablerefugeareas


None

NOTES:

1. Thewindshelterguidanceandrequirementsshownherearepresentedfromhighesttoleastamountofprotectionprovided.

2.Meanrecurrenceintervals(mri)forwindspeedsmapsareidentifiedbythecodeorstandardthatdevelopedthemap.Typically,themrifornonshelterconstructioninnon-hurricane-proneareasis50yearsandinhurricane-proneregions,approximately100years.

Page � of 6 Storm Shelters: Selecting Design Criteria HSFEHQ-07-J-0006/April 2007

Title or Name of Document Code, Reg, Standard, or Statute?Wind

Hazard Wind Map

FEMA Shelter Publications:FEMA �20Taking Shelter From the Storm: Building a Safe Room Inside Your House(1999)FEMA �6�Design and Construction Guidance for Community Shelters(2000)

FEMAguidancedocument,notacodeorstandard.“BestPractice”forhigh-windshelters

TornadoandHurricane

FEMA �20:Hazardmap,butwindspeedsnotusedfordesignFEMA �6�:Mapwithfourwindspeedzonesfordesign(windmri2is10,000–100,000years).Thismapisoftenreferredtoasthe“FEMA361map”

International Code Council/National Storm Shelter Association (ICC/NSSA) High Wind Shelter Standard (ICC-500) –currentlyindevelopment,tentativelyavailableforadoptioninJanuary2008.

Consensusstandardforshelterdesignandconstruction,availableforadoptioninJanuary2008.Tobeincorporatedbyreferenceintothe2009IBCandIRC.

TornadoandHurricane

Tornado:UsesFEMA361mapHurricane:UsesrevisedASCE7mapwithcontoursat10,000yearmriwithminimumshelterdesignwindspeedof160mph,maximumapproximately240mph

Florida State Emergency Shelter Program (SESP)–FloridaInterpretationoftheAmericanRedCross(ARC)4496Guidance.Note:sheltersinthiscategorywillrangefromEnhancedHurricaneProtectionArea(EHPA)recommendeddesignlevels,showninthisrow,tothecoderequirementlevels(nextrow),totheARC4496requirements(seebelow).

GuidanceintheFBC“recommending”above-coderequirementsforEHPAs.SeealsoAppendixGoftheStateEmergencyShelterProgram(SESP)reportforthedetaileddesignguidance.

TornadoandHurricane

FloridaBuildingCode(FBC)map,basedonASCE7(mapsbasicallyequivalent);mriis50–100yearsincoastalareasandadjustedwithimportancefactor

Florida Building Code (FBC) EHPAs–coderequirementsforpublic“shelters”(FBCSection423.25).

StatewidecoderequirementsforEHPAs Hurricane FBCmap,basedonASCE7(mapsbasicallyequivalent);mriis50–100yearsincoastalareasandadjustedwithimportancefactor

Institute for Business and Home Safety (IBHS) Fortified Home Program–intendedasguidancetoimprovetheperformanceofresidentialbuildingsduringnaturalhazardevents,includinghigh-windevents–notconsideredadequateforsheltering.

Guidanceprovidedtoimproveperformanceofregular(non-shelter)buildingsinhighwinds

TornadoandHurricane

ASCE7ormodernStatebuildingcodemap

FBC 2000 and later, International Building Code (IBC)/International Residential Code (IRC) 2000 and later/ASCE 7-98andlater.

Buildingcodeanddesignstandardsforregular(non-shelter)buildings.Someadditionalguidanceisprovidedincommentary.

Hurricane ASCEhasitsownwindspeedmapbasedonhistoricalandprobabilisticdata;mriis50–100yearsincoastalareasandadjustedwithimportancefactor

American Red Cross (ARC ��96)Standards for Hurricane Evacuation Shelter Selection.

Guidanceforidentifyingbuildingstouseashurricaneevacuationshelters

Hurricane None

Pre-2000 Building Codes Buildingcodeanddesignstandardsforregular(non-shelter)buildings

Hurricane Eachoftheoldercodesusedtheirownpublishedwindcontourmaps

Areas of Refuge/Last Resort GuidancefromFEMAandothersforselectingbest-availablerefugeareas

TornadoandHurricane

None

Part2oftable(continuedfrompage4)

Wind Design Coefficient Considerations�,� Debris Impact Criteria5 Remarks

FEMA �20:N/A–prescriptivedesign guidanceformaximumhazard FEMA �6�:UseFEMA361windspeed mapwithfourzones.Calculatepressures usingASCE7methodsanduseI=1.0, Kd=1.0,ExposureC,notopographic effects,GCpi=+/-0.55(thiswillaccountfor atmosphericpressurechange[APC])

Testallshelterswiththerepresentative missile:a15-lb2x4at100mph (horizontal)and67mph(vertical)

FEMA �20:Intentistoprovide“near-absoluteprotection.”No certificationisprovided. FEMA �6�:Intentistoprovide“near-absoluteprotection.”Shelter operationsguidanceisprovided.Occupancyissuesaddressed. Wallsectiondetailsprovided.Nocertificationisprovided.

Tornado:UseFEMA361windspeed map.CalculatepressuresusingASCE7 methodsanduseI=1.0,Kd=1.0,Exposure asappropriate,notopographiceffects, GCpi=+/-0.55or+/-0.18+APC Hurricane:UserevisedASCE7mapand methodsanduseI=1.0,allotheritemsas perASCE7,noAPCconsiderationrequired.

