Continuously sheathing with plywood or oriented strand board (OSB), collectively referred to as wood structural panels (WSPs), make walls stronger and more resilient. But these structural panels also make a solid, consistent nail base for anchoring lightweight siding and trim materials, continuous rigid insulation boards, or battens for rain screen siding.
7 Reasons to Use Plywood or OSB as a Nail Base
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Easily meet code requirements while building for better performance.
Play slideshowBenefits of Nail-Base Sheathing
Attaching siding, trim and other cladding components directly to wall framing is becoming increasingly more difficult due to factors such as more exterior layers (housewrap, rainscreens, continuous insulation, etc.) in high-performance wall systems, cost-saving measures that reduce full-length studs or solid blocking, and advanced framing techniques that increase energy efficiency and may result in fewer studs. As an alternative in these situations, the code allows builders to attach siding directly to nail-base structural sheathing when the correct fastening method is used.
Continuous sheathing—fully sheathing all exterior walls with WSPs, including above and below openings and gable ends—is a practical and effective way to meet the code at an affordable cost. In addition, there are numerous advantages to using continuously sheathed plywood or OSB walls as a nail base for siding and trim.
Along with ensuring that siding ends and trim are fastened to a solid substrate, using WSPs as a nail base avoids searching for hidden wall studs, allows for the use of popular siding products when studs are 24 inches on center, and eliminates the need to install additional wall studs, saving time and material expenses. As penetration into the studs is not required, it brings additional savings by using shorter fasteners. A solid nail base also helps reduce callbacks associated with wind-related siding noise complaints.
Full-scale wind-tunnel tests at the Insurance Institute for Business & Home Safety (IBHS) have confirmed that siding attached directly to continuously sheathed plywood and OSB walls can withstand the same wind and weather conditions as siding attached to framing when the correct number and type of siding fasteners are used.
Fastening Guidelines
Wood structural panel sheathing is typically used with popular lightweight siding products including vinyl, wood, APA-Rated lap and panel siding, wood shingles/shakes, fiber cement and synthetic stucco products.
For these lightweight sidings, there are two ways to determine the right fastener type and fastener schedule for attaching to nail-base sheathing. The easiest is to purchase siding with specific fastener recommendations for direct wood sheathing-only attachment in its code-compliance reports, such as APA Product Reports and ICC-ES reports. For siding that does not have specific recommendations for direct WSP attachments, APA – The Engineered Wood Association offers guidance. APA’s complimentary Nail-Base Sheathing for Siding and Trim Attachment guide provides an easy method for determining the type and spacing of siding fasteners to satisfy building codes.
Attaching siding products with weights exceeding 3 psf requires additional consideration. Find information for attaching heavier (up to 11 psf) siding products, including fastener tables with design values for various types of fasteners, in APA’s free Wood Structural Panels Used as Nailable Sheathing publication.
Using continuously sheathed plywood or OSB walls as a nail base for siding and trim offers builders numerous advantages while cost-effectively meeting code requirements. Find additional information on using nail-base sheathing for siding and trim attachment at apawood.org/nail-base-sheathing.
