Below is what our roofing expert John Stout from Go Roof Tune Up
had to say in response to your question:
“Most roofers have lots of opinions regarding the Pros and Cons of Reroof vs. 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 under lay. There is very little clean up on a re-roof vs. a tear off. Installing the roof over roof eases the burden on the landfill. An added benefit in the raining season, is installing shingles can be done between rainstorms without exposing the residence to water damage if the roof would be removed. 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 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 are 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 2 shingle layers to remove instead of one. The cost for tear off of 2 roofs is about 1 ½ times the cost of 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: it is very important to replace sheet metal as necessary. Include flashing and counterflashing, valley and edge metal. This is a necessary detail.
Thank you for your question. Consult RoofersCoffeeShop
for a list of qualified contractors in your area to roof your house.”