How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
Does a roof with multiple layers of shingles last longer?
Wednesday, July 11, 2018
While putting a new shingle roof over an older one seems to make sense because it might provide an extra of protection from the elements, a multiple-layer shingle roof actually creates more problems than benefits. The bottom layer (or layers) continue to deteriorate, becoming more brittle, buckling, and cracking underneath over time. It also creates additional dead weight on the roof and makes securely nailing the new roof shingles through the old ones more difficult.
Plus, to top it all off, leaving the old roof in place under a new one typically shortens the life of the top layer of shingles. And, because the old roof is not considered an acceptable substrate for a new roof by shingle manufacturers, any manufacturer’s warranty is voided. The only real benefit is a savings in labor and disposal fees for removal of the old roof shingles.
Also, see our blog post How can I tell if a roof has more than one layer of shingles?
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To learn more about roofs and attics, see these other blog posts:
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