Roofing Plywood Over Boards

If the old plywood had been removed.

Roofing plywood over boards.

Open spaces form between the once tightly fitted shiplap boards. Most metal roofs will also require underlayment as well as a slip sheet. Exterior grade plywood was not available until the 1940 s. As the boards to do the roof deck were manufactured here in the northwest it was still more economical than plywood through the 60s.

If your home was built prior to 1970 there is a good chance it will have board sheathing. Most construction sites will consider the use of either osb or plywood for the 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 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. After the 1960s the predominant residential roofing substrate became 1 2 cdx plywood. Today a shiplap roof is usually 60 years old. 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. The most common materials for this are oriented strand board osb or plywood both formed of layers of wood bonded into a panel. After the original roofing is removed what you will want to do first is look for bad pieces of. How to install metal roofing over plywood inspect your plywood.

Applying the underlayment and the slip sheet. It can withstand moisture for a brief period of time but may become warped and delaminated with consistent exposure to the elements. If the roofing underlayment is applied directly on top of the shiplap it will sag into the spaces and eventually leak. This particular type of plywood is crafted from layers of wood stacked on top of one another with alternating grain patterns in each layer.