When a typical 3-tab asphalt roof needs replaced, roofers will often go over the existing layer of shingles with the new layer. It’s common to see roofs with two or even three layers of shingles; but while this may seem advantageous, it is actually not the preferred method for installing a new roof.
You would probably assume that leaving the old layer of shingles in place is a good idea since it may act as another layer of protection against water. In reality, though, the downsides of keeping the old layer outweigh any possible benefits. Leaving the old layer in place adds extra weight to the roof and increases heat, thus decreasing the life of the new layer on top.
It is more work for the roofer and more money for the homeowner to do things properly, but as is usually the case, the harder way is the best way. If your asphalt roof needs replaced, the old layer of shingles should be completely removed. This exposes the wooden roof decking (sheathing) and allows the roofer to make any necessary repairs to the wood to ensure a solid base for the new layer of shingles. It also makes the entire installation process of the new shingles easier and cleaner. The proper method guarantees that the weight on the roof is kept as low as possible and that the shingles are not subjected to unnecessary adverse conditions that will decrease their useful life and, thus, your investment. After all, roofs aren’t cheap!
Removing the old layer of shingles adds quite a bit of extra work, which increases labor costs. There are also additional fees for hauling away and dumping the old layer. Still, it’s worth it in the long run to do things right.
If your roof currently has two layers of shingles, it’s no cause to panic. Just be sure that when you end up needing to have a new roof installed in the future you instruct the roofing contractor to remove all layers and repair any damaged roof sheathing before installing the new roof. Years after, you’ll be very glad that you paid more for a job well done and that your new roof will likely last longer than if you had taken the easier, less costly route.
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