Testshelterswithrepresentative missile(missilespeeddependenton sitedesignwindspeed):Tornado:15-lb 2x4at85–100mph(horizontal)and 2/3ofthisspeed(vertical).Hurricane: 9-lb2x4at68–105mph(horizontal) andalowerspeed(vertical)

Intentistoprovideastandardforthedesignandconstructionof high-windshelters.Willnotuseterm“near-absoluteprotection.” Occupancy,ventilation,anduseissuesarealsoaddressed. Shelteroperationsguidanceisprovidedinthecommentary only(commentaryisaseparatedocument—notaconsensus document).

Recommendsthatdesigneradd40mph tobasicwindspeedidentifiedonmap, ExposureC,I=1.15,Kd=0.85,GCpias requiredbydesign(typically+/-0.18),but recommends+/-0.55fortornadoshelter uses

Inwindbornedebrisregion(120 mph+):Small–peagravel;Large–9-lb 2x4at34mph(horizontal),upto60 feetabovegrade,butrecommends15lb2x4at50mph(horizontal)

Thebuilding,oraportionofabuilding,isdefinedasanessential facilityandasashelter.Designerisrequiredtosubmitsigned/ sealedstatementtobuildingdepartmentandStateofficesstating thestructurehasbeendesignedasashelter(EHPAplusadded recommendedcriteria).

Usebasicwindspeedatsiteasidentified onFBCwindspeedmap,useexposureat site,useI=1.15,Kd=0.85,GCpiasrequired bydesign(typically+/-0.18)

Inwindbornedebrisregion(120 mph+):Small–peagravel;Large–9-lb 2x4at34mph(horizontal),upto60 feetabovegrade

Thebuildingoraportionofabuildingisdefinedasanessential facilityandasanEHPA.Designerisrequiredtosubmitsigned/ sealedstatementtobuildingdepartmentandStateofficesstating thestructurehasbeendesignedasanEHPA.

Basedonregionalhazards, recommendationsareprovidedtoimprove andstrengthentheloadpathandthe performanceofthebuildingexterior

Windowandglazingprotectionis recommendedformosthurricane-prone areas,notjustareaswithabasicwind speedof120mphandgreater

Thisprogramprovidesdesignandconstructionguidanceto improvebuildingperformanceforhigh-windevents.Compliance willlikelyimprovebuildingperformancebutdoesnotimplythatthe buildingissafeorthatitisappropriatetouseasashelter.

Methodisbasisofmostwindpressure calculationmethods.Allitemsindesign processaresite-specific.UseI=1.15for criticalandessentialfacilities

Inwindbornedebrisregion(120 mph+):Small–peagravel;Large–9-lb 2x4at34mph(horizontal),upto60 feetabovegrade. Note:2006IBCrequiresthe9-lb2x4 (large)missiletobetestedat55mph forcriticalandessentialfacilities

Coderequiresincreaseddesignparametersonlyforbuildings designatedascriticaloressentialfacilities.

None None Providesguidanceonhowtoselectbuildingsandareasofabuilding foruseasahigh-windshelterorrefugearea.Doesnotprovideor requireatechnicalassessmentoftheproposedshelterfacility.

Typicallytheseoldercodesprovideda hurricaneregionalfactorfordesignwind speeds,butlittleattentionwaspaidto componentsandcladding

Notrequiredforallbuildings.Where required,theStandardBuildingCode6 developedandrecommendeddebris impactstandardsforuseinhurricaneproneregions

Thesecodesspecifiedlimitedhazard-resistantrequirements. SomeguidancewasprovidedwithSSTD10fromSBCCIforthe designandconstructionofbuildingsinhigh-windandhurricaneproneregions.Buildingsconstructedtotheseearlycodeswerenot requiredtohavestructuralsystemscapableofresistingwindloads.

None None Bestavailablerefugeareasshouldbeidentifiedinallbuildings withoutshelters.FEMA431,Tornado Protection: Selecting Refuge Areas in Buildings,providesguidancetohelpidentifythebest availablerefugeareasinexistingbuildings.Becausebestavailable refugeareasarenotspecificallydesignedasshelters,their occupantsmaybeinjuredorkilledduringatornadoorhurricane.

NOTES(continued):

3. ASCE7-05Building Design Loads for Buildings and Other Structures(2005)istheloaddeterminationstandardreferencedbythe modelbuildingcodes.Thewinddesignproceduresusedforanysheltertypeinthistableuseoneofthewinddesignmethodsas specifiedinASCE7-05,butwithchangestocertaindesigncoefficientsthatareidentifiedbythedifferentcodes,standards,or guidancesummarizedinthistable.

4. FromASCE7method:I=importancefactor;Kd=winddirectionalityfactor;GCpi=internalpressurecofficient

5. Roofdeck,walls,doors,openings,andopeningprotectionsystemsmustallbetestedtoshowresistancetothedesignmissileforthe FEMA,ICC,andFLEHPAcriteria.

6. FromtheSouthernBuildingCodeCongressInternational,Inc.(SBCCI).

Storm Shelters: Selecting Design Criteria HSFEHQ-07-J-0006/April 2007 Page 5 of 6

Thetablebelowshowscomparativedatafortwolocationsforthedesigncriteriapresentedintheprevious table.Wherenoguidanceisprovidedforshelteringorbasicconstruction,“N/A”(notapplicable)isstated. Wheretherequirementisnotrequired,“Notrequired”isstated.

