Should You Install a Metal Roof Over Old Asphalt Shingles?
Metal roofs provide a durable, long-lasting, and low maintenance alternative to asphalt shingles, but the initial installation can be more costly. One way to reduce this cost is to use the old asphalt shingles as the base for the new metal panels.
What Benefits Do the Old Shingles Provide?
There are many good reasons to leave your old asphalt shingles in place when installing a new metal roof. The most obvious is reduced labor costs since the crew won't have to tear off and dispose of the old shingles. The old shingles also provide another layer of weather resistance beneath the new roofing material.
Are There Any Local Building Restrictions?
Most states and municipality building departments allow one layer of old shingles to remain under a new metal roof. As long as the previous asphalt shingles weren't a reroofing job, which means new asphalt was installed over a layer of old asphalt shingles, you can leave the old shingles in place. Make sure to verify with your building department before proceeding, though.
What is the Quality of the Existing Shingles?
The quality of the old roof must also be considered. If the plywood sheathing beneath the shingles requires extensive repairs or replacement, the old shingles will have to be removed. Otherwise, your metal roof installer can locate any damaged shingles and repair them after verifying that the sheathing beneath is in good condition. An attic inspection of the sheathing can help your roofer make the right decision.
Is an Underlayment Necessary?
Shingles that are degraded or damaged can still be left in place if the sheathing is in good condition, but there will be some concerns with weatherproofing. For this reason, your roofer will likely recommend installing a layer of underlayment over the shingles for added protection. A layer of tar paper or another suitable roofing underlayment will ensure that your new metal roof remains free of leaks.
Are There Any Potential Issues to Watch For?
Issues with leaving the old shingles in place can often be avoided with a bit of prep work. The biggest problem is if the shingles are wet. For this reason, your roofer will likely advise cleaning the roof several days in advance of the metal roof installation if there is moss or debris collected on top of the shingles. This ensures that the shingles have plenty of time to dry out before the metal roof goes on. Other than this moisture issues, as long as the sheathing isn't damaged there are few issues to worry about.
Contact a metal roof install service if you have further questions.
