How Thick Roofing Plywood

Sheathing sizes osb and plywood come in thicknesses ranging from 5 16 to 3 4 inch and the thickness needed for a particular roof depends on several factors including rafter spacing expected load.

How thick roofing plywood. A 3 4 sheet is actually 23 32 thick. That s considered to be the minimum. Typical types of wood used for roof sheathing are oriented strand board known as osb and plywood the most popular being osb. Although specialty plywood can have any number of plies above three most plywood is categorized as 3 ply 5 ply or multi ply.

Plywood is often sold in 1 4 1 2 or 3 4 nominal thicknesses but the actual thickness is often 1 32 thinner. Standard roof sheathing which consists of 4 by 8 sheets of plywood or oriented strand board or osb is 1 2 inch thick and attaches directly to the roof rafters or the roof trusses. That will suffice on a roof with rafters set 16 inches apart with minimal roof loads. Unlike with plywood siding the plywood sheet to be used for sheathing should be at least 3 8 inch thick.

A 1 2 sheet is actually 15 32 thick. Sheets of 7 16 inch thick with no edge support can be used in an area where the snow load is 30 pounds per square foot. With edge support and the same snow load 3 8 inch osb can be used. A roof that lays practically flat will have a much heavier load than a steeper roof that allows rain snow and ice to roll right off.

An exception to this standard however may occur if you intend to install slate concrete or tile shingles on your roof. This minimum will only work if the rafters are set 16 inches apart at most and if the roof doesn t have too much load. However you may need to consider bolstering the plywood thickness for a roof that has a higher load. In this case plywood should be a minimum of 3 8 inch thick.

Because the actual thickness may vary measuring the plywood is the only accurate way to determine its thickness. Loads will vary with the pitch of the roof. Most roofs will be sheathed in plywood at least 3 8 inch thick.