How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
How many layers of roofing are allowed on a home?
Wednesday, August 1, 2018
You are allowed to put one additional layer of roofing over an existing roof, which is called a “reroof”; but, once there are two layers of roof, you must strip off both layers down to the deck the next time you need a roof, which is a “roof replacement.” This applies no matter what type of roof you install.
The primary issue that causes the International Residential Code to have this limitation is the added weight of an additional roofing layer. An architectural shingle roof, for example, weighs about 100 pounds per square—a roofer’s term for 100 square feet of roof surface. Any areas of damage or imperfections in the bottom layers of roofing will telegraph through to the upper layer and, as you exceed two layers, securely nailing the top layer through the bottom ones also becomes problematic.
We have been told that in some jurisdictions the local building official can authorize installation of more than two layers of roofing. However, we have never heard of it done in our area.
Want to know how to recognize a multiple layer roof? They are easy to spot if you know what to look for. 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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