Install a metal roof over shingles
If you decide to install a metal roof over shingles, you should be aware that if you have multiple layers of shingles to cover, the application may not work.
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A metal roof is an alternative to asphalt shingles. In some instances, it can be installed over an existing shingle roof. If you decide to install a metal roof over shingles, you should be aware that if you have multiple layers of shingles to cover, the application may not work.
The most obvious reason that you might want to install a metal roof over shingles is that you won't have to worry about the work and costs of removing the old shingles. Roofing prices are expensive as it is, so this can be appealing. However, this type of installation has some drawbacks that you should consider.
First of all, when you simply cover up shingles that are deteriorating anyway, the shingles are still there, and they will continue to deteriorate. The existing shingles will still lift and cup, and this can compromise the lap joints.
The continued deterioration can also cause the fasteners to begin leaking. As a result, you can end up with more problems than you currently have with your roof.
If your existing shingle roof is in poor condition, any shingles that are heavily degraded or cracked will need to be removed. When you're determining whether you can install metal roofing over your current roof, keep in mind that the roof decking beneath the shingles must be in good condition and solid enough to support the weight of the metal roof for the long term. You will need to undertake roof repair on the existing roof if it is not up to par.
The second layer can also act as a vapor barrier. Water vapor can become problematic. This can lead to a buildup of vapor that can cause rot and mold. Due to this very real concern, you will need to talk to your roofer about using materials that are specially vented to curtail the issue.
Additionally, the metal roof can be installed on top of furring strips. These strips will raise the metal, providing a pocket of air between the shingles and the metal.
Even when a proper ventilation plan is in place, you may not be able to install a metal roof over shingles if your local building codes will not allow it. Many local codes forbid this type of installation, because the weight of the metal roof in addition to the existing shingle roof is too great.
Roofing trusses can accommodate up to 10 pounds per square inch. If you have multiple layers of shingles, adding metal to the roof may cause the roof trusses to fail, posing a safety concern. Even if you take this precaution, however, such an installation might void any metal roofing warranty that you might have enjoyed with a regular installation.
The obvious upside to trying to install metal over your existing shingles is that it will save you money. It can also provide a sound and vapor barrier between the metal and the attic.
One reason that many people choose to put metal over shingles is to prolong the life of the shingles. Shingles can be and often are recycled, but in places where that’s not possible, this can be a way to keep the shingles out of a landfill and reuse them for a longer period.
The cost savings, energy benefits, and environmental benefits all make this a question to ask a roofing contractor when they are looking at bidding your roof replacement.
An expert roofing contractor will know how to install a metal roof over shingles, including composition and asphalt shingles. Reply! is a great resource for finding local residential roofing professionals who can provide you with a roofing estimate to install a metal roof over shingles and who can discuss roofing cost concerns with you.
Photo credit: Everlast Roofing