OSB’s dimensional stability, consistency, sustainability, and wide availability have made it a popular choice for wall sheathing. But even with a high-quality product, smart installation techniques are key to ensuring a successful sheathing job underneath the siding. Here are six strategies to follow.
1. Start by looking for the APA grade stamp. Here’s what to evaluate:
Panel grade: There are three general classes: Sturd-I-Floor, Rated Siding, or Rated Sheathing. Rated Sheathing is an unsanded sheathing for wall, roof, subflooring, and industrial applications. Also available is Structural I Rated Sheathing, for when shear and cross-panel strength properties are of maximum importance.
Span rating: Look for this when span is important. Since stud spacing is dictated by code and you are framing either 16 or 24 on-center spacing, your span will be more than covered by an APA-rated sheathing product.
Thickness: That number is important because it will dictate the size and spacing of your fasteners.
Exposure rating (Bond Classification): Panels are classified as Exterior or Exposure 1, referring to the adhesive bond and therefore, says APA, the structural integrity of the panel. Exterior rated panels are suitable for repeated wetting and redrying or long-term exposure to weather. Exposure 1 panels are for uses not permanently exposed to weather; they have a fully waterproof bond and are designed for applications where construction delays may be expected prior to weathering in the structure with appropriate siding.
2. Proper handling: When OSB arrives on site, keep it dry. Store it on blocks, and put a tarp over the OSB. Place spacer blocks under the tarp to let the air flow across the surfaces of the OSB, and let the edges breath as well. This not only keeps the OSB dry, but it also lets the wood fiber in the OSB stabilize by adjusting to onsite humidity conditions.
3. Panel spacing: All wood products change dimension as the wood responds to humidity and moisture. To accommodate for these changes, leave a gap or space between panels, along every edge, which will allow the sheets of OSB to change dimension without buckling. The recommended space is 1/8 inch.
4. Fastener schedule (i.e., “where the nails should go”): Typically, your structure will be framed with studs that are 16-inches on center. For 16 o.c., the fastener schedule calls for a nail every 6 inches around the edge and every 12 inches in the field of the OSB. That many nails may seem like overkill, but remember that you’re not just nailing to keep the OSB from falling off; you’re nailing to give structural integrity to the structure itself, so it can stand up to such things as earthquakes and strong winds.
5. Fastener type: Per APA recommendations, unless special provisions are required, 6d common nails are suitable for panels with a performance category of 1/2 or less; 8d should be used for thicker panels.
6. Nailing strategies: Always work from one corner. Never pin all four corners and then nail the panel interior. Also, place fasteners at least 3/8 inch in from the edge, to give the nail something to grab onto.