Metal roofing is a great option for many homeowners thanks to its durability and visual appeal. However, shingle roofs are most commonly used because they are affordable and easy to install. If you have a shingle roof, you can install metal roofing over asphalt shingles.
You might think that to transition to a metal roof you’ll need to completely rip out your asphalt shingles. But it’s possible to reduce the cost of roofing materials by installing a metal roof over existing shingles.
In this article, we’ll cover:
- Is It Possible to Install Metal Over Asphalt Shingles?
- Things to Consider Before Installing Metal Roofing Over Shingles
- Pros of Installing Metal Roofing Over Shingles
- Cons of Installing Metal Roofing Over Shingles
- How to Install Metal Roofing Over Shingles
- Cost of Installing Metal Roofing Over Shingles
- FAQ About Metal Roofing Over Shingles
Is it Possible to Install Metal Over Asphalt Shingles?
Yes, you can install a new metal roof over shingles. You don’t have to spend the time and money tearing off your existing shingle roof to install a metal roof. However, you’ll want to check with your local building department before you get to work.
In most areas, you can install metal roofing if you’re only going over one layer of shingles. But building officials might not allow you to install a new roof over two or three layers of shingles. It’s always best to check with your local building and zoning departments to make sure they approve metal-over-shingle installations.
Things to Consider Before Installing Metal Roofing Over Shingles
Here are a few things to consider before installing your metal roof:
- Building and Zoning Codes: Contact your local building and zoning departments as well as your homeowner’s association (if you have one) before you proceed with your installation. Make sure everything is legal and up to code.
- Roof Condition: Inspect your roof for rotting rafters or sheeting. Make sure your roof is in good condition before adding any metal on top.
- House Structure: Check if the current roof has structural problems like buckled trusses or sagging. You need to be sure your home is structurally sound enough to handle the added weight of a metal roof.
- Metal Protection: Add underlayment on top of the shingles to prevent the granules from corroding the metal. Make sure that adding metal on top of shingles won’t void your warranty on the product.
Pros of Installing Metal Roofing Over Shingles
Installing a metal roof over shingles offers more advantages than just saving time and money on the tear-out and installation.
Metal Roofing is Energy Efficient
A metal roof reflects and blocks heat and UV rays resulting in cooler temperatures and improved insulation inside your home. An asphalt shingle roof can reach 150 degrees on a sunny day, but under the same conditions, a cool roof, like metal, can be 50 degrees cooler.
Not only do metal roofs keep your house cooler, but they also reduce cooling costs. Having a metal roof can save you up to 25% on yearly power bills. Metal roof installation costs can be recovered from the savings in monthly cooling and heating costs.
Metal Roofing is Eco-friendly
Traditional asphalt shingles need to be replaced every 15 to 20 years. That means 7-10 million tons of old asphalt shingles are sent to landfills every year. If you are not tearing off the shingles, they are not being hauled off to the landfill.
Asphalt shingles are made of petroleum products, which means fossil fuels are used to produce them. But metal roofs are more eco-friendly because they are made of 25% to 100% recycled materials.
Metal Roofing has a Long Lifespan
If a metal roof is installed correctly over shingles, it has a lifespan of 40 to 70 years. The material’s long lifespan is the primary reason why most homeowners choose metal roofing over other types of roofs.
Metal Roofing is Durable and Weather Resistant
Metal roofing holds up in extreme weather. It can withstand wind gusts of up to 140 miles per hour and does not corrode or crack with rust-proof coatings.
Metal roofing is designed to keep the elements from damaging a home. Snow and ice will slide off the metal, and the sun warms the metal to melt the snow. Metal roofing is also fire resistant, which makes it an ideal roofing material for homes in wildfire-prone areas of the country.
Metal Roofing is Low Maintenance
Metal roofing is low maintenance compared to shingles. Asphalt shingles usually require more frequent maintenance since they can slip, crack, disintegrate and fall off. Metal is also a great material because it’s resistant to moss, mildew, algae and rot.
Cons of Installing Metal Roofing Over Shingles
There are always some drawbacks to placing a metal roof over a shingle roof.
Metal Roofing Might Not Meet Building Codes
Local building codes might not allow new roofing to be placed over the old and may require you to fully remove the old roofing system before installation. Issues with the asphalt shingles could impact your new metal roof and moisture could become trapped between the shingles and the roof. You also risk voiding your warranty on the metal roof by placing it over the existing shingles.
Metal Roofing Makes it Difficult to Repair
When you completely replace your roof, the old roof is torn off all the way down to the decking, which gives you the chance to inspect for broken boards or rot. But if you don’t tear off the shingles, you’ll have no idea if the roof decking underneath is stable.
When you bypass the removal process, you lose the opportunity to repair or replace key roofing components. Also, though metal roofing is more insulated and water resistant, any possible leak will be hard to track down and repair.
Although metal roofing is designed to withstand extreme weather, large hailstones or falling branches can put dents in metal roofing. Depending on the type of roof, you may not even be able to walk on the metal roof without creating dents. Some types of metal are stronger than others. Softer metals like aluminum and copper are more prone to this type of damage than a material like steel.