Design Criteria Comparison Shelter Design Standard,

Code, or Document Data� Example Location #�:

Miami, FL Example Location #2:

Atlanta, GA

FEMA320/361 Designwindspeed 200mph 200mph

Pressureonwindwardwall 107psf2 107psf

Pressureonroofsection 257psf(suction) 257psf(suction)

Testmissilemomentumatimpact 68lbf-s2 68lbf-s

ICC-500(pending1/08) Designwindspeed 200mph(tornado) 225mph(hurricane)

200mph(tornado) 160mph(hurricane)

Pressureonwindwardwall 107psf(tornado) 136psf(hurricane)

107psf(tornado) 69psf(hurricane)

Pressureonroofsection 257psf(tornado,suction) 325psf(hurricane,suction)

257psf(tornado,suction) 202psf(hurricane,suction)

Testmissilemomentumatimpact 68lbf-s(tornado) 42-26lbf-s(hurricane)

68lbf-s(tornado) 42-26lbf-s(hurricane)

FBCEHPA/SESP (using+40mph recommendation)

Designwindspeed 186mph 130mph

Pressureonwindwardwall 91psf 44psf


Testmissilemomentumatimpact 34lbf-s 34lbf-s

FBCEHPA Designwindspeed 146mph N/A

Pressureonwindwardwall 39psf N/A

Pressureonroofsection 117psf(suction) N/A

Testmissilemomentumatimpact 14lbf-s N/A

IBHS Designwindspeed 150mph 90mph



Testmissilemomentumatimpact 14lbf-s 14lbf-s

ASCE7-05/IBC2006 (ASTME1996)

Designwindspeed 150mph 90mph



Testmissilemomentumatimpact 14lbf-s Notrequired

ARC4496 Designwindspeed N/A N/A

Pressureonwindwardwall N/A N/A

Pressureonroofsection N/A N/A

Testmissilemomentumatimpact N/A N/A

Pre-2000BuildingCodes Designwindspeed 140mphandless 90mphandless

Pressureonwindwardwall <40psf(varies) <15psf(varies)

Pressureonroofsection <120psf(varies) <45psf(varies)

Testmissilemomentumatimpact Notrequiredbyallcodes Notrequired

AreasofLastResort Designwindspeed Unknown Unknown

Pressureonwindwardwall Unknown Unknown

Pressureonroofsection Unknown Unknown

Testmissilemomentumatimpact Notrequired Notrequired NOTES: 1. Windpressureswerecalculatedbasedona40-footx40-footsquarebuilding,witha10-footeaveheightanda10-degreeroofpitch. 2. psf–Poundspersquarefoot;lbf-s–Pounds(force)seconds

Page 6 of 6 Storm Shelters: Selecting Design Criteria HSFEHQ-07-J-0006/April 2007

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Residential Sheltering: In-Residence and Stand-Alone Shelters FEBRUARY 2007 TORNADO RECOVERY ADVISORY FEMA DR 1679 RA3

Intended Audience and Purpose Thepurposeofthisadvisoryistoalerthomeowners, renters,apartmentbuildingowners,and manufacturedhomeparkownersabouttheconcept ofin-residenceandstand-alonestormshelters.


Considerashelterforyourhome

In-residenceshelterconstructionandretrofitting options

Shelteringoptionsforwhenyoucan’tplacea shelterwithinyourhome

Areasoflastresortforthoseresidentsthatdon’t haveaccesstoashelter

Emergencyplanning

Seethese2007TornadoRecoveryAdvisoriesfor informationabouttornadorisk,shelteringfrom tornadoes,andimprovingmanufacturedhomes againstdamagefromhighwinds:

TornadoRisksandHazardsinthe SoutheasternUnitedStates(TornadoRecovery AdvisoryNo.1)

StormShelters:SelectingDesignCriteria (TornadoRecoveryAdvisoryNo.2)

UnderstandingandImprovingPerformance ofOlderManufacturedHomesinHigh-Wind Events(TornadoRecoveryAdvisoryNo.4)

UnderstandingandImprovingPerformanceof NewManufacturedHomesinHigh-WindEvents (TornadoRecoveryAdvisoryNo.5)

Consider a Shelter for Your Home Thepurposeofhavingashelter(alsoknownasa“saferoom”)inornearyourhomeistoprotectyouand yourfamilyfrominjuryordeathcausedbyextremewinds.Sheltersareintendedtoallowoccupantstosurvive tornadoesandhurricaneswithlittleornoinjury.Todetermineyourexposuretotornadoes,refertoFEMA320, Taking Shelter From the Storm: Building a Safe Room Inside Your House(SecondEdition,March2004).1This publicationprovidesinformationthatcanhelpyoudecidewhetherornottoconstructasheltertoprotectyou andyourfamilyfrominjuryordeathduringatornado orhurricane.Additionalinformationisprovidedinthe TornadoRecoveryAdvisorytitledTornado Risks and Hazards in the Southeastern United States.

Afterdeterminingthatyouliveinatornado-or hurricane-proneregion,itisimportanttounderstand therisks.Mosthomes,evennewonesconstructed accordingtocurrentbuildingcodes,donotprovide adequateprotectionforoccupantsseekingrefuge fromtornadoes.Atornadoorhurricanecancause windandwindbornedebrisloadsonyourhousethat aremuchgreaterthanthoseonwhichbuildingcode requirementsarebased.Onlyspeciallydesignedand constructedshelters,whicharevoluntarilybuiltabove theminimumcoderequirements,offeroccupant protectionduringatornadoorstronghurricane.

Itisalsoimportanttorememberthatshelters offeringprotectionagainsthigh-windevents shouldnotbeplacedwherefloodwatershave thepotentialtoendangeroccupantswithin theshelter.Ifyourshelterislocatedwhere coastalorriverinefloodingmayoccurduring hurricanes,itshouldnotbeoccupiedduringa hurricane.However,occupyingsuchashelter duringatornadomaybeacceptable,provided thattheshelterislocatedwhereitwillnotbe floodedbyrainsassociatedwithotherstorm andtornadoevents.Consultyourlocalbuilding officialorlocalNationalFloodInsuranceProgram representativetodeterminewhetheryour home,oraproposedstand-alonesheltersite,is susceptibletoriverineorcoastalflooding.

