Can You Install a Metal Roof Over an Asphalt Roof?

So, you want to upgrade your current asphalt roof to a new metal roof, but you're on a tight budget. After some research or talking to a contractor, you've probably heard the possibility of installing a metal roof over your existing asphalt roof.

But is this a good idea? Because we want you to have all the important information about such a big decision, we're going to break it down for you. 

The team at Bill Ragan Roofing has been providing the residents of Nashville with high-quality asphalt and metal roofs since 1990. We know what it takes to maximize the life of your roof. That’s why we offer a lifetime warranty on our workmanship. 

By the end of this article, you'll learn if it's a good idea to install a metal roof over an existing asphalt roof and some warnings about doing so. And if you're still on the fence about which type of roof to choose, we developed a free quiz to help you even further.  

The common residential roof types: asphalt and metal

Before we get to if you can install a metal roof over an asphalt roof, you need to know a little about both. 

Asphalt roofing

There are three types of asphalt roofs: 3-tab, dimensional, and luxury. While 3-tab used to dominate the market, dimensional shingles are the most common type installed on roofs today. 

Luxury style shingles are just as heavily marketed as dimensional but are almost double the price. To learn more about the asphalt shingle roofs, read this article on the 3 types of asphalt shingles.

Metal roofing

There are two types of metal roofs, a standing seam and a screw-down panel. A standing seam metal roof system is a series of panels that are locked together at the seams or seamed mechanically. This allows for panels to expand and contract freely when the metal heats up.

A screw-down panel is just what it's called; it's screwed down. The screws are screwed through the panel, which leaves no room for expansion and contraction. I would not recommend putting a screw-down panel over a heated space such as your home or office due to its lack of expansion capability.

To learn more about the two metal roof systems, read this article on metal roofs: standing seam vs. screw-down panel. 

Can you install a metal roof over your existing asphalt roof?

So, can you install a metal roof over your old asphalt roof? 

The short answer is yes, you’re able to roof over your old asphalt roof with a new metal roof under the right circumstances. Your current asphalt roof has to be near the end of its lifespan and still lying down pretty flat (no lifted or cracked shingles, blisters, or bumps). With that in mind, most roofs won’t be good candidates because of the wear and tear they go through during their lifespans. 

As long as the new metal roof is properly installed and your local roofing contractor does everything the right way, it can be done without a problem. You’ll be able to save up to 25% in labor costs by not tearing off your old asphalt roof, installing new underlayment, or the fees to dump the old roofing materials.  

So, yes, you can install a metal roof over your old asphalt roof. However, I wouldn’t recommend it. 

Because I don't recommend it, you need to know how the two types of roofs compare to each other on important factors so you can decide which one fits your needs.

3 warnings when installing a metal roof over an asphalt roof

Why wouldn’t a reputable roofing contractor recommend installing a metal roof over your old asphalt roof? There are a few reasons, below you’ll learn the 3 warnings of roofing over your old asphalt roof with a metal roof. 

1. Your decking is covered up by your old asphalt roof

Decking is the wooden boards that make up the framing of your roof. These boards are what your roof and other components are installed on.

When you get a full roof replacement, your old roof is torn down to its decking. This gives your contractor a chance to inspect the decking’s integrity to see if it can handle your new roof.

If you install a metal roof over your asphalt roof, there’s no opportunity to inspect your roof’s decking. If your contractor can’t test your decking’s integrity or inspect for rotten boards, it could lead to a costly problem down the road. 

I understand everyone is on a budget, but if you’re investing in a metal roof you might as well tear-off your old asphalt roof to avoid this problem.

2. Future roof leaks will be harder to track 

Your leaky asphalt roof is covered up without taking care of the problem when you put a metal roof over it. Once water gets under your metal panels, it’ll run down and across your old asphalt shingle roof. 

The water will keep running until it gets to problem areas and starts to leak inside your home. Because these leaks come from two different parts of two different roofs, they will be very hard to track and find. 

With water running across and down your shingles, it’s nearly impossible to find the origin of the leak in your roof. If you want to install a metal roof over an asphalt roof, ask your contractor about the condition of your current roof and if a metal roof-over is a good option for you. 

3. You won’t get to replace crucial roofing materials

When you get a metal roof-over, you bypass the tear-off process of getting a new roof. This will save you money, but you miss out on replacing crucial materials that are included in a full roof replacement. 

For example, one of these crucial materials is the underlayment. It’s your roof system’s last line of defense for keeping your decking dry. When you roof over your asphalt roof with a metal roof, you have to rely on the underlayment from your old roof. You also won’t get the proper kind of underlayment specifically designed for a metal roof. 

Roofing materials aren’t meant to last forever. That’s why if you’re already going to invest in a metal roof, I recommend starting from scratch with clean decking. 

To learn more about the crucial materials that are replaced when you get a new roof, read this article on the 9 materials included in your roof replacement. 

Should you get a metal or asphalt roof replacement?

Now you know you can install a metal roof over an asphalt roof. You also learned 3 warnings about getting a metal roof-over. 

Remember, while it can be done, I wouldn’t recommend it. I understand everyone has a budget, but if you’re investing in a metal roof, you should tear off your old asphalt roof. To get the best quality roof possible, you should always start from clean decking and replace all the crucial roofing materials. 

After reading this, do you still want to roof over your old asphalt roof with a metal roof? If you don’t, are you having trouble deciding between upgrading to metal or sticking with asphalt for your replacement? Luckily, we’ve developed a quiz to help you find the right roof for you. 

The team at Bill Ragan Roofing has been replacing both asphalt and metal roofs in the Nashville area since 1990. Our attention to detail and high-quality workmanship you get a new roof that lasts for decades. When you work with us, you’ll never have to worry about your roof again. 

To help you find the right roof for your replacement, take this free Which Roof is Right for You Quiz.