Plywood Over Old Roof

Today a shiplap roof is usually 60 years old.

Plywood over old roof.

If the old plywood had been removed. The new plywood will have to be nailed to the rafters or roof trusses. 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. Both cdx plywood and osb tend to come in standard sheets of four foot by eight foot 4 8.

Exterior grade plywood was not available until the 1940 s. After the 1960s the predominant residential roofing substrate became 1 2 cdx 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. Its really common here too to see 3 8 plywood used on roofs from the 70 s.

Another issue that many people encounter is what size plywood the roof may need. However you might find that osb can better suit your needs than plywood for the roof. If your home was built prior to 1970 there is a good chance it will have board sheathing. But with the old plywood left in place it will be considerably more difficult to locate the rafters to ensure proper nail.

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. Fortunately this is one issue that has primarily been standardized by the industry. Open spaces form between the once tightly fitted shiplap boards.