1. FEMA320isavailableonlineathttp://www.fema.gov/plan/prevent/saferoom/fema320.shtm.Hardcopiesmaybeobtainedatnocostbycalling 800-480-2520.

Residential Sheltering: In-Residence and Stand-Alone Shelters HSFEHQ-07-J-0006/April 2007 Page � of 4

In-Residence Shelter Construction and Retrofitting Options Constructingashelterwithin yourhomeputsitascloseas possibletoyourfamily.Ashelter maybeinstalledduringthe initialconstructionofahome, orretrofittedafterward.Aslong asthedesignandconstruction requirementsandguidance arefollowed,thesamelevelof protectionisprovidedbyeither typeofshelter.

New Construction

FEMA320providesdetailed drawingsandspecifications thatcanbeusedbyabuilder/ contractortoconstructashelterin yourhome.Thedesignsprovided areforsheltersconstructedof wood,masonry,orconcrete.Allof themaredesignedtoresist250mph(3-secondgust)windspeeds andimpactsfromwindborne debris.Pre-fabricatedshelters arealsoavailableforinstallation byabuilder/contractorwhenfirst buildingyourhome.Thebasiccost todesignandconstructashelter duringtheconstructionofanew houseisapproximately$6,000, withlarger,morerefined,andmore comfortabledesignscostingmore than$15,000.

Itisrelativelyeasyandcosteffectivetoaddashelterwhenfirst buildingyourhome.Forexample, whenthehomeisconstructed withexteriorwallsmadefrom concretemasonryunits(CMU,also commonlyknownas“concrete block,”seesketchthispage), theprotectionlevelinFEMA 320canbeachievedbyslightly modifyingtheexteriorwallsat theshelterspacewithadditional steelreinforcementandgrout. Theshelteriseasilycompletedby addinginteriorwallsconstructed ofreinforcedCMU,aconcreteroof deckovertheshelter,andaspecial shelterdoor,asshownunder constructioninbottomphotograph.

CMU was used for the exterior walls at this house under construction (New Smyrna Beach, FL).

Sketch of floor plan showing location of shelter area in house.

View of an in-residence shelter under construction. Steel reinforced and fully grouted CMU surround the shelter space (New Smyrna Beach, FL).

Page 2 of 4 Residential Sheltering: In-Residence and Stand-Alone Shelters HSFEHQ-07-J-0006/April 2007

Retrofitting Existing Houses

FEMA320providesgeneralguidanceforretrofittingahousewithashelter.Buildingashelterinanexisting housewilltypicallycost20percentmorethanbuildingthesameshelterinanewhousewhileunder construction.Becausetheshelterisbeingusedforlifesafety,andbecauseyourhomemightbeexposed towindloadsanddebrisimpactsitwasnotdesignedtoresist,anarchitectorengineer(A/E)shouldbe employedtoaddressspecialstructuralrequirements,evenifinclusionofanA/Einsuchaprojectisnot requiredbythelocalbuildingdepartment.

Recommendations for Sheltering When You Cannot Place a Shelter Within Your Home Manyreasonsmaypreventahomeownerorrenterfrominstallingorconstructingashelterwithintheirhome. Thesereasonsmayinclude:lackofpermission(theresidentdoesnotownthehomeordoesnothave rightstomodifyorchangethehome),lackofavailablespace,orlackoftechnicaloreconomicpracticality. Nonetheless,homeownersorrentersmaywanttoproceedwithinstallingashelter.Stand-aloneshelterscan bedesignedandconstructedoutsideofaresidence.Theseshelterscanprovidethesamelevelofprotection againsthighwindsandwindbornedebrisasdothein-residenceshelters.

Small Stand-Alone Shelters

Somesite-builthomes,andmost manufacturedhomes,donot lendthemselvestothestructural modificationsandretrofitting requiredtoinstallorconstruct anin-residenceshelter.Inthese instances,astand-aloneshelter maybeconstructed(eitherabovegrade,partiallyabove-grade[see photographtoright],orbelow grade)neartheresidence.Small stand-aloneshelterscanbe constructedtoaccommodatethe occupantsofonehouse,afew houses,orasmallapartment building.Thisphoto,fromWichita, KS,showshowamanufactured homecommunityprovidedsmall, pre-fabricatedsheltersasa refugefortheresidents.Each shelterprovidessafetyforseveral homesinthecommunity.

Community Shelters

Acommunitysheltercanbe constructedtoaccommodate theoccupantsofseveral apartmentsorhomes(sitebuiltormanufacturedhomes, seephotographtoright).For informationaboutcommunity shelters,refertotheTornado RecoveryAdvisorytitledStorm Shelters: Selecting Design Criteria. Manydifferenttypesofshelters canbedesignedandconstructed tomeettheneedsoflargegroups ofresidents.Asheltermaybe asingle-usebuilding,oritmay beamulti-usebuilding,such

View of a pre-fabricated shelter that serves a few manufactured homes (Wichita, KS).

View of a partially below-grade community shelter at a manufactured home community (Wichita, KS).

