Adding a second layer could compromise your roof structure. Often, there is a problem with the first layer of tiles that was not evident before adding the second layer. Problems with the installation of a second layer of shingles begin with the installation. When you first install asphalt shingles, they are installed on a smooth, flat surface.
Adding a second roof doesn't have that option. Since the new layer is built on top of the previous one, it is built on a surface full of potholes and gaps. This makes the shingles more difficult to assemble precisely and safely. Over time, that will cause more and more problems.
Installing covers on the second layer of shingles is also incredibly difficult to do well. Without the right cover, the roof will leak and damage your home. When you only layer over the old roof, you won't have the same opportunity to fully inspect the roof covering. Buying a new roof may seem stressful, but adding new shingles over the old roof is not a good idea.
While your roof may appear structurally capable of supporting the additional weight, without an adequate view of the platform, there's no way to be sure. If you need to put a new roof on your home before you list it for sale, you may need to check with your home inspector or real estate agent. When you place new shingles on top of existing damaged roof tiles, you'll notice some strange imperfections or bumps that can get through your new roof. Adding an additional layer of shingles can have some drawbacks, such as reducing the lifespan of the roof, a possible negative inspection report, and destroying the aesthetic characteristics of the roof.
Home inspectors report the second layers of roofs to potential buyers, as well as the problems associated with multiple layers of tiles. That sounds like a lot, but with the exponentially greater likelihood of a roof problem occurring, nothing is saved in the long run. Once again, if you eliminate the entire stage of tearing (and cleaning) a roof, you'll save time. As you can see, there are far more disadvantages than advantages when it comes to overlaying a new asphalt shingle roof instead of tearing off the old one and replacing it.
With this extra weight, you can put your roof system at risk of sinking between the rafters, which can trap moisture and cause serious damage. If your home shows signs that your roof needs to be replaced, then you need to make some important decisions. The two most common reasons why you should add second-layer shingles to your roof are for convenience and affordability. That can cause serious problems in the future, especially when you consider the additional weight your roof would support with an additional layer of shingles.
This allows an accredited contractor to find any problems with your current roof and subfloor covering.