Roofing Plywood Over Boards

If your home was built prior to 1970 there is a good chance it will have board sheathing.

Roofing plywood over boards.

Most metal roofs will also require underlayment as well as a slip sheet. 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. 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. Applying the underlayment and the 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.

Open spaces form between the once tightly fitted shiplap boards. The most common materials for this are oriented strand board osb or plywood both formed of layers of wood bonded into a panel. 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.

If the old plywood had been removed. 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. 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.

After the original roofing is removed what you will want to do first is look for bad pieces of. Most construction sites will consider the use of either osb or plywood for the roof. Exterior grade plywood was not available until the 1940 s. How to install metal roofing over plywood inspect your plywood.