Can you install a metal roof over existing shingles?
Absolutely you can! Installing a metal roof over existing shingles rather than tearing the shingles off can have many benefits. However, before you can begin laying your metal, you should first inspect the existing roof to ensure it has the proper conditions to support a metal roof. You must also understand how to install over shingles.
1. Preparing/Inspecting the Existing Roof
Before installation, you should consider the condition of your shingles. According to Metal Roofing University, "If your current shingle roof has sustained significant damage or has begun curling then you should either remove it or install lathing boards before installing a new metal roof (assuming the roof deck is in good condition)." Undamaged, non-curling shingles will provide the best, most planar conditions for your metal roof to be installed. Neglecting to repair or replace shingles accordingly could cause damage anywhere from oil-canning effects to metal roofing system failure.
In addition to the condition of your shingles, you should consider how many layers of shingles you have. Consult your building code before adding a metal roof over your shingles, as most codes do not allow for more than two layers of roofing materials on your roof.
Inspect your roof deck for fire, water, hail or any other kind of damage before proceeding with the metal roof installation. Remove shingles where necessary and repair/replace the roof deck areas as needed. This will prevent larger, more costly issues from arising after the metal roof has been installed.
Leaving shingles on your build before adding a metal roof will result in more weight. If the trusses were not designed to support the extra weight, you could potentially see long-term concerns such as sagging or broken trusses. However, metal roofs are typically lightweight in comparison to shingles. So, just be sure the weight load will not jeopardize the structure's integrity. If you need assistance, consult your post frame builder. (FBi Buildings)
Photo from Metal Roofing University
2. How to Install
Before you can install your metal roof, you must first install wood furring strips or spacers. "Metal roofing expands and contracts as it heats up and cools down (thermal expansion). If left to constantly move against the abrasive grit on asphalt shingles you may introduce a scenario where the primer on the back of your metal roofing panels is scratched off exposing the panel's substrate and creating an environment for rust to occur," (Metal Roofing University). MWI's Labor Saver is a great tool for reroofing with ease. Wood spacers can warp (causing creased roof panels), rot or even corrode; plus, they are a bit unrealistic. The Labor Saver is much lighter (yet durable) and easier to store, it won't corrode metal or shingled roofs, and it can simply be rolled across your roof and tacked down.
3. Benefits of Installing a Metal Roof Over Shingles
If you've done your homework, installing a metal roof over shingles should have benefits. Regardless, metal roofs have the ability to last a lifetime; however, installing over existing shingles gives you another layer of protection between the elements and the inside of your building. Also, the extra layer of shingles will aid in sound absorption - minimizing rain or hail reverberation on the metal roof. Finally, you will save a great deal of time and a substantial amount of money in labor costs by not tearing off your existing shingles.
All in all, reroofing with metal panels over your existing shingles can have great benefits, but it is essential to inspect, repair where necessary, and ensure your building's structural integrity will not be compromised.
For more info on reroofing over existing shingles, check out these articles:
https://www.metalroofingu.com/post/can-you-install-metal-roofing-over-shingles (primary resource) or https://rimainternational.org/myths/faqs/ (secondary source). Meanwhile, take a closer look at our Labor Saver by clicking here!