Sheri, a homeowner in Washington state, had this question for our roofing experts:
What are the pros and cons of doing an overlay verses a tear out? (Besides the obvious savings in cost).
Our resident expert roofer, John Stout with Go Roof Tune Up™, had this to say in response:
Most roofers have lots of opinions regarding the pros and cons of reroof versus tear off. They also have opinions regarding the next president or which is the best pickup truck. In other words, there is no definitive, absolute answer.
Let’s start with the pro side. There is a definite cost savings. The labor cost to tear off the existing shingles is about equal to the labor cost to install the new shingles. It is not necessary to install felt underlay. There is very little clean up on a re-roof versus a tear off. Installing a roof over the roof eases the burden on the landfill. An added benefit during the rainy season is that installing shingles can be done between rainstorms without exposing the residence to water damage, unlike when the roof is removed. And an added benefit of leaving the existing roof on is it may be counted as R-Value when determining insulation requirements.
On the con side. Installing the roof over the existing roof adds considerable weight to the existing structure. Even with proper sized nails, shingles laid over shingles are susceptible to wind damage. The overall life of the new shingles is usually shorter than the average accepted life. One important advantage of removing the old shingles is to inspect and repair/replace damaged sheathing. If shingles are 30 years old and showing signs of leaking, there is a good chance that there is some sheathing damage that needs to be addressed. A fact that needs to be considered, in 30 years when the house needs to be reroofed again, there will be two shingle layers to remove instead of one. The cost for tearing off two roofs is about one and half times the cost of a single tear off.
It must be noted also that not all roofs can be recovered. Wood shake roofs cannot be roofed over. Tile or slate roofs cannot be roofed over. Compo shingles that are water soaked and badly deteriorated cannot be roofed over. Those types of roofs must be removed before applying new roofing.
I hope this information is helpful. One very important item that comes up when preparing for a new roof: replace sheet metal as necessary, including flashing and counterflashing, valley and edge metal. This is a necessary detail.
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