What size OSB should you use for roof decking?
Short answer. Most residential roofs use 4 by 8 foot sheets of 7/16 inch OSB over rafters or trusses spaced 24 inches apart, with metal H-clips at unsupported panel edges. Step up to 1/2 or 5/8 inch when the framing is irregular or wider apart, when you want a stiffer and flatter roof, or when local requirements call for it.
Reading the panel stamp
Every structural OSB panel carries a grade stamp with a span rating such as 24/16. The first number is the maximum rafter or truss spacing in inches for roof use; the second is for floors. A 7/16 inch panel is commonly rated 24/16, so it can span 24 inch framing on a roof when its edges are supported. Also check the bond classification, usually Exposure 1, which means the panel can handle weather during construction.
Common choices
- 7/16 inch: the standard on most new homes with 24 inch framing.
- 15/32 or 1/2 inch: a little stiffer, often used where framing is irregular or for a better walking surface.
- 19/32 or 5/8 inch: much stiffer and holds nails better, worth considering on wider spans or for a full redeck.
Installation details that matter as much as size
- Long side of the panel runs across the rafters, with end joints staggered.
- A 1/8 inch gap at edges and ends to allow for swelling.
- H-clips at unsupported edges between framing members.
- Nailing to the framing per code, which tightens up in higher wind areas.
- Textured side up, so the crew has grip.
Matching during repairs
When only a few sheets are replaced during a reroof, match the existing thickness so the new shingles lie flat. See OSB vs plywood roof decking and roof anatomy explained.