In this Roof Report, we will cover some tips and details for roofers to keep in mind when inspecting the wood sheathing and framing structure of the roof. Always check with your local building code requirements and manufacturer recommendations for minimum sheathing thickness, nailing patterns requirements, and rafter spacing.
Roof sheathing includes plywood, oriented strand board (OSB), and composite panels made up of a combination of wood veneers and regenerated wood layers. The two most commonly used for roof decking are Plywood and OSB panels. Plywood is manufactured by gluing together three or more cross-laminated wood, and OSB is produced from multiple layers of rectangular-shaped wood strands adhered, that are arranged in cross-oriented layers.
Prior leaks can cause water damage to the sheathing. Water damage is bad for any part deck and wood framing system. If the leaks are not fixed immediately, these conditions can lead to severe sheathing and possibly structural damage.
Attic Moisture And Roof Decking
Excess moisture in an attic area can cause the sheathing to become excessively moist. Hot temperatures rising from the attic promote mold and mildew on the roof sheathing causing damage. You should always do an attic inspection to evaluate the roof ventilation and any potential issues that could arise from excess moisture content.
Roof sheathing can become broken from damage from a storm and blowing debris. Special should be taken when walking on the roof where a repair may have been made, and the fractured deck may not have been repaired.
Plywood or OSB panels should be laid with the face grain (coated side on OSB) perpendicular to the rafter boards. The long dimension of the sheet known as the strength axis is aligned across the rafters, and the sheets should be installed over two or more spans.
The sheets should be spaced 1/8-inch apart at the ends and edges to allow for proper expansion and always joined over a support. The joints must also sit along the centerline of the framing with at least 1/2-inch of bearing. Manufacturers sometimes recommend the installation of panel edge clips to provide additional support.
The below chart is for your guidance in fastening Plywood or OSB sheathing panels.
|Typical Fastening Schedule|
|Sheathing Thickness||Type of Fastener||Fastener Spacing on Edges||Fastener Spacing at Rafters|
|3/8-inch to 1/2-inch||8 d common nail (2-1/2 inches)||6 inches apart||12 inches apart|
|19/32-inch to 1 inch||8 d common nail (2-1/2 inches)||6 inches apart||12 inches apart|
For most typical installations, 8 d common or ring shank nails are used to fasten the sheets. The fasteners are spaced on the sheet edges 6 inches apart with a minimum of 3/8-inch of space from the fastener and the sheet edge. A spacing of 12 inches on center is used across the rafters. In areas with the wind speed requirements, nails for attaching the roof sheathing are increased. The fastening schedules for high-wind zone locations have specific fastening requirements depending on location. With all fastening scenarios, the fasteners should be driven flush with the panel surface.
In closing, I want to restate, always check with your local building code requirements and manufacturer recommendations for minimum sheathing thickness, nailing patterns requirements, and rafter spacing.
John Kenney has over 45 years’ experience in the roofing industry. John started his career by working as a roofing apprentice at a family business in the Northeast to operating multiple Top 100 Roofing Contractors. As Chief Operating Officer, John is intimately familiar with all aspects of roofing production, estimating, and operations. During his tenure in the industry, John ran business units associated with delivering great workmanship and unparalleled customer service while ensuring strong net profits for his company prior to joining Cotney Consulting Group. If you would like any further information on this or another subject, you can contact John at firstname.lastname@example.org
Disclaimer: The information contained in this article is for general educational information only. This information does not constitute legal advice, is not intended to constitute legal advice, nor should it be relied upon as legal advice for your specific factual pattern or situation.
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