Roofing Plywood Over Boards

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.

Roofing plywood over boards.

If the old plywood had been removed. Today a shiplap roof is usually 60 years old. This particular type of plywood is crafted from layers of wood stacked on top of one another with alternating grain patterns in each layer. Applying the underlayment and the slip sheet.

Over time shiplap fir wood resin dissipates causing the boards to shrink crack form knot holes and become extremely brittle. If your home was built before 1970 there is an excellent chance that your roof is going to have board sheathing in place. 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. How to install metal roofing over plywood inspect your plywood.

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. It can withstand moisture for a brief period of time but may become warped and delaminated with consistent exposure to the elements. Plywood used for roof decking is typically called sheathing and. As the boards to do the roof deck were manufactured here in the northwest it was still more economical than plywood through the 60s.

Cdx plywood is a construction grade type of plywood that is designed for exposure to the elements. Most construction sites will consider the use of either osb or plywood for the roof. If the roofing underlayment is applied directly on top of the shiplap it will sag into the spaces and eventually leak. Most metal roofs will also require underlayment as well as a slip sheet.

After the 1960s the predominant residential roofing substrate became 1 2 cdx 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. Open spaces form between the once tightly fitted shiplap boards. Exterior grade plywood was not available until the 1940 s.