Plywood Over Old 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.

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. If the old plywood had been removed. Open spaces form between the once tightly fitted shiplap boards. Today a shiplap roof is usually 60 years old.

The new plywood will have to be nailed to the rafters or roof trusses. Its really common here too to see 3 8 plywood used on roofs from the 70 s. Over time shiplap fir wood resin dissipates causing the boards to shrink crack form knot holes and become extremely brittle. However you might find that osb can better suit your needs than plywood for the roof.

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. 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. After the 1960s the predominant residential roofing substrate became 1 2 cdx plywood.

Both cdx plywood and osb tend to come in standard sheets of four foot by eight foot 4 8. Fortunately this is one issue that has primarily been standardized by the industry. 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.