New Roof Sheathing Over Old

Why installing new shingles over old shingles can be good.

New roof sheathing over old.

Installing new roof shingles over old effectively doubles the weight of the roofing so you have to make sure your roof structure can handle the extra load. If conditions are right new shingles laid over old shingles can be just as attractive and durable as shingles laid on bare sheathing. Let s start with the good. When roofing over your existing shingles can be a good idea.

Its really common here too to see 3 8 plywood used on roofs from the 70 s. Gable end detail overhang cut and then rebuilt to hide the thickness of the over roofing rigid insulation. That s also why building codes commonly limit re roofing to no more than two layers. Installation is easier than for a tear off job because you can use the existing shingles as guides for laying the new ones.

Roy gingrich of ellicott city has a 40 year old house with an asphalt shingle roof surface. You can save money because there s no dump fee for removing your old roofing and there s no need for additional felt paper over the old roof. Many arizona homeowners with shingle roofs do decide to roof over their existing shingles because. If your roof is in good shape but has some damage to one side from a downed tree or has lost shingles in a wind storm an overlay is worth considering.

But you must take care to install shingles correctly so they lie flat. Roof edge detail overhang extended to hide the thickness of the over roofing rigid insulation. Nailing new shingles over existing ones is less expensive and faster requiring less labor but it also means you lose the chance to assess the sheathing for signs of water damage. As long as the new plywood itself can span the distance and carry the roof wind seismic and snow loads for your region adding new ply over old is just fine.

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 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. The new plywood thickness should be.