siding installation in high-wind regions - fema.gov · 2013-07-26 · siding installation in...

Siding Installation inHigh-Wind RegionsHURRICANE IKE RECOVERY ADVISORY

of 7Siding Installation in High-Wind Regions January 2009

Purpose: To provide basic design and installation tips for various types of siding that will enhance wind resistance in high-wind regions (i.e., greater than 90-mph gust design wind speed).

Key Issues•Sidingisfrequentlyblownoffwallsofresidentialand

non-residential buildings during hurricanes. Also, wind-drivenrainisfrequentlyblownintowallcavities(evenwhen the siding itself is not blown off). Guidance for achieving successful wind performance is presented below.

•Toavoidwind-drivenrainpenetrationintowallcavities,aneffective moisture barrier (housewrap or building paper) is needed. For further information on moisture barriers, seeTechnicalFactSheetNo.9inFEMA499,Home Builder’s Guide to Coastal Construction, Technical Fact SheetSeries(availableonlineat:http://www.fema.gov/library/viewRecord.do?id=1570). For further information onhousewrap,seeTechnicalFactSheetNo.23.

•Alwaysfollowmanufacturer’sinstallationinstructionsandlocalbuildingcoderequirements.

•Useproductsthataresuitableforacoastalenvironment.Manymanufacturersdonotratetheirproductsinawaythat makes it easy to determine whether the product willbeadequateforthecoastalenvironment.Useonlysiding products where the supplier can provide specific information on product performance in coastal or high-wind environments.

•Forbuildingslocatedwithin3,000'oftheoceanline,stainless steel fasteners are recommended.

•Avoidusingdissimilarmetalstogether.

•Theinstallationdetailsforstartingthefirst(lowest)courseoflapsidingcanbecritical.Lossofsidingoftenbeginsatthelowestcourseandproceedsupthewall(Figures4and12).Thisisparticularlyimportantforelevated buildings, where the wind blows under the building as well as against the sides.

•Whenapplyingnewsidingoverexistingsiding,useshimsorinstallasolidbackingtocreateauniform,flatsurface on which to apply the siding, and avoid creating gaps or projections that could catch the wind.

•Coastalbuildingsrequiremoremaintenancethaninlandbuildings.Thismaintenancerequirementneedstobe considered in both the selection and installation of siding.

Vinyl SidingVinyl siding can be used successfully in a coastal environment if properly designed and installed.

•Windloadresistance:

Moisture barrier (also known as a water-resistivebarrier):Inthecontextofresidential walls, the moisture barrier is either housewrap or building paper (felt). The moisture barrier occurs between the wallsheathingandthesiding.Itisadual-purpose layer that sheds water that gets throughthesidingandlimitsairflowthroughthewall.Whenproperlysealed,housewrapis considered an air barrier. Although building paper provides some resistance to airflow,itisnotconsideredanairbarrier.Moisturebarriersshedwater,buttheyallowwater vapor to pass through them.

For further guidance on principles, materials, and procedures for the design and construction of walls to make them resistant to water intrusion, see American SocietyforTestingandMaterials(ASTM)E2266,Standard Guide for Design and Construction of Low-Rise Frame Building Wall Systems to Resist Water Intrusion.

http://www.fema.gov


•VinylsidingisrequiredbytheInternationalBuildingCode®(IBC®)andtheInternationalResidentialCode®(IRC®)tocomplywithASTMD3679,Standard Specification for Rigid Poly(Vinyl Chloride) (PVC) Siding,whichrequiresthesidingtowithstandwindpressuresequivalentto110mphonabuildingupto30'inheightinExposureB.Mostvinyl siding has also been tested for higher wind pressures, and can be used in locations with a higherbasicwindspeed,greaterbuildingheight,moreopenexposure,orsomecombinationofthose.The design wind pressure or wind speed for which these products are rated is available from product literature,installationinstructions,orlistingsofagenciessuchastheInternationalCodeCouncil®(ICC®)EvaluationService.

•Fordesignwindspeedsgreaterthan110mph,orbuildingheightsgreaterthan30',orExposureC,chooseamodelofsidingratedforthoseconditionsorhigher.Themanufacturer’sproductliteratureorinstallation instructions should specify the fastener type, size and spacing, and any other installation details needed to achieve this rating.

•Productsthathavebeenratedforhighwindstypically have an enhanced nailing hem and are sometimesmadefromthickervinyl(Figure1).Thick, rigid panels provide greater wind resistance, withstanddents,andlieflatterandstraighteragainst the wall. Optimum panel thickness should be0.040to0.048",dependingonstyleanddesign. Thinner gauge vinyl works well for stable climates; thicker gauge vinyl is recommended for areas with high winds and high temperature changes.

•Positionnailsinthecenterofthenailingslot(Figure2).

•Toallowforthermalmovementofthesiding,donotdrive the head of the nail tight against the nail hem (unless the hem has been specifically designed forthis).Allowapproximately1/32"(whichisaboutthethickness of a dime) clearance between the fastener head andthesidingpanel(Figure3).

•Drivenailsstraightandleveltopreventdistortion and buckling in the panel.

•Donotcaulkthepanelswheretheymeetthereceiver of inside corners, outside corners, or J-trim.Donotcaulktheoverlapjoints.

•Donotface-nailorstaplethroughthesiding.

•Usealuminum,galvanizedsteel,orothercorrosion-resistant nails when installing vinyl siding.Aluminumtrimpiecesrequirealuminumorstainlesssteelfasteners.

•Nailheadsshouldbe5/16"minimumindiameter.Shankshouldbe1/8"indiameter.

•Usethemanufacturer-specifiedstarterstriptolockinthefirstcourse;donotsubstituteotheraccessoriessuchasaJ-channelorutilitytrim(Figure4)unlessspecifiedbythemanufacturer.Ifthemanufacturerspecifiesaparticularstripforhigh-windapplications,useit.Makesurethatthestarterstripisdesignedto positively lock the panel, rather than just hooking over a bulge in the strip; field test the interlock before proceeding with the installation.

Figure 1. Features of typical high-wind siding and standard siding.

Definition of Wind Exposure ZonesExposure B: Urban,suburban,woodedareas.

Exposure C:Openterrain,flatopencountry,grasslands, all water surfaces in hurricane-prone regions.

High-wind siding Standard siding

Figure 2. Proper and improper fastener locations.

Figure 3. Allow 1/32” clearance between the fastener head and the siding panel.


•Makesurethateverycourseofsidingispositivelylockedintothepreviouscourse(Figure5).Pushthe panel up into the lock from the bottom before nailingratherthanpullingfromthetop.Donotattempt to align siding courses with adjacent walls by installing some courses loosely.

•Makesurethatadjacentpanelsoverlapproperly,about half the length of the notch at the end of the panel,orapproximately1".Makesuretheoverlapis not cupped or gapped, which is caused by pulling up or pushing down on the siding while nailing. Reinstallanypanelsthathavethisproblem.

•Useutilitytrimunderwindowsoranywherethetopnail hem needs to be cut from siding to fit around anobstacle.Besuretopunchsnap-locksintothesidingtolockintotheutilitytrim.Donotoverlapsidingpanelsdirectlybeneathawindow(Figure6).

•Atgableendwalls,itisrecommendedthatvinylsidingbeinstalledover wood sheathing rather than over plastic foam sheathing, as wasdoneatthehouseshowninFigure7.

•Installvinylsidinginaccordancewithmanufacturer’sinstallationinstructionsandlocalbuildingcoderequirements.

•ItisrecommendedthatvinylsidinginstallersbecertifiedundertheVSICertifiedInstallerProgramsponsoredbytheVinylSidingInstitute.Formoreinformation,gotohttp://www.vinylsiding.org/aboutsiding/installation/certinstaller.

Figure 4. Utility trim was substituted for the starter strip and the bottom lock was cut off the siding. Siding was able to pull loose under wind pressure.

Figure 7. The vinyl siding at this gable was installed over plastic foam insulation. Without wood sheathing, the wind pressures on the vinyl are increased. Also, if the siding blows away, the foam insulation is very vulnerable to blow-off. With loss of the foam insulation, wind-driven rain can freely enter the attic, saturate the ceiling insulation, and cause collapse of the ceiling.

Figure 5. The siding panel was not properly locked into the panel below.

Figure 6. Proper detailing around windows and other obstacles is important. Use utility trim, punch snap-locks into siding, and don’t overlap directly beneath a window.


Wood Siding•Usedecay-resistantwoodsuchasredwood,cedar,orcypress.SeetheSustainableDesignsectionregarding

certified wood.

•Toimprovelongevityofpaint,back-primewoodsidingbeforeinstallation.

•Carefullyfollowmanufacturer’sdetailinginstructionstopreventexcessivewaterintrusionbehindthesiding.

•Forattachmentrecommendations,seeNatural Wood Siding: Selection, Installation and Finishing, published bytheWesternWoodProductsAssociation(http://www.wwpa.org).

This publication recommends an air gap between the moisture barrier and the backside of the siding to promotedrainageandventilation.Suchawallconfigurationisreferredtoasarainscreenwall.Seethetextboxonpage5.

•FollowtheinstallationdetailsshowninFigure8.(Note:Althoughthesedetailsdonotshowarainscreen,inclusion of vertical furring strips to create a rain screen is recommended.)

Figure 8. Wood siding installation details.

Seal joints

Corner boards

Woodsheathing

Housewrap orbuilding paper

Interiorwall finish

Vapor retarder(if needed)

Insulation

Wood sheathing

Bevel siding

Self-adheringmodified bitumenflashing


Tongue and groove horizontalsiding up to 6" wide

Tongue and groove horizontalsiding up to 6" wide

Seal joints

Cornerboards

Self-adhering modifiedbitumen flashing

Bevelsiding

Woodsheathing

Trim

Stud

Housewrap or building paper

Wood sheathing

Nails must penetrate solidwood 1-1/2" minimum

Extra nail

Wood stud

Wood sheathing

Housewrapor buildingpaper

Tongue andgroovehorizontal siding

Lap at 45°


Fiber Cement SidingInstallationproceduresaresimilartothoseforwoodsiding,butrequirespecializedcuttingbladesandsafetyprecautionsbecauseofthedustproducedduringcuttingwithpowertools.Manufacturer’sinstallationrecommendations should be strictly adhered to, and particular attention paid to the painting and finishing recommendationsforahigh-qualityinstallation.

•Alwayssealfield-cutendsaccordingtothemanufacturer’sinstructions.Properlygaptheintersectionbetween siding edges and other building components and fill the gap with sealant.

•Alwaysconsultandfollowthemanufacturer’sinstallationrequirementsfortheneededwindspeedratingordesignpressure(refertothemanufacturer’sbuildingcodecomplianceevaluationreport).Observethemanufacturer’sfastenerspecifications,includingfastenertypeandsize,spacing,andpenetrationrequirements.Donotoverdriveorunderdrive.

•Atgableendwalls,itisrecommendedthatfibercementsidingbeinstalledoverwoodsheathingratherthanover plastic foam sheathing.

•Keepblindnailsbetween¾and1"fromthetopedgeofthepanel(Figure10).Besuretodrivenailsatleast3/8"frombuttends,orusemanufacturer-specifiedjoiners.

•Facenailing(Figure11)insteadofblindnailingisrecommendedwherethebasic(design)windspeedis100milesperhourorgreater.Ifthelocalbuildingcodeormanufacturerspecifiesfacenailingatalowerwindspeed, install accordingly.

•Donotleavetheundersideofthefirstcourseexposedorextendingbeyondtheunderlyingmaterial(Figure12).Considertheuseofatrimboardtocloseofftheundersideofthefirstcourse.

Pressure-equalized rain screen wall systemInareasthatexperiencefrequentwind-drivenrainandareas susceptible to high winds, it is recommended that a rain screen design be considered when specifying wood or fiber cement siding. (Typical vinyl siding products inherently provide air cavities behind the siding that facilitate drainage. Therefore, incorporation of vertical furring strips is normally not applicable to this type of wall covering.) A rain screen design is accomplished by installing suitable vertical furring strips between the moisture barrier and siding material (see Figure 9). The cavity facilitates drainage of water from the space between the moisture barrier and backside of the siding and it facilitates drying of the siding and moisture barrier.

Furring strip attachment: For1"x2" furring strips, tack strips inplaceandusesidingnailsthatare¾" longer than would berequirediftherewerenostrips(therebymaintainingtheminimallyrequiredsidingnailpenetrationintothestuds).For thicker furring strips, an engineered attachment is recommended.

At the bottom of the wall, the cavity should be open to allow water drainage. However, the opening should be screened to avoid insect entry.

Atthewall/soffitjuncture,thetopofthecavitycanopenintotheatticspacetoprovideinletairventilation,therebyeliminatingsoffitventsandtheirsusceptibilitytowind-drivenrainentry.Iftherainscreen cavity vent path is used in lieu of soffit vents, the depth of the cavity needs to be engineered to ensurethatitprovidessufficientairflowtoventilatetheattic.

Pressure-treated ordecay-resistant furring strips

Bevel siding


Wood sheathing

Stud

Figure 9. Pressure-equalized rain screen system.


Sustainable DesignMaterial selection for sustainable sources and durability

Forwoodproducts,selectaForestStewardshipCouncil(FSC)certifiedproduct.TheFSCseekstoensurethatwood is harvested in a more responsible fashion, including protecting forest ecosystems, and avoids theuseofchemicalsandgeneticengineering.Whileredwood, cedar, and cypress are decay-resistant and recommended for durability, they are generally cut from old growth timber. You can determine if the manufacturer isFSCcertifiedbygoingtohttp://www.fsc-info.org.

For other siding products, consider long-term life spans for coastal environments, recycled content, and post-consumer use.

The following publications discuss sustainable aspects of vinyl siding:

A Dozen Things You Might Not Know That Make Vinyl Siding Green (available online at http://www.vinylsiding.org/aboutsiding/greenpaper/080919_VSI_Green_Paper_for_web.pdf).

Siding with the Environment (available online at http://www.vinylsiding.org/publications/final_Enviro_single_pg.pdf).

Energy Conservation and Air Barriers: Uncontrolledairleakagethroughthebuildingenvelopeisoftenoverlooked.TheU.S.DepartmentofEnergyestimatesthat40percentofthecostofheatingorcoolingtheaverageAmericanhomeislosttouncontrolledairleakage.Inwarmerclimates,itisalowerpercentageofloss.Anairbarriersystemcanreducetheheating,ventilation,andcooling(HVAC)systemsize,resultinginreduced energy use and demand.

Uncontrolledairleakagecanalsocontributetoprematuredeteriorationofbuildingmaterials,moldandmoistureproblems,poorindoorairquality,andcompromisedoccupantcomfort.Whenuncontrolledairflowsthroughthebuildingenvelope,watervapormoveswithit.Controllingthemovementofmoisturebyairinfiltrationrequirescontrollingtheairpathwaysand/orthedrivingforce.

Toeffectivelycontrolairleakagethroughthebuildingenvelope,aneffectiveairbarrierisrequired.Tobeeffective, it needs to be continuous; therefore, air barrier joints need to be sealed and the barrier needs to besealedatpenetrationsthroughit.TheAirBarrierAssociationofAmericarecommendsthatmaterialsused

Face Nail

Stud

Water-resistivebarrier

Face nail

24"

o.c. maximum

Siding

¾"-1"

Face Nail

Face nail

Siding

¾"-1"

A graphic change needs to be made at the left stud of fig 10. Either do a cut-away like you do at fig 9 or at the vertical line that indicates a joint in the lower siding, dash the portion of the line that extends above the next course of siding. For consistence, of these 2 options, I prefer the first one.

I think it would be clearer if the vertical line representing the joint between the two lower boards was not visible at all under the upper boards. The line repre-senting the top edge of the lower boards is not shown under the upper board. I think if the vertical joint just ends at the bottom edge of the upper boards, it will be clear enough that the two nails are located on ether side of the joint, and be a less cluttered view.


Stud

Wood sheathing

Figure 11. Face nailing.

Figure 12. Blind nailed siding installed with exposed gap at bottom (red circle) is vulnerable to failure.

Stud

Blind nail

Siding

Blind Nail

¾"-1"

Stud

Blind nail

Siding

Blind Nail

¾"-1"

A graphic change needs to be made at the left stud of fig 10. Either do a cut-away like you do at fig 9 or at the vertical line that indicates a joint in the lower siding, dash the portion of the line that extends above the next course of siding. For consistence, of these 2 options, I prefer the first one.



Wood sheathing

Figure 10. Blind nailing.


asacomponentofabuildingenvelopeairbarrierbetestedtohaveanairinfiltrationrateoflessthan0.004cfm/squarefoot,assembliesofmaterialsthatformtheairbarrierbetestedtohaveanairinfiltrationrateoflessthan0.04cubicfeetperminute(cfm)/squarefoot,andthewholebuildingexteriorenclosurehaveanairinfiltrationrateoflessthan0.4cfm/squarefoot.

Air barrier systems installed behind siding:

Housewrap is the most common air barrier material for residential walls. To be effective, it is critical that the joints between sheets of housewrap be sealed as recommended by the manufacturer, and penetrations (other than fasteners) should also be sealed. At transitions between the housewrap and door and window frame, use of self-adheringmodifiedbitumenflashingtapeisrecommended.

An air barrier should be installed over a rigid material, or itwillnotfunctionproperly.Italsoneedstoberestrainedfrom pulling off of the wall under negative wind pressures. For walls, wood sheathing serves as a suitable substrate, and the siding (or furring strips in a rain screen wall system) provide sufficient restraint for the air barrier.

At the base of the wall, the wall air barrier should be sealedtothefoundationwall.Ifthehouseiselevatedonpiles, the wall barrier should be sealed to an air barrier installedattheplaneofthefloor.

Ifthebuildinghasaventilatedattic,atthetopofthewall,the wall air barrier should be sealed to an air barrier that is installed at the plane of the ceiling.

Ifthebuildinghasanunventilatedatticornoattic,atthetop of the wall, the wall air barrier should be sealed to an air barrier that is installed at the plane of the roof (the roof air barrier may be the roof membrane itself, or a separate air barrier element).

Siding maintenance:

For all siding products, it is very important to periodically inspect and maintain the product especially in a coastal environment. This includes recoating on a scheduled maintenance plan that is necessary according to the manufacturer’sinstructionsandaperiodiccheckofthesealanttoensureitsdurability.Checkthesealantforitsproperresiliencyandthatitisstillinplace.Sealantshouldbe replaced before it reaches the end of its service life.

Air barrier: A component installed to provide a continuous barrier to the movement of air through the building envelope. Housewrap is a common air barrier material for residential walls.Althoughveryresistanttoairflow,housewrap is very vapor permeable and therefore is not suitable for use as a vapor retarder.

Vapor retarder: A component installed to resist diffusion of water vapor and provide a continuous barrier to movement of air throughthebuildingenvelope.Polyethyleneis a common vapor retarder material for residential walls. To determine whether or not a vapor retarder is needed, refer totheMoistureControlsectionoftheNRCA Roofing and Waterproofing Manual, publishedbytheNationalRoofingContractorsAssociation(NRCA)(http://www.nrca.net).

ASTME1677,Standard Specification for an Air Retarder (AR) Material or System for Low-Rise Framed Building Walls:This specification covers the minimum performance and acceptance criteria for an air barrier material or system for framed walls of low-rise buildings with the service life of the building wall in mind. The provisions contained in this specification are intended to allow the user to design the wall performance criteria and increase air barrier specifications to accommodate a particular climate location, function, or design of the intended building.

siding installation in high-wind regions - fema.gov · 2013-07-26 · siding installation in...

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