Everyone at some point has heard of the saying “out with the old, in with the new.” But when it comes to roofing, a new roofing material does not necessarily mean you have to get rid of the old one.
A home that removed asphalt shingles and installed a standing seam metal roof
If you’re getting ready to make a big roofing change from asphalt shingles to metal, you’ll have to first make a decision on what to do with your old shingle roof. One option is that your old shingles can be removed prior to the new metal roof being installed, but that is not your only choice. It may come as a surprise that a metal roof can actually be installed over your existing shingle roof.
But just because something can be done, does that mean you should do it?
At Western States Metal Roofing, we have over two decades of experience with customers upgrading from asphalt shingles to a metal roof that are faced with this exact decision. We believe that this choice should be made on a case by case basis. It depends on different factors and every roof is going to be different from the next.
In this article, you’ll learn more about re-roofing (installing your new roof over an existing roof). We will also go over 4 factors to consider when deciding if you should remove your asphalt shingle roof before you install a metal roof.
Installing Metal Roof Over Shingles Pros And Cons
There are many advantages to putting your new roof over the old roof, which is a process that can be known as either overlaying, or re-roofing.
Pros Of Putting A Metal Roof Over Shingles
- You’ll save on labor costs. Not removing the asphalt roof first results in less work for the contractor.
- Added insulation protection to your home by having extra roofing layers.
- Faster installation as less labor is required.
- Eco-friendly because the old asphalt shingles will not have to be thrown away.
Metal is an easy material to use when re-roofing because it’s a lightweight material. It weighs less than one pound per square foot. A new metal roof won’t put a lot of extra stress on your home, even with your old asphalt shingle roof also still attached underneath.
Cons Of Putting A Metal Roof Over Shingles
- It Is Restricted By Some Building Code
- Problems With Shingles May Affect The New Roofing
- Moisture Can Become Trapped
- May Void Your Warranty
We go into detail on each of these issues and the questions you should consider before deciding if you should put a metal roof over your shingle roof.
1. Does The Building Code Allow For A Metal Roof To Be Placed Over Shingles?
The choice is easy when there isn’t a decision to be made. Local building code can make your decision simple if it specifies that the existing shingles have to be removed first.
It’s common to find building codes that will allow for two layers of roofing on a structure, but that is not always the case. Check your local building codes to see what is allowed in your area. Not complying with building codes can result in expensive fines.
2. Are There Problems With Your Previous Roof?
If there are problems with your old roof, putting a new roof on is not going to fix them. In fact, it will eventually make them worse.
If your previous roof weighs more than the structure of your home can adequately handle, adding the additional weight of the metal roof will cause a bigger problem. Some warning signs of problems from the weight of your roof may include buckling trusses or sagging roof decking. Prior to installing a metal roof over an existing shingle roof fix any rotten wood sheeting or rafters.
If your asphalt shingle roof has leaks, those problems need to be addressed. Parts of the roofing system may have water damage, and these issues would have to be repaired or replaced. You may have already noticed water damage issues that led you to determine you need a new roof in the first place. Ignoring these issues will lead to a shorter lifespan for your new roof and more expenses in the future.
3. Can Moisture Get Trapped Between The Metal And Asphalt Shingles?
One of the benefits of a metal roof is that it is resistant to rotting and mildew. However, this benefit is cancelled out if moisture is able to get in between the new metal roofing panels and the old asphalt shingle roof.
Moisture between these surfaces can result in mold and rotting which will ultimately lead to costly repairs.
Here are two ways to eliminate trapped water vapor:
- Ridge vents are designed to create constant air flow along the horizontal ridge of your house. They create a space for airflow that allows moisture to escape.
- Furring strips will raise the metal roofing and allow for ventilating air pockets between the metal and shingles.
Every roof is different and must be analyzed by the roofing contractor to determine what’s best for your specific roof. However, all metal roofs should have roofing underlayment regardless of whether it’s a new installation or being installed on top of an existing shingle roof. Roofing underlayment creates an added layer of protection from moisture.
To learn more about how roofing underlayment helps block moisture, we suggest reading:
Does Metal Roofing Need Underlayment? A Guide For Homeowners
To learn more about how ridge vents will increase airflow and lower energy costs, we suggest reading:
Ridge Vents For Metal Roofs. Everything You Need To Know
4. Will The Warranty On The Metal Roof Be Void If Installed Over Shingles?
The specifications of your metal roof warranty will vary depending on the manufacturer. You, or your installer, must check the metal roof warranty to make sure that you aren’t breaching the warranty terms by installing it over asphalt shingles. Doing so will leave you without any coverage on your brand new roof.
Is It OK To Put A Metal Roof Over Shingles?
Depending on the situation, it may be fine to put a metal roof on top of shingles. It’s important to take the specific factors of your roof replacement into consideration when deciding what to do about removing your old roof or not.
You should remove your old asphalt shingle roof before installing a metal roof when:
- There are signs of structural issues from the weight of your roof.
- There is leaking or other damage caused by your current roof.
- Your metal roof warranty will be void by installing over asphalt shingles.
- You have to in order to comply with local building codes.
You may decide to install a metal roofing material over old asphalt shingle roof when:
- It’s in compliance with your local building code.
- You are using roofing underlayment and vented ridge cap to prevent moisture buildup.
- You are looking to save money in the short term by saving on labor costs.
- You will still be eligible for warranty coverage.
No matter which way you decide to go, avoiding errors during installation is crucial to the longevity of your metal roof. The installation of your new metal roof requires a different set of skills than installing a shingle roof. It’s important to hire a qualified metal roofing contractor to do your installation.
Haven't decided on a color or style for your new metal roof? Download our free guide to choosing the right metal roof color!
Corrugated metal roof or standing seam? If you're not sure which type of metal roof you're interested in, watch our video below to learn the differences between these roofing systems.