Metal Must Be Installed by a Professional
Though some homeowners know how to install their roof DIY, metal roofing installation and repair requires a unique skill set, so installation is safer in the hands of a professional roofer. Do not attempt to do it yourself since it’s a safety risk and can cause damages, which could result in voiding your warranty.
Metal is Expensive
Although installing over shingles is cheaper than ripping out the old roofing, metal roofing materials still cost more than asphalt shingle roofing. Higher-end metals run as much as 10 times the cost of asphalt shingles. The labor cost to install a metal roof is also more expensive than what you would pay for other types of roofing because of the specialized training, knowledge, tools, and equipment involved.
Metal Roofing Can Be Noisy
Even with the extra protection of an underlayment, rain and hail can be very noisy under a metal roof. If you add extra layers of solid sheathing or insulation, it will minimize the sound from outside. However, this will add to the cost of the roof, so keep that in mind.
How to Install Metal Roofing Over Shingles
The average person can’t install metal roofing over shingles since it is dangerous and could end in mistakes, so you really should hire an experienced pro. Improper roofing installations can void your warranty as well, so leave the job to the professionals!
However, it’s a good idea to know what kind of work goes into the process so you can stay informed on what to expect with a metal roofing project.
Step 1: Inspect the Plywood
Inspect the plywood decking under the existing shingle roof to check that it’s still in good condition. It’s important to resolve any rotting and corrosion before installing your metal roof. If the plywood is in good shape, then it’s OK to continue the metal roofing installation.
Step 2: Inspect Shingles
You should look for moss and algae growing on the shingles since they will soak up rainwater like a sponge, trapping moisture, which can seep into the sheathing below the shingles and cause serious damage to the roof. You also should look for curled or buckling shingles, as well as damaged, missing, or old shingles, and replace them as needed.
Step 3: Install the Underlayment
Installing new underlayment will keep the asphalt shingle granules from running up against the new metal roof, which could cause damage over time. Underlayment comes in a felt-type material and synthetic material. Your goal with the underlayment is to make sure everything is as straight and as square as possible.
Also, keep in mind that flashing will need to be installed for dormers, chimneys, or any possible seam where you are especially concerned about water. You are aiming for a very square, symmetrical look without the risk of water damage later.
Step 4: Add Insulation
Adding E-foil insulation to the top of the underlayment provides a protective surface between the asphalt and the metal. This layer also increases energy efficiency by reflecting heat away from the roof.
Step 5: Install Metal Roof Panels
Directly On Top of Underlayment Method:
- Use a measuring tape to determine the exact amount of material you need for the total roof surface area. You will need to measure valleys, dormers, and chimneys. You will also need to think in terms of each side of your roof.
- Start putting the panels into place and fasten them with screws and a cordless drill. Start straight and keep the edges straight. Keep everything as square and symmetrical as possible. Be careful not to scratch the colored surfaces of the metal, or it might rust later. E-foil insulation is best paired with corrugated metal, which creates a natural venting process.
- Install rubber or foam closure strips that match the shape of the metal when working with any overlaps. The goal is to prevent any water damage later.
- Attach the ridge cap, which needs closures to prevent leaking.
Wooden Purlin Method:
Wooden purlins are structures placed over the shingles, so you don’t lay the metal roofing directly over the shingles and underlayment.
- Run a measuring tape from end to end along the rafters of the roof to determine how many purlins you will need. Measure the width and height of the roof. Remember to record the measurements on a piece of paper, so you don’t forget.
- Begin laying the first purlin at the ridge of the roof, beginning at either corner. Fasten with 16d nails into each vertical rafter.
- Place purlins like this until the first row is complete. If the last purlin is too long, then cut it to size with tin snips.
- Install the second row of purlins just like the first. Continue down the roof until it is covered with purlins.
- Start putting the panels into place and fasten them with screws and a cordless drill. Start straight and keep the edges straight. Keep everything square and symmetrical.
- Install rubber or foam closure strips that match the shape of the metal.
- Attach the ridge cap.
Cost of Installing Metal Roofing Over Shingles
FAQ About Metal Roofing Over Shingles
All metal roofs need an underlayment. It’s the layer beneath the roofing system that serves as a weather-resistance barrier, providing greater moisture protection. It also protects the metal roof from shingles expanding and contracting, which can cause damage underneath the metal roof over time.
Choosing the right underlayment is as important as choosing the right roofing material. The most common materials used for roof underlayment are felt self-adhering membranes and synthetic sheets.
Metal roofing does not cause issues with internet connections. Not only will a metal roof not block Wi-Fi signals, it also won’t cause problems with cellphone reception.
You cannot put a metal roof over three layers of shingles in most cases. A majority of local building departments will allow one layer of shingles but not three.
When to Hire a Roofing Pro
Why spend your free time studying roofs when you can hire an experienced and reliable roofing pro instead? Roof installation is hot, back-breaking work and not meant for someone who is not an experienced roofer.
If you want to install a new metal roof over your shingles, find an experienced roofing pro near you.