Residential Sheltering: In-Residence and Stand-Alone Shelters HSFEHQ-07-J-0006/April 2007 Page � of 4

asaclubhouse(atcommunitypools,golfcourses,etc.),schoolbuilding, orrecreationcenter.Selectingtherighttypeofshelterwillbeacollective decisionmadebytheresidents,fundingagencies,andpropertyownersand managers.Forinformationoncommunitysheltersforlargerpopulations, includingplanningandoperationalissues,seeFEMA361,Design and Construction Guidance for Community Shelters(2000).2

Areas of Last Resort

Forfurtherinformation aboutpre-fabricatedand stand-aloneshelters, contacttheNational StormShelterAssociation (http://www.nssa.cc)

Occupantsofdwellingsthatdo nothavein-residenceshelters, oraccesstostand-aloneor communityshelters,should identifythebestavailablerefuge areawithintheirhomebefore anemergencyhappens.When peopleidentifyandtakerefuge inthebestavailablespacewithin abuilding,theyarelesslikelyto beinjuredorkilled.However,it isimportanttorememberthat “bestavailablerefugeareas” arenotspecificallydesignedas shelters,sooccupantsmaybe injuredorkilledduringatornado orhurricaneevent.

Thefollowingcriteriashould beusedinidentifyingthebest availablerefugeareainyour home:

Choosethelowestfloorof theresidence(abasementis preferable,orfirstfloorifthere isnobasement).

Chooseasmallinteriorroom withoutwindows(i.e.,noneof theroom’swallsisanexterior wall),suchasabathroomor closet,preferablywithonlyone door.

Choosearoomlocatedaway frommasonrychimneys,trees, orpowerpoles.

Keeptheroomrelativelyfreeofcluttersoyouandtheotherresidentscanenterandremainintheroomfor uptoseveralhours.

Emergency Supply Kits and Weather Radios FEMA320providesinformationtouseinpreparingaFamilyEmergencyPlanandanEmergencySupplyKitfor theshelter.Further,allindividualslivingorworkingintornado-proneareasshouldhaveaweatherradiowithin theirhomeorplaceofwork.Formoreinformationaboutweatherradios,seetheTornadoRecoveryAdvisory titledTornado Risks and Hazards in the Southeastern United States.

View of remnants of an interior room of a house that survived a strong tornado.

Avoid selecting a refuge area that is near a masonry chimney (Moore, OK).

2. FEMA361isavailableonlineathttp://www.fema.gov/fima/fema361.shtm.

Page 4 of 4 Residential Sheltering: In-Residence and Stand-Alone Shelters HSFEHQ-07-J-0006/April 2007

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Understanding and Improving Performance of Older Manufactured Homes During High-Wind Events FEBRUARY 2007 TORNADO RECOVERY ADVISORY FEMA DR 1679 RA4

Purpose and Intended Audience High-windeventscandamageordestroymanufacturedhomes.While revisionstomanufacturedhomestandardscontinuetoimprove performance,oldermanufacturedhomesremaininuseandare particularlyvulnerabletohighwinds.Theseriesoftornadoesthat struckCentralFloridaonFebruary2,2007isbutonehigh-windevent thathasshownthevulnerabilityofoldermanufacturedhomes.The tornadoesdestroyednumerousoldermanufacturedhomesandforced numerousothersofftheirfoundations.ThepurposeofthisTornado RecoveryAdvisoryistoprovideguidanceonmethodstoreducewind damagetomanufacturedhomesconstructedbeforeJuly13,1994. Guidanceforreducingdamagetomanufacturedhomesconstructed afterJuly13,1994iscontainedintheTornadoRecoveryAdvisorytitled Understanding & Improving Performance of New Manufactured Homes During High-Wind Events.

Thisrecoveryadvisoryisdirectedtoownersof“older”(pre-1994) manufacturedhomes.Buildingofficials,manufacturedhomeinstallers andcontractors,andoperatorsofmanufacturedhomecommunities mayalsofinditinformative.


Manufacturedhomeages

Vulnerabilitiesofoldermanufacturedhomestohigh-windevents

Recommendations1

Manufactured Home Ages

Seethese2007Tornado RecoveryAdvisoriesfor informationabouttornado risk,shelteringfrom tornadoes,andimproving manufacturedhomes againstdamagefromhigh winds:

TornadoRisksand Hazardsinthe SoutheasternUnited States(TornadoRecovery AdvisoryNo.1)

StormShelters:Selecting DesignCriteria(Tornado RecoveryAdvisoryNo.2)

ResidentialSheltering: In-ResidenceandStand-AloneShelters(Tornado RecoveryAdvisoryNo.3)

Understandingand ImprovingPerformance ofNewManufactured HomesDuringHigh-Wind Events(TornadoRecovery AdvisoryNo.5)

Althoughtherearenostrictdefinitionsof“older”and“new” manufacturedhomes,thefollowingdescriptions,whicharebasedon theevolutionofmanufacturedhomeconstructionstandards,areuseful.

“Older” Manufactured Homes

Thiscategoryincludes“pre-code”homesand“earlycode”homes.Somemanufacturedhomesconsidered “older”mayberelativelynewfromanexpectedservicelifestandpoint,butarestilloldfromawindresistance standpoint.Forthisrecoveryadvisory,anymanufacturedhomeconstructedbeforeJuly13,1994,is consideredanoldermanufacturedhome.

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

1. Actionsrecommendedbythisrecoveryadvisorycanreducedamagetomanufacturedhomesduringhigh-windevents.Theactionswillnot,however, strengthenoldermanufacturedhomesenoughtoallowoccupantstosafelyremainintheirhomesduringtornadoesorhurricanes.Whenadvisedby localorStateauthorities,occupantsofmanufacturedhomesshouldfindsuitableshelterwhentornadoesorhurricanesthreaten.

