Roofing Plywood Over Boards

Cdx plywood is a construction grade type of plywood that is designed for exposure to the elements.

Roofing plywood over boards.

Plywood used for roof decking is typically called sheathing and. Most construction sites will consider the use of either osb or plywood for the roof. Open spaces form between the once tightly fitted shiplap boards. Applying the underlayment and the slip sheet.

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 and roof. With the boards to do the decking being manufactured in the northwest it was a lot more economical to use these boards than it was plywood at least through the 1960s anyway. If the old plywood was clean and not infested with dry rot or mold it should be ok to cover it with the new plywood. One thing to consider is that the new plywood probably wants to be the same thickness as what would be used if it was used by itself on the rafters i e.

This particular type of plywood is crafted from layers of wood stacked on top of one another with alternating grain patterns in each layer. It can withstand moisture for a brief period of time but may become warped and delaminated with consistent exposure to the elements. If your home was built prior to 1970 there is a good chance it will have board sheathing. Over time shiplap fir wood resin dissipates causing the boards to shrink crack form knot holes and become extremely brittle.

Most metal roofs will also require underlayment as well as a slip sheet. How to install metal roofing over plywood inspect your plywood. After the 1960s the predominant residential roofing substrate became 1 2 cdx plywood. Exterior grade plywood was not available until the 1940 s.

The most common materials for this are oriented strand board osb or plywood both formed of layers of wood bonded into a panel. If your home was built before 1970 there is an excellent chance that your roof is going to have board sheathing in place. Today a shiplap roof is usually 60 years old. If the old plywood had been removed.