When it comes to replacing your roof, you may be considering a transition to metal instead of wood or asphalt shingles. After all, there are many benefits to metal roofs.
The biggest question people have about metal roofs is if you can install this roofing over the top of asphalt shingles. The short answer is yes. In most cases, it is possible to place metal roofs directly over shingles without removing the existing roof. However, there are some situations where it wouldn't be possible.
Keep reading to learn all about installing a metal roof over shingles and the dos and don'ts of this roofing method, including metal roof over shingles problems you may experience during or after installation.
Table of Contents
- Can I Install Metal Roof Over Shingles?
- Factors that Must Be Considered
- Metal Roof Over Shingles Pros and Cons
- Potential Issues After Installing
- How to Install Metal Over Shingles
Can I Install Metal Roof Over Shingles?
Yes, it is absolutely possible to install a metal roof over shingles - overlay - instead of having to tear the shingles off. Having to remove all of the shingles from your roof can be costly and take a lot of extra time and labor.
Shingles are heavy, with some weighing up to 4 pounds a square foot. But metal weighs less than one pound per square foot, so it doesn't add an excessive amount of weight. Roofs with too much weight can sustain structural damage. The lightweight of metal allows it to go over the top of shingles to save you money, time, while not affecting the max weight capacity of your roof.
Keeping your existing layer of shingles and placing metal roofing on top also provides an extra layer of insulation, which reduces noise, blocks heat from coming into the house, and can help reduce your energy bills.
Factors that Must Be Considered
Comply with local building codes
It's a good idea to verify that installing metal over shingles is in accordance with the local building code by making calls to your local zoning and building departments. In rare cases, there may be ordinances that prevent this method or require special handling during install.
A standard regulation will be on the number of shingle layers. One layer is typically okay, but there are some states with restrictions on two or more layers. This rule is due to the weight limit of house trusses, which varies by home. When there are multiple layers of shingles, the trusses can have too much weight, putting the homeowners at risk of the tresses falling, damaging the roof.
Ensure the condition of the existing shingle roof
The condition of your existing roof is also crucial to consider. Covering the area with metal sheets without repairing the damage can lead to more significant problems. The first thing to do is check the condition of the existing plywood, ensuring there are no soft spots that can affect the hold of the screws which mount the metal in place. Also inspect your roof for signs of breakage or shingle damage caused by leaks.
Eliminate structural problems
Another issue to consider is if your roof is experiencing structural problems, such as sagging decking or truss buckling. Although metal panels do not weigh a lot, shingles' weight can cause stress to an already weakened roof structure. It's best to address any structural issues before installing a new metal roof over shingles.
Add underlayer or not
Whether to install the underlayer is also an issue. Shingles have a rough texture, which can rub against metal and cause it to lose its protective coating. As the metal wears down, it can be more susceptible to corrosion, thinning, and scratches, reducing the roof's lifespan.
An underlayment placed between the layer of shingles and metal can prevent these issues. Which type you use will depend on the type of metal you're installing.
The final factor to consider is the shape of your roof life. Flat roofs with zero pitch are not suitable for metal roofs because there's no way for the water to drain off when it rains. Standing water can lead to rusting and compromised structural integrity. For you to install metal over shingles, flat roofs must have a low pitch at minimum. You can also use metal for steep-pitched roofs.
Metal Roof Over Shingles Pros and Cons
There are many benefits and disadvantages of hanging a metal roof over shingles rather than removing the shingles before adding your metal panels. It's important to consider all of these factors when you decide whether to install it or not.
- Save Money
Tearing off the old shingles can be expensive. The costs will include labor, time, and material disposal. When you add a metal roof over the top of existing shingles, you're only paying for the installation and new materials, which are drastically lower than the price of shingles.
- Longer Lifespan
Compared to the shingle roof, once you install a metal roof, it will last nearly a lifetime, with a longevity of 40 to 70 years of use. Shingled roofs have a shorter lifespan of 12 to 20 years, which means it’ll need replacing several times within the same timeframe.
- Nearly Indestructible
Regardless of weather conditions, a metal roof should not fail or damage. They can withstand ice storms, pounding hail, intense summer heats, and gale-force winds up to 140 mph. These roofs will also not crack or corrode due to rust-proof coatings. They're even fireproof and impervious to insect damage like termites and carpenter bees.
Asphalt shingles contain petroleum, which can harm the environment when ripped off the roof and put into landfills. When you leave the shingles on your roof and cover it with metal, you're helping protect our planet. Metal roofs are more environmentally friendly, as they're often recycled materials and are fully recyclable after you've taken them off the roof.
Many homeowners also turn to metal roofs to use other green-friendly solutions like rainwater collectors or solar panels. Adding these features to an asphalt shingle roof can be more expensive and less effective.
- Energy saving
Metal has reflective properties that block solar radiant heat, so your house is easier to cool and heat. Some types have unique reflective pigments that minimize heat gain, so less heat enters your home. Asphalt shingles absorb this heat, increasing the costs you pay for cooling.
- Noise reduction
Some people enjoy the sounds of a tin roof, especially when it's raining. But if there's nothing to reduce the noise, it can get pretty loud. There are ways to ensure metal roofs don’t make any more noise than other roofing types.
