Roofing Plywood Over Boards

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.

Roofing plywood over boards.

Today a shiplap roof is usually 60 years old. The most common materials for this are oriented strand board osb or plywood both formed of layers of wood bonded into a panel. 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.

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. 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. Exterior grade plywood was not available until the 1940 s. Cdx plywood is a construction grade type of plywood that is designed for exposure to the elements.

This particular type of plywood is crafted from layers of wood stacked on top of one another with alternating grain patterns in each layer. If your home was built prior to 1970 there is a good chance it will have board sheathing. After the original roofing is removed what you will want to do first is look for bad pieces of. If the old plywood had been removed.

Most metal roofs will also require underlayment as well as a slip sheet. 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. As the boards to do the roof deck were manufactured here in the northwest it was still more economical than plywood through the 60s. 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 before 1970 there is an excellent chance that your roof is going to have board sheathing in place. Over time shiplap fir wood resin dissipates causing the boards to shrink crack form knot holes and become extremely brittle. Applying the underlayment and the slip sheet. Open spaces form between the once tightly fitted shiplap boards.