Understanding and Improving Performance of Older Manufactured Homes During High-Wind Events HSFEHQ-07-J-0007/April 2007 Page � of 7

housingwasessentiallyunregulatedandwidevariationsinconstructionqualityandstrengthexisted.Precodemanufacturedhomeswereoftencalledtrailersormobilehomesbecausetheywereintendedtobe movedfromplacetoplace.

Early Code Manufactured Homes:ThesearehomesbuiltafterJune15,1976(andbeforeJuly13,1994) whentheManufacturedHomeConstructionandSafetyStandards(MHCSS),developedbyHUD,firstwent intoeffect.After1976,homesbecameknownas “manufacturedhousing.”TheMHCSSspecified minimumwindpressuresthatmanufactured homesmustbedesignedtoresist.Italso containedgeneralcriteriaforanchoringhomesto resistwindforces.Thewindpressuresrequired bytheMHCSScorrespondtoasustainedwind speedofaround70milesperhour(mph)in anExposureCarea.Thisisapproximately equivalentto85mphpeakgustwinds.

“New” Manufactured Homes

HurricaneAndrewdestroyednumerousmanufactured homesin1992.Inresponsetothisdamage,the MHCSSstandardswerestrengthenedonJuly13, 1994.Thestrengthenedstandardsapplytohomes placedinhigherwindspeedareas.These1994 revisions,whichremainineffecttoday,established threetypesofhomes:HUDZoneI,HUDZoneII,and HUDZoneIIIhomes.

HUDZoneIhomesarethosehomesdesignedto theoriginal1976standards.

HUDZoneIIhomesaredesignedtoresist sustainedwindspeedsof100mph(equivalentto approximately120mphpeakgustwinds).

HUDZoneIIIhomesaredesignedtoresista sustainedwindspeedof110mph(equivalentto approximately130mphpeakgustwinds).

NOTE:“Sustained”windspeedsareapproximately fastestmilewindspeeds;“gust”windspeedsare approximately3-secondgustswindspeeds.

How Older Manufactured Homes are Vulnerable to High-Wind Events High-windeventssuchastornadoesandhurricanes candamagenearlyallbuildingsnotspecifically designedtoresistthestrongforcesgeneratedby theseevents.New“engineeredbuildings,”those designedbyprofessionalstomeetthelatestbuilding codesandstandards,havegenerallyperformed wellinhigh-windeventswhileolderbuildingsand non-engineeredbuildingsoftenhavenot.Pre-code manufacturedhomes,particularlythosethathavenot beenwellmaintainedandthosethathavehadnonengineeredadditionsormodificationsmadetothem, haveoftenperformedpoorly.

Damagecanbegroupedintotwocategories:direct damagetothehomeitselfanddamagethatresults fromfailuresinthehome’sanchoragesystem.

This home, constructed before 1976, was destroyed in the February 2007 tornadoes.

This home, constructed between 1976 and 1994, was severely damaged by one of the February 2007 tornadoes.

The roof of this older manufactured home was blown off by high winds.

Page 2 of 7 Understanding and Improving Performance of Older Manufactured Homes During High-Wind Events HSFEHQ-07-J-0007/April 2007

The entire roof structure of this older manufactured home was Portions of the roof and wall sheathing of this older lost and wall panels were lifted from the home. manufactured home were lost. Flying debris broke unprotected

glass in the doors and windows.

This older manufactured home once had an attached screened-in porch. The porch roof blew off and lifted portions of the home’s roof. Fortunately, the high winds lasted only seconds and the rest of the roof was not severely damaged. Had the storm lasted longer, the entire roof would have likely been lost.

Loss of roofing likely originated where the roof of the addition was fastened to the home’s roof.

Direct Damage

Directdamageoftenincludesblown-offroofpanels,lossofroofframing,lossofwallpanelsandframing,and breakageofunprotectedwindows.Windowdamageoccursasaresultofhighwindpressuresorfromthe impactofflyingdebrisgeneratedbyhighwinds.

Comparedtonewmanufacturedhomes,theroofsandwallsofmanyoldermanufacturedhomesarepoorly fastened,particularlythoseconstructedbefore1976.Damagefromhigh-windeventsisquitecommon.Once wallsandroofsaredamaged,rainwatercanfreelyenterthehomeandsaturateitsinterior.Waterdamage oftenresultsinatotallossofthehomeanditscontents.

Thepotentialfordamagetomanufacturedhomesisincreasedsignificantlywhenadditionslikecarports, awnings,orporchesarefastenedtothehome.Theseadditionsconcentratewindforceswheretheyare fastenedtothehome.Theincreasedforcescanoverloadconnectionsusedtoholdthehometogether andcanresultinafailureofthemembersorconnectionsinthehome.Mosthomemanufacturersprohibit attachmentstotheirhomesunlessspecialprovisionstosupportattachmentswereincorporatedintothe homewhenitwasmanufactured.Theattachmentsthemselves,unlessengineered,alsoviolatelocalcode requirementsinmanyjurisdictions.

Reroofingisanothertypeof“addition”thatinvolvesinstallinganewroofcoveringoranewroofstructureover anexistingroof.Dependingonthemethodusedtoattachthenewroof,windloadscanbeconcentratedinto


These photos show the failure of an attached porch roof. Uplift forces acting on the roof of the attached porch caused it to lift. When the roof lifted, it destroyed the porch roof and damaged the roof over the original home. Where open areas exist, as in

These photos shows the failure of a “reroof.” Uplift forces at the edges of the roof caused portions of the added roof to lift and peel off the manufactured home.

the porch shown, the addition must resist uplift forces that act on the top and underside of the roof.

onlyafewmembersorconnections.Theconcentrationofwindloadscanoverloadmembersandconnections andcanresultinstructuralfailures.Also,manyreroofscreateroofoverhangsthat,whiledesirablefroma homemaintenancestandpoint,increaseloadsonthehomeanditsfoundationandmakethehomemore vulnerabletowinddamage.