Adding a roof deck, insulation, and underlayment will help dampen any noise. Without all of these elements, a metal roof will be close to deafening. Leaving shingles under metal is another easy and effective additional noise barrier.
One of the biggest concerns of choosing a metal roof is the cost. The cheapest way to install a new metal roof is to put it over existing shingles. Having to pay for a complete tear-off of the old shingles is extremely costly.
The upfront costs of metal is also expensive compared to the cost of shingles. One square - 100 square feet - of metal can range from $120 to $900, although higher-end metal roofing can cost more than ten times the amount of asphalt shingles.
The cost of labor for the installation of metal roofs is also higher. Metal roof installation requires specialized equipment, tools, training, and knowledge, making the final cost higher than you would pay for an asphalt roof.
If the roofers have to tear off the existing shingles before adding the metal panels, you'll pay an even higher price. Having to repair any damages before installing your metal roof can add up the final cost even more.
However, in the long run, your investment in a metal roof pays off, as you'll only pay this fee once and probably won't have to do anything else to your roof for decades. When you have an asphalt roof, you'd have to replace the materials multiple times within the same time frame, which adds up to cost more than a metal roof.
Potential Issues After Installing
When done properly, installing a metal roof over shingles will not have any problems. But there are some potential issues that you may experience.
One problem that occurs from putting metal over shingles is moisture buildup under the metal. If you notice your metal roof dripping water even though there hasn't been any rain, you're likely dealing with condensation. This issue can occur when there's space between metal and the foundation and there’s no vapor barrier present.
- Mold and rot
When moisture starts to build up between a metal roof and shingles, you can end up with rot, mildew, or mold growth. With continued exposure, rotting can cause the wood structure to weaken. You may end up having to tear off the metal roof, the old shingles, and replace crucial parts of the home's structure.
- Hides existing problems
Another issue some homeowners experience from installing a metal roof over shingles is that you may miss existing problems with your existing shingle roof. When you don't tear off the shingles and inspect the structure of your roof, you might not notice signs of leaks, rots, mold, warps, or other evidence of damage. Without being addressed, these issues can get worse, leading to damage of your new metal roof.
- Weak hold
When you mount metal over shingles, you have to use fasteners that are long and sturdy enough to go through the metal, underlayment, existing shingle layers, and down into the rafters. An issue that commonly occurs when adding metal over shingles is improper placement of the fasteners.
It can be hard to locate the proper place to add the screws if you can't view the wood. If your screws don't go deep enough, either due to being too short or because you missed the mark, the metal won't be as secure on your roof. Severe storms or strong winds may cause damage to the metal.
How to Install Metal Over Shingles
Installing a metal roof is a big job. It can be a tricky process due to the materials and tools needed. If you have experience working with roofing or other difficult home improvement projects, you can DIY installing a metal roof over shingles. Your experience level may affect which type of metal roofing you install.
Installing an overlay - placing metal over shingles - requires placing an underlayment over the shingles to provide a safety barrier to reduce condensation and prevent damage to the metal. On flat, even roofs, you can place the metal roofing directly on top of the underlayment barrier.
Another option for placing metal roofs over shingles is to place down purlins - long straight boards - over top of the underlayment and then screw the metal to these boards. This method is preferred for installing metal siding or for standing seam panels.
Before you lay down your metal, you have to install edging - metal eave flashing - along the outline of the roof. Then you lay down each metal piece, using the appropriate method for your type of roofing.
With standing seam panels, which are long straight pieces, they run vertically from the eave to the ridge on the roofline. Metal shingles lay horizontally in stacked rows.
You also have to go through the time consuming process of applying silicone sealant along each panel after mounting it to the roof. Then, you have to install any roof vents. A roof vent installation kit includes everything you'd need for this job. Then you have to complete the job by installing flashing over all joints.
As you can see, there are multiple steps to installing a metal roof. It's best to leave this job to the professionals if you're not an expert. While you are paying more, most roofing companies provide guarantees on their product. If anything goes wrong, you're protected for free. This will save you a lot of trouble later.
We always like to conclude our guides by answering some frequently asked questions that we may not have already covered in the previous sections. Here are some common questions customers have about installing a metal roof over existing shingles.
Q: What's the Best Method to Install a Metal Roof over Shingles?
A: The method you use to install a metal roof over shingles will depend on your roofline's shape. The quickest way is to place an approved underlayment directly over the shingles and then put down your metal. However, if your roof isn't completely flat, you may do better using purlins or decking to create a flat surface.
Q: Will I Need to Use Underlayment For a Metal Roof?
A: Underlayment is a necessity for all types of roofing, not just metal. While shingles will work as a second layer to prevent moisture and reduce noise, the abrasions from the shingles expanding and contrasting can cause damage to the metal. An underlayment such as felt prevents damage to the metal roofing.
Q: Can a Metal Roof Go Over Three Layers of Shingles?
A: If your roof has three or more layers of existing shingles, you will not be able to add a metal roof on top. Most code enforcement offices have restrictions that limit roof layers to one or sometimes two. For this reason, you would have to remove layers of your shingles to meet your local guidelines requirements.