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Metal Roof Over Shingles – Pros and Cons

Published on: November 15, 2021

Re-roofing a home or building is a large project, which is why some people prefer to place new roofing materials over the old ones to save time and expense of removing the old shingles. But when you’re installing a metal roof that is designed to last 50-70 years, should you leave the old asphalt shingles in place?

While it’s possible to place a metal roof over shingles, that doesn’t necessarily mean that you should do it. The status of your asphalt shingles and your reasoning for placing the metal roof over them will be factors in whether this is a good idea for your property or not.

To guide you in deciding whether to place your metal roof over your existing shingles or to take the time to remove the old building materials, we’ll outline the pros and cons of each and some key considerations that will contribute to deciding how to handle your re-roofing project.

Pros and Cons of Installing a Metal Roof Over Shingles

Roofing installation can take a few days depending on the size of your home or building. So should you speed up that process by placing a metal roof over your existing shingles? Here are the pros and cons of each method.

Pros of Installing Metal Roof Without Shingle Removal

  • Cost savings from not having to remove existing shingles, resulting in less labor expenses
  • Greater insulation for your home or building thanks to additional roofing layers
  • Shorter project timeline due to not needing to allow time to remove the existing roofing materials
  • Eco-friendlier because you won’t need to send the asphalt shingles to a landfill

Cons of Placing Metal Roof Over Asphalt Shingles

  • Some building codes do not allow for placing new roofing over the old roofing materials
  • Issