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Performance Solid for Vinyl Siding Over Foam Sheathing
Over the last two code development cycles for the International Residential Code, questions have been raised on the performance of vinyl siding installed over foam sheathing. Observed damage from high winds has led to attempts to ban vinyl siding over foam sheathing and require solid backing such as OSB or fiberboard, even in areas where there is a low risk of tornadoes and hurricanes.
The fact is that vinyl siding installed over foam sheathing and studs has a solid record of excellent performance under the wind conditions and in the urban and suburban environments that are typical for most of the U.S.
The key is the proper selection and installation of the siding and foam sheathing products, which must comply with the applicable ASTM standards and must be installed and fastened in accordance with the manufacturers’ instructions and building code requirements.
In the 2007 Supplement to the 2006 International Residential Code, the required nail size for fastening vinyl siding to studs was increased to a shank diameter of 0.120 inches and a head diameter of 0.313 inches. A sufficient length of fastener is required to accommodate the wall sheathing thickness and to penetrate a minimum of 3/4” into wall studs spaced at 16 inches on center.
Additional information on vinyl siding products and installation guidance can be obtained from the Vinyl Siding Institute (VSI), which qualifies vinyl siding for wind load resistance and other performance criteria under its Vinyl Siding Product Certification Program.
In addition, recent recommendations from VSI and the Foam Sheathing Coalition (FSC) clarify requirements for the installation of vinyl siding on a typical foam sheathed wall assembly.
The recommendations call for a 1-1/4 inch minimum penetration of siding nails into wall studs spaced at 16 inches on center.
Also recommended is a minimum foam sheathing thickness of 1/2” extruded polystyrene or polyisocyanurate, or 1” expanded polystyrene. Also included are special recommendations for gable end wall conditions, where damage from severe winds is more commonly observed, regardless of the sheathing or siding material.
These recommendations are based on research and testing conducted by the NAHB Research Center, and they were submitted for consideration at the upcoming ICC code hearings.
For additional information and guidance on wind-resistant foam sheathing installations with vinyl siding and other siding products, refer to the technical resources available at the FSC’s Web site.
Vinyl Siding in Hurricane-Prone Areas
In hurricane-prone areas along the Atlantic Coast and Gulf Coast, it is critical to select a vinyl siding product with the proper design wind pressure rating. These are also the areas where attention to sheathing specification and fastening, wall bracing and roof uplift load path connections become increasingly important.
With proper specification and installation, foam sheathing and vinyl siding products can provide adequate wind pressure resistance in hurricane-prone regions. However, continuous structural sheathing is often needed and may be added to provide adequate wall bracing. Structural sheathing may also be used to resist wind uplift when it is properly detailed for this application.
With energy code requirements increasing and green building guidelines and standards becoming more prevalent, insulating foam sheathing is critical to building affordable, energy-efficient houses. When properly specified and installed in accordance with building code requirements and manufacturer recommendations, vinyl siding over foam sheathing will continue to provide the excellent performance demanded by builders and home owners.
For more information, e-mail Gary Ehrlich at NAHB, or call him at 800-368-5242 x8545.
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