Can A Metal Roof Be Installed Over Existing Shingles?

By Peter Horch | Feb 14, 2018

We’re often asked whether it’s possible to install a metal roof over an existing shingle roof. The short answer is yes; here are a few things to consider.

Installing a metal roof over existing asphalt roofing reduces waste. Horch Roofing is dedicated to the environment and waste management (we recycle nearly everything), so if we’re simply installing a metal roof over the existing roof, there’s little to no waste.

Metals roofs are more expensive than asphalt, but they can last as long as 50 years, at least twice as long as an asphalt-shingle roof. Installing over an existing asphalt roof can save you money by eliminating the removal and disposal costs.

Most roofers, contractors, and manufacturers agree that installing a new roof over one layer of old roofing is safe and can still carry a manufacturer’s warranty. That being said, most manufacturers along with local and national building codes suggest that no more than two layers of roofing be allowed on a roof.

The primary method for installing a metal roof over asphalt is to fasten a synthetic underlayment atop the existing shingles and then lay the metal roof over that. This synthetic underlayment acts as a vapor barrier and a “slip sheet.” The slip sheet allows the metal roofing to expand and contract without damaging the finish coating on the underside of the panels. This method ensures the longest life out of your new metal roof after being installed over existing shingles.

For answers to more roofing questions or to get an estimate on installing a metal roof, contact Horch Roofing at (207) 273-1111.

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