Can a metal roof be installed over existing shingles?

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

Installing a metal roof over existing asphalt roofing reduces waste. Horch Roofing is dedicated to reducing the environmental impact of roofing waste in Maine (we recycle nearly everything), so if we’re simply installing a metal roof over the existing roof, there’s little to no excess roofing waste.

Standing seam metal 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 metal over an existing asphalt roof can save you money by eliminating the removal and disposal costs.

Most local roofing contractors and manufacturers agree that installing a new standing seam metal 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. Your sales estimator can discuss the best options for your specific project.

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.

There are drawbacks to not stripping off the old asphalt roof prior to installation of a standing seam metal roof. There is no opportunity to inspect the roof deck or rafters for damage or rot, or to address any existing roof leaks. You also need to be aware of any signs of the previous roof weighing too much. Signs may include buckling tresses or sagging decking. If you have concerns about the structural integrity of your roof they should be addressed before installing a “lifetime” roof system. Your knowledgeable Horch Roofing sales estimator can walk you through the process and discuss the best options for your home.

Horch Roofing is Maine’s trusted roofing contractor. We have been roofing homes from Kittery to Castine since 2003 and serve the communities of Maine from our offices in Warren and South Portland. We have a dedicated Northern Maine sales estimator serving Hancock County and Bar Harbor. Horch Roofing installs Standing Seam Metal Roofing, Asphalt Shingle Roofing, EPDM Rubber Roofing, and Seamless Gutters for both residential and commercial roofing projects. We offer free roofing and gutter replacement estimates. You can call us at (207) 273-1111, or contact us online.