However there is no easy universal answer if only one roof is in place.
Roof strip and replywood.
In some cases local building codes will limit the available options most do not allow more than two roof coverings on a building.
Building codes say you can put a second layer of shingles over the first layer but it s better to strip off the old shingles and start with a clean slate.
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When used for roofing plywood panels are covered and protected by a variety of building materials that keep the elements at bay including roof felt underlayment flashing and shingles.
There s anecdotal evidence that new shingles installed over old shingles won t last as long as a single layered roof most manufacturers offer the same warranty for both methods.
Loads will vary with the pitch of the roof.
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The process of removing the existing roof covering repairing any damaged substrate and installing a new roof covering.
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Most roofs will be sheathed in plywood at least 3 8 inch thick.