What is roof decking made of?
Plywood
Thin sheets of veneer are peeled from logs, glued with alternating grain direction and pressed. The cross grain makes it strong and stable. It handles brief wetting well and dries out without much swelling, and many roofers prefer it for that reason.
OSB (oriented strand board)
Wood strands are coated with waterproof resin and wax, laid in cross-oriented layers and pressed into panels. OSB is consistent, has no voids and costs less than plywood, which is why it dominates new construction. Its edges swell if they stay wet, and it dries slowly.
Solid boards
Many older homes have 1x6 or 1x8 boards nailed across the rafters. Some have gaps between boards; if the gaps are too wide for shingle nails to land solidly, the roof needs an overlay of new panels before shingling.
Specialty panels
- Radiant barrier sheathing: OSB or plywood with foil on the attic side.
- Integrated barrier panels: OSB with a factory water-resistant overlay and taped seams.
- Fire retardant treated plywood: used in some attached homes near the walls between units where code calls for it.
- Tongue and groove planks: thick wood decking that doubles as a finished ceiling.
Commercial roofs
Steel deck, concrete, gypsum and wood fiber decks show up on commercial buildings under insulation and membrane roofing.