Anchorage Failure

Anchoragefailuresinvolvethehomebeinglifted,slid, orrolledoffitsfoundation.Ananchoragefailurecan destroyahomeevenwhenthereisnodirectwind damagetothehomeitself.

Anchoragefailuresaremuchmorecommoninolder homesthaninnewerhomes.Olderhomesgenerally weighlessthannewermanufacturedhomesand arethusmorevulnerabletodisplacementfromwind forces.Historically,itappearsthatminimalattention waspaidtotheanchorageofthesehomescompared totheobservedanchoragesinnewerhomes.

Anchoragefailurestypicallyresultfrom:

Toofewanchorsusedtosecurethehome

Improperanchorsselectedforthesoilspresent onsite

This manufactured home rolled off its foundation after anchors used to secure it pulled out of the ground. Only six anchors (three per side) secured the 30-foot-long section of home. Twelve anchors would have been appropriate. The home lifted off its foundation and rolled approximately 70 feet before coming to a rest on its roof.

Corrodedanchorsoranchorstraps

Page � of 7 Understanding and Improving Performance of Older Manufactured Homes During High-Wind Events HSFEHQ-07-J-0007/April 2007

The ground anchor above pulled out of the ground 8 inches. This ground anchor failed just below the anchor head where Either improper anchors were selected or too few were installed. corrosion had weakened the anchor shaft. Like many older-style The anchor spacing at this home was approximately 12 feet. anchors and straps, the anchors and straps were not galvanized

and were susceptible to corrosion.

This 4-foot-long ground anchor with a 6-inch diameter helix pulled out of the soil. Soils in the area consisted of loose sands. Longer anchors with larger diameter helices would have been a better choice for this soil type. The anchor spacing at this home was approximately 10 feet.

ThefollowingexamplesofanchoragefailureswereobservedinoldermanufacturedhomesaftertheFebruary 2007Floridatornadoes.

Recommendations Home Strengthening

Unfortunately,relativelyfewinexpensivemeasuresexistthatcansignificantlyincreasethestrengthofanolder manufacturedhome.Mostfastenersthatholdahometogetherareconcealedandthehomewouldneedto bepartiallydisassembledtogainaccesstoimproveconnections.Also,particularlyinthecaseoftheroof, addingfastenersusuallyinvolvespenetratingexteriorsurfacesofthehomeandthesepenetrationsincrease thepotentialforleakage.

Toincreasethewindresistanceoftheroof,additionalfastenerscanbeinstalledtobetterfastenthemetal roofpanelstotheroofframing,followedbytheinstallationofasingle-plyroofmembrane.Aspartofthe improvements,portionsofthemetalroofpanelscanberemovedtoaccessareaswheretheroofframing connectstothewallframing.Thiswillenableroof/wallconnectionstobestrengthened.

Ifanewroofstructureovertheexistingroofisdesired,thenewstructureshouldbedesignedtoresist componentsandcladdingloadsforthebasicwindspeedidentifiedinthe2006International Residential Code,the2006editionofNationalFireProtectionAssociation(NFPA)5000Building Construction and Safety


Code,orAmericanSocietyofCivilEngineers(ASCE)7-05Minimum Design Loads for Buildings and Other Structuresforthesiteonwhichthehomeislocated.

Attachments and Attached Structures

Homeownersareadvisedthat,priorto1994,mosthomeswerenotdesignedorapprovedbythemanufacturer tohaveattachmentsconnectedtothem.Attachedstructuresshouldnotbeaddedtohomesnotdesignedto supportthem.Allattachmentsorstructuresattachedtoexistingoldermanufacturedhomesshouldberemoved orreconfiguredsotheyaresupportedindependentlyofthehome.Forbestperformance,noconnections, otherthanflashingrequiredforweather-tightness,shouldremainbetweenthemanufacturedhomeandthe addition.Regardlessofwhethertheaddedstructureisattachedtothehomeorisfree-standingnexttoit,all addedstructuresshouldbeconstructedtomeetlocalcoderequirementsusingthesamestandardsasthose forresidentialsite-builtconstruction.Thedesignofadditionsshouldnotusereducedwindcriteriathatare occasionallyconsideredforancillarystructureslikeagriculturalbuildingsandminorstoragefacilities.Whereno codeislocallyadopted,the2006International Residential Code,the2006International Building Codeorthe 2006editionofNFPA5000 Building Construction and Safety Codeshouldbefollowed.

Anchorages and Strapping

Anchorsandstrapsshouldbeinspectedregularlyandallcorrodedstrapsoranchorsshouldberemovedand replacedandallloosestrapsshouldbetightened.Specifictensioninglimitsareusuallynotspecifiedinground anchorormanufacturedhomeinstallationinstructions.However,thestrapsshouldbetightenedsufficientlyto removeallslackandtoallowthestraptomoveonly¼inchorsounderfirmhandpressure.Ininteriorareas (morethan3,000feetfromthecoast)anchorsandstrapsshouldbeinspectedevery5years.Forhomes situatedwithin3,000feetofthecoast,anchorsandstrapsshouldbeinspectedevery2years.Whennew anchorsandstrapsareinstalled,onlygalvanizedmaterials(withaminimumcoatingof0.6ouncepersquare foot)shouldbeused.Anchorheadsshouldremainapproximately1inchaboveadjacentgradetohelpprevent corrosionresultingfromwateraccumulatingneartheanchorheadandstrap.

