During our home inspections, we often see more than one layer of roof shingles. In fact, sometimes we see 3 or 4 layers of roofing materials which can cause several problems.
1) Most roof shingle manufacturers will not honor their warranty if there is more than a single layer of roofing shingles.
2) Most building codes do not allow a 3rd layer.
3) The 2nd and 3rd layers of roofing shingles are prone to blowing off in the wind.
4) Shingles have a shorter lifespan due to overheating from the sun.
5) having more than one layer impacts the aesthetics.
6) In addition, roofing materials are very heavy and could easily add up to 10,000 pounds on an average sized roof which puts additional stress on the roof rafters which ultimately translates all the way down through the framing of the house and to the foundation.
7) And very importantly, unless all the shingles are removed, the condition of the roof sheathing (the wood below the shingles) can’t be observed, so consequently, there may be deteriorated roof sheathing that should be replaced but can’t. Occasionally, someone falls through the roof because the wood under the shingles is completely deteriorated due to long term water leakage.
8) most inspectors will comment that a 2nd or 3rd layer of shingles is a negative condition.
There are some advantages to going with a second layer of roofing material: it’s cheaper, and a bit faster. But taking the pros and cons into consideration, the benefits of keeping a single layer of roofing far outweighs the cons.
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