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 or joists.
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 Rating.
Special thanks to:
Senior Engineered Wood Specialist, Field Services Division
APA--The Engineered Wood Association