High-windeventscancausehomessecuredwithgroundanchorstoshiftacrosstheirpiers.Thisshift increasesloadsonportionsofthefootingsbelowthepiers,whichincreasesthepotentialforfootingdamage. Shiftingalsomakesthehomemorevulnerabletoanchoragefailuresduringsubsequenthigh-windevents. Whenthecenterlineofthehome’sframeisnotlocatedwithin2½inchesofthecenterofitspiers,thehome shouldbeliftedandre-settoproperlycenterthehome’ssteelframes.

Whenahomeisexposedtohighwinds,itcanmove(asdescribedabove)andcauseanchorsandstrapsto becomeloose.Loosestrapsrenderanchorsineffectiveatresistingwindsfromsubsequentevents.Anchor strapscanloosenevenwithoutahomebeingexposedtohighwinds,particularlyifsoilsarerelativelysoftor ifanchorswereinadequatelypre-tensionedaftertheirinstallation.Forthesereasons,manufacturedhomes securedwithgroundanchorsshouldhavetheiranchorscheckedperiodicallyandre-tensionedwhenstrapsare foundloose.Asdescribedabove,loosestrapsshouldbetightenedtoremoveallslackandtoallowthestrap tomoveonly¼inchorsounderfirmhandpressure.

Homesshouldbeanchoredinboththelateralandlongitudinaldirection.Lateralanchoragerequirements dependonthedesignwindspeedfortheareaandonthelengthandwidthofthehome.Thegreaterthedesign windspeed,theclosertherequiredanchorspacing.Also,narrowsingle-unithomes,whicharemoreproneto overturning,requirecloseranchorspacingthanwiderdouble-unithomesandlongerhomesrequiremorelateral anchorsthanshorterhomes.Thetypeofpadsusedunderthemasonrypiersthatsupportthehomeshouldalso beconsidered.CloseranchorspacingissuggestedwhenABS(AcrylonitrileButadieneStyrene)padsareused. ABSpadsarearelativelynewstyleofpadthatisusedinlieuofheavierconcretepads.Theyarelightweightand typicallymanufacturedfromrecycledplastics.Closeranchorspacingwilllimithomemovementandwillhelp preventfracturingoftheABSpads.Lateralgroundanchorsshouldalsobeplacedwithin2feetoftheendsof thehome.Usethetableonthefollowingpagetoidentifymaximumintervalspacingandcalculatethenumber ofanchorsneededforlateralanchorage.Forexample,ifadouble-widehomeissitedina110mphwindzone andplacedonconcretepads,itshouldhavegroundanchorsspacedatmaximumintervalsof6feet,8inches. Therefore,a64-foot-longdouble-widehomewouldrequire20lateralanchors(10perside)anda72-foot-long double-widehomewouldrequire24anchors.Forlongitudinalanchorage,4groundanchorspersectionendare recommended.Atotalof8longitudinalgroundanchorsshouldbeinstalledforsingle-widehomesand16should beinstalledfordouble-widehomes.

Page � of 7 Understanding and Improving Performance of Older Manufactured Homes During High-Wind Events HSFEHQ-07-J-0007/April 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. ForHUDZoneIstylehomes,eachlateralgroundanchorshouldbestrappedtothenearestandfurthestI-beam.ForHUD ZoneIIandZoneIIIhomes,eachlateralgroundanchorshouldbestrappedtothefurthestI-beamandthecorresponding walltie.

(3)Whenthemanufacturer’sinstallationinstructionsorlocalcodesspecifygroundanchorspacingdifferentthanthatlisted above,anchorsshouldbeinstalledattheclosestanchorspacingspecifiedforimprovedresistancetohurricanesand tornadoes.

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

Whennoprovisionsexisttotieanoldermanufacturedhome’swallstotheanchoringsystem,over-the-roofties helppreventdirectdamagetothehome.However,theeffectiveinstallationofover-the-rooftiesischallenging. Over-the-rooftiesneedtobeplaceddirectlyoverroofframingmemberssotheydonotdeformorpuncture theroof.Theyalsoneedtobefastenedinplacetoensuretheydonotmoveofftheroofframingmembers. Fasteningover-the-roofstrapsrequirespenetratingtheroof.Thiswillincreasethepotentialforroofleaks.

TheFloridaDepartmentofHighwaySafetyrequirementsincludeprovisionsforover-the-roofties.Theirstandards placeover-the-rooftiesatroughly20-footintervals.Investigationsfollowingrecenttornadoesrevealednumerous homesweredamagedordestroyedthathadfactoryorfield-installedrooftiesinstalledinthe18-footto20-foot range.Thissuggeststhatcloserover-the-rooftiespacingisprudent.Whengroundanchorsareinstalledatthe spacingrecommendedabove,placinganover-the-rooftieateveryothergroundanchorisappropriate.When groundanchorsarespacedat8-footintervals,over-the-rooftiesshouldbelocatedateachanchor.

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

Understanding and Improving Performance of Older Manufactured Homes During High-Wind Events HSFEHQ-07-J-0007/April 2007 Page 7 of 7

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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.


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

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.

Page 2 of 8 Understanding and Improving Performance of New Manufactured Homes During High-Wind Events HSFEHQ-07-J-0007/April 2007

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.


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.

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

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.


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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).

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

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

Understanding and Improving Performance of New Manufactured Homes During High-Wind Events HSFEHQ-07-J-0007/April 2007 Page 7 of 8

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

tornado risks and hazards in the southeastern united states

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