Wood Plank - If you have a wood plank roof deck, it is not recommended
that the wood planks exceed eight inches (8") in width due to their
propensity for warping.
Plywood - If you have a plywood roof deck,
make sure that you have at least 15/32" (or ½") plywood thickness if the
rafters are set at sixteen inches (16") on center. If your rafters are
twenty-four inches (24") on center, it is recommended that your plywood is
at least 5/8" inches thick. All plywood should be Exposure 1 Rated plywood
and be rated for structural use by the APA-The
Engineered Wood Association. This is indicated by
a stamp on the plywood that states "32/16" rated. What this means is
that particular board is rated for sub-flooring where the floor joists are
16" on center and for roof decking where the rafter or roof joists are 32"
on center. The APA
recommends a 1/8" gap be left between adjacent panels of plywood/OSB.
Oriented Strand Board (OSB) – If you have an OSB deck, it is
recommended that 15/32" is used for rafters on sixteen inch (16") centers.
Thickness requirements of OSB and plywood is determined by design load
requirements and the distance between the rafters. The
APA recommends a 1/8" gap be left between adjacent panels of plywood/OSB.
OSB ratings are found on a stamp located on one
side of the sheet.
Deck Repair/Replacement (Plywood) - Deck replacement
should be done in full four foot (4') by eight foot (8') sheets at a time
rather than in pieces. This will help prevent sumps and other structural
problems. It is also recommended that "H"-clips be used between all rafters
Both plywood and OSB panels are usually manufactured as performance rated
panels. As such, the thickness of the panel is kind of an independent
variable based on the dependent variables of roof loads, required
deflections and spans. In the marketplace, most manufacturer's panels
that have a 32/16 Span Rating are manufactured as 15/32" thickness.
Full nominal 1/2" thick panels are available and also have a 32/16" Span
Special thanks to:
Senior Engineered Wood Specialist, Field Services Division
APA--The Engineered Wood Association