Plywood Over Old Roof

But with the old plywood left in place it will be considerably more difficult to locate the rafters to ensure proper nail.

Plywood over old roof.

If your home was built prior to 1970 there is a good chance it will have board sheathing. 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. Today a shiplap roof is usually 60 years old. Open spaces form between the once tightly fitted shiplap boards.

As the boards to do the roof deck were manufactured here in the northwest it was still more economical than plywood through the 60s. In the case of the old t g boards it makes for a flatter surface plus greatly lessons the chance of nailing into the gap between boards. 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. Another issue that many people encounter is what size plywood the roof may need.

Over time shiplap fir wood resin dissipates causing the boards to shrink crack form knot holes and become extremely brittle. The new plywood will have to be nailed to the rafters or roof trusses. Both cdx plywood and osb tend to come in standard sheets of four foot by eight foot 4 8. If the old plywood had been removed.

Its really common here too to see 3 8 plywood used on roofs from the 70 s. We resheet with 1 2 osb right over top of the old all the time be it 3 8 ply or old t g boards. After the 1960s the predominant residential roofing substrate became 1 2 cdx plywood.