How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
How can I tell if a roof has more than one layer of shingles?
Sunday, June 24, 2018
Adding a new second layer of shingles over an existing shingle roof is called a “roof-over” in the construction industry, and it does have a couple of advantages:
- The cost of removal and disposal of the old roof is eliminated.
- It has been required in Florida for about the past decade that any new roof installation must have the roof sheathing re-nailed with 8d (eight penny) nails at a closer spacing than previously required. This is not necessary for a roof-over, and saves a homeowner more money.
But the downside is that a roof-over typically does not last as long as a roof replacement and, when you do replace it, the tear-off and disposal of two layers of shingles costs extra. A maximum of two layers of shingles is allowed by the building codes. Plus, you have to do the re-nailing that was put off by the previous roof-over.
One clue that a home has had a roof-over which is easily observable from the ground is that it looks a little lumpy overall, but especially at the roof penetrations, like plumbing vents and gas appliance flues. The photo above of a plumbing vent at a roof-over is a good example.
And here’s another example at furnace flue. Notice the waviness at the ridge also.
The way to be sure you are looking at a double layer of shingles is to get up on a ladder (if you are comfortable doing that) and examine the shingles at the edge. A normal roof has a “starter” row of shingles and then a single layer above it, for a total of two layers of shingles. A roof-over will have four layers, like in the photo below.
Also, see our blog post Are two layers of shingles better than one?
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To learn more about roofs and attics, see these other blog posts:
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