Your home's roof is the first line of defense against the outside world. If your home is showing signs that your roof needs replacement, then you have some major decisions to make. Most often your only option for new roofing is a roof replacement. Other contractors may have pushed an option to build a new roof on top of your existing roof. While it may seem like a worthwhile avenue and a chance to save money, there are many reasons not to have multiple layers of shingles.
The problems with installing a second layer of shingles start at the installation. When you first install asphalt shingles they're installed on a smooth, flat surface. Adding a "second roof" doesn't have that as an option. Since the new layer is built on top of the old one, it's built on a bumpy and gap-filled surface. That makes the shingles harder to accurately and securely mount. Over time, that will cause more and more issues. Installing flashing on the second layer of shingles is also incredibly difficult to do right. Without proper flashing, your roof will leak and damage your home.
Damage to the Roof
During the teardown of the old roof, a roofing contractor will usually inspect the area where your roof joins the rest of your house. This allows a reputable contractor to find any issues with your current roof decking and underlayment. Without this inspection, damage that your old roofing accrued will go unnoticed. The extra layer of shingles can also easily start leaks. With the increased chance of leaks, on top of possible damage that occurred previously, installing a second layer of shingles is asking for trouble.
That can lead to serious issues down the line, especially when you consider the extra weight your roof would hold with an extra shingle layer. Shingles can weigh between 350 and 450 pounds per 100 square feet. Your roof is designed to hold its own weight and the weight of snow. While your roof may structurally seem capable of supporting the added weight, without a proper look at the decking, there's no way to be sure. By adding a second layer of shingles, you're doubling what your roof has to hold. Most home builders and roofing contractors don't account for the added weight.
The main "benefit" of building a new roof on top of the old roof is the money you'll save. Immediately, you'd save the tear-off costs. That seems like a lot, but with the exponentially higher chance of a roofing problem, you aren't saving anything long-term. Having multiple layers of shingles also can bring down the value of your home. If you think you'd like to move, the second layer of shingles would make selling the house more difficult. House inspectors report second layers of roofing to potential buyers, as well as the problems associated with multiple shingle layers.
Summary - Reasons Not To Have Multiple Layers Of Shingles
Getting new roofing can seem stressful, but adding new shingles on top of your old roof is not a good idea. The reasons not to have multiple layers of shingles are that it makes installation more difficult and sloppy, it can seriously damage your roof and home, and proves more costly than just replacing your roof long-term. If you're interested in a roof replacement, call us today to schedule your free estimate or fill out our contact form and we'll be in contact shortly!