How Thick Roofing Plywood

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.

How thick roofing plywood. Loads will vary with the pitch of the roof. It is about 2 to 3 millimeters thick and is generally used indoors since it looks more decorative than thicker plywood boards. That will suffice on a roof with rafters set 16 inches apart with minimal roof loads. Although specialty plywood can have any number of plies above three most plywood is categorized as 3 ply 5 ply or multi ply.

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. 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. Unlike with plywood siding the plywood sheet to be used for sheathing should be at least 3 8 inch thick.

An exception to this standard however may occur if you intend to install slate concrete or tile shingles on your roof. In this case plywood should be a minimum of 3 8 inch thick. 3 ply is one of the most common types of plywood. Most roofs will be sheathed in plywood at least 3 8 inch thick.

Typical types of wood used for roof sheathing are oriented strand board known as osb and plywood the most popular being osb. 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. Plywood is often sold in 1 4 1 2 or 3 4 nominal thicknesses but the actual thickness is often 1 32 thinner. A 1 2 sheet is actually 15 32 thick.

Because the actual thickness may vary measuring the plywood is the only accurate way to determine its thickness. That s considered to be the minimum. That s considered to be the minimum.