Roofing Plywood Over Boards

Applying the underlayment and the slip sheet.

Roofing plywood over boards.

Plywood used for roof decking is typically called sheathing and. If your home was built before 1970 there is an excellent chance that your roof is going to have board sheathing in place. After the 1960s the predominant residential roofing substrate became 1 2 cdx plywood. 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. Cdx plywood is a construction grade type of plywood that is designed for exposure to the elements. Open spaces form between the once tightly fitted shiplap boards. 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 prior to 1970 there is a good chance it will have board sheathing. 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. How to install metal roofing over plywood inspect your 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. 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. This particular type of plywood is crafted from layers of wood stacked on top of one another with alternating grain patterns in each layer. Most construction sites will consider the use of either osb or plywood for the roof.

As the boards to do the roof deck were manufactured here in the northwest it was still more economical than plywood through the 60s. After the original roofing is removed what you will want to do first is look for bad pieces of. 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. If the old plywood had been removed.