New Plywood On Top Of Old Plywood On Roof

Like most other things there is no one right answer for the plywood thickness of your roof.

New plywood on top of old plywood on roof.

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. Until the 1940s exterior grade plywood was not available. If the old plywood had been removed. Chances are the shingles on your roof were attached on top of a plywood base.

The most common scenario is a home that has rafters set approximately 16 inches apart. This is the best product to use because its very sturdy and high quality. If there is water damage it will preform significantly better than the 1 2 plywood. 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.

But with the old plywood left in place it will be considerably more difficult to locate the rafters to ensure proper nail. 5 8 inch 26 87 per sheet. The new plywood will have to be nailed to the rafters or roof trusses. Since the boards used for shiplap were manufactured here in the pacific northwest it was still cheaper than plywood up through the 1960s.

Sometimes referred to as roof sheathing or a roof deck this plywood acts as a foundation for the layers of underlay and the shingles on your roof and connects the roof to the frame of the house. This means that you must replace old roofing plywood. So now they install 3 8 plywood over the top of whatever crap is in place so that the owner sees a new roof and they can stick the i w along the eaves and valleys and have it work. While they don t prohibit installation over board sheathing asphalt shingle manufacturers do specify that the roof deck underneath must be smooth and tend to recommend plywood as the best option.

One reason often cited by contractors to justify adding a layer of plywood to an existing roof structure is the presence of old style board sheathing. Here is approximately how much different options cost.