Why It’s Bad To Put Metal Roofing Over Shingles

Installing metal roofing over shingles can lead to more problems down the road for your house
Read Time: 5 minutes
Dec 19, 2022

Getting a new roof can be very costly, but it’s often necessary. An old or faulty roof will leave you and your house unprotected and vulnerable to further damage. However, many people understand that they need a new roof, but do not want to go through the entire process of replacing it. So instead, they choose to put a metal roof over their asphalt shingle roof, thinking it can save them time and money.

Unfortunately, this choice is not smart in the long run. Let’s break down why.

There’s No Chance to Inspect Underneath

A close-up of roof decking that has rotted, with a large hole and water damage.

If you simply put a metal roof on top of your asphalt shingle roof, you and your contractors won’t get to see what’s underneath the shingles. Most roof problems occur underneath the first layer. If there’s a problem with the roof, you won’t know before putting another roof on top of it. Here are some of the things that you could find if you took off the original roof instead:

Faulty Roof Decking

Roof decking is made up of wooden boards that form the foundation of your entire roof system. Typically, if you wanted to replace a roof, you’d rip everything down to the decking to see if there is anything wrong with it, such as broken boards, rotting, or mold. Roof decking problems are fairly common. But if you don’t take a look at the decking, you won’t know if the decking can even handle the new roof.

Elements That Need Replacing

Men on a roof install underlayment, a layer that goes on top of the roof decking.

When you cover up the first roof with a metal roof, you can also miss finding crucial roofing elements that need to be replaced. Not taking the time to see what elements need replacing is dangerous. For example, your underlayment might need to be replaced. Underlayment goes over your decking as the roof’s last line of defense. Most metal roofs use a special underlayment designed specifically for metal roofs. But without removing the asphalt shingle roof, you won’t be able to put in that special underlayment.

It Adds to the Weight of the Roof

Installing a metal roof on top of a shingle roof is also problematic because of the extra weight you’ll be adding. If you haven’t looked properly at your roof’s decking, it’s hard to know if the roof can even handle that extra weight. Adding extra weight to your roof can do structural damage to both your roof and your home over time. Even if the problem does not appear immediately, you may notice problems in the future.

It’s Harder to Find Future Leaks

A bucket on the floor collects water from a spill up above.

If you install a metal roof over a shingle roof, it could be harder to find and fix leaks in the future. Down the road, when you get a leak in your roof, you won’t know where it’s coming from: the first roof or the metal roof. Not only does this make it harder to find, but also harder to fix. In the case that the leak is coming from the original shingle roof, a contractor will have to go through the metal roof to repair it.

It Covers Up Problems

A man uses a crowbar to fix a roof that has rotten wood.

If there’s anything wrong with your old roof, putting a metal roof on top of it will just cover up the problems rather than solve them. For example, if there is mold or mildew within the first roof, putting a new roof on top of it will only cover up the problem for a while. But the mold will continue to spread underneath the metal roof, causing damage to your house and potentially your health.

It Can Create an Uneven Surface

When placing a metal roof on top of a shingle roof, most contractors use furring boards as the foundation between the two. But because shingle roofs aren’t flat to begin with, the furring boards can create an even more uneven texture for the metal roof to sit on top of. Additionally, they can absorb the humidity and warp over time.

It’s Not Allowed Everywhere

Installing a new roof on top of an old roof isn’t allowed everywhere. Some counties and jurisdictions have building codes prohibiting the practice because it can be dangerous and cause long-term damage to the residence. So if you are still considering putting a metal roof over a shingle roof, you should contact your local government first.

It Can Shorten the Roof’s Lifespan

Because of all the problems that can occur when putting a metal roof over a shingle roof, the roof’s lifespan can shorten. Adding extra weight and making your roof vulnerable to more water damage can mean you’ll end up replacing your roof earlier than anticipated.

Why Install a Metal Roof?

Two workers in hardhats install sheets of red metal roofing on top of a roof.

Metal roofs have many benefits when they’re installed properly. These include:

Energy Efficiency

Metal roofs reflect sunlight and heat in the summer, keeping your home cooler. As a result, you can use less energy for air-conditioning.


Most metal roofs are fire-resistant, so they can make your home safer when installed properly.


When you install a metal roof the right way, it can last for over 50 years. This durability is one of the leading causes of metal roofs’ recent popularity.

Different Styles and Colors

Metal roofs come in many different styles, colors, and textures, so you can choose one that matches your home’s exterior perfectly.

Very Lightweight

Metal roofs are very lightweight compared to asphalt shingle roofs. They aren’t as much of a structural liability as shingle roofs unless they’re installed on top of one, of course.

Have more roofing questions?

Speak with our roofing experts.

Contact us