Roofing Plywood Over Boards

How to install metal roofing over plywood inspect your plywood.

Roofing plywood over boards.

Cdx plywood is a construction grade type of plywood that is designed for exposure to the elements. Exterior grade plywood was not available until the 1940 s. After the original roofing is removed what you will want to do first is look for bad pieces of. 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.

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. Applying the underlayment and the slip sheet. Open spaces form between the once tightly fitted shiplap boards.

After the 1960s the predominant residential roofing substrate became 1 2 cdx plywood. 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. The most common materials for this are oriented strand board osb or plywood both formed of layers of wood bonded into a panel. This particular type of plywood is crafted from layers of wood stacked on top of one another with alternating grain patterns in each layer.

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. As the boards to do the roof deck were manufactured here in the northwest it was still more economical than plywood through the 60s. Most construction sites will consider the use of either osb or plywood for the roof. If the old plywood had been removed.

Today a shiplap roof is usually 60 years old. If the roofing underlayment is applied directly on top of the shiplap it will sag into the spaces and eventually leak. 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 prior to 1970 there is a good chance it will have board sheathing.