Sometimes. Building codes generally allow a new roof over one existing layer of shingles, but not over two or more layers. Even when it’s allowed, we usually recommend tearing the shingles off so the decking can be inspected and repaired, and the metal can be installed over a clean, flat surface.
What the code says
Under the International Residential Code, which Tennessee and Mississippi communities adopt with local changes, the old roof must be removed if it already has two or more layers of roofing. A roof can also need a tear-off if the existing roof or decking is water-soaked or deteriorated. Your local building department has the final word for your address.
Why tearing off is usually the better choice
- You can see the decking. Rotted or soft wood hides under old shingles. Covering it means fastening a 50-year roof to wood that may not hold.
- Fewer surprises later. Old shingles can trap moisture and hide leaks that keep doing damage under the new roof.
- A flat surface. Metal panels show waves and bumps from uneven shingles beneath them.
- Warranty requirements. Manufacturer installation requirements can affect what is allowed over an existing roof, so check the warranty terms for the panel you choose.
How over-shingle installs are done
When metal goes over shingles, installers commonly screw wood strips (purlins) across the old roof and fasten the metal to those. It saves the cost of tear-off, but it adds a layer that hides the deck for the life of the roof.
Our approach
We’ll inspect your roof and tell you what we find before you decide. Learn more about roof replacement or why we recommend removing the old roof.
By the numbers
- 2021 IRC R908.3: the existing roof must be removed when it already has two or more applications of roof covering.
- A metal roof can last 40 to 70+ years (MTR cost guide), so the decking under it needs to last that long too.
Thinking about metal for your home? Schedule a roof inspection or call (901) 834-7663, and we’ll tell you whether metal makes sense for your roof.
