Should I tear off my old roof or just roof over it?
Complete removal of the existing roof system is mandatory if it contains moisture, or if the
additional roof layer exceeds safe load design, or if local codes require that the existing roof
be removed. Most local codes will only allow two layers of 3-tab shingles.
A second layer of shingles can be installed over Dimensional / Architectural style shingles, as
the weight would meet most local code requirements.
Installing shingles over an existing roof system requires proper preparation of the surface.
Blisters, splits and other roof membrane or flashing defects should be repaired in accordance
with good roofing practices to attain a surface which is smooth, dry, clean and free of sharp
projections and depressions. If the roof is not smooth and flat, the flaws will project and be
seen through the new roof.
Finally, the service life of the new shingles should be considered. The U.S. Department of
Housing and Urban Development performed a study which concluded that as much as 25% of
the service life of the new shingles will be lost when installed over an existing layer of shingles
due to heat retention.
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reproductive harm are
created by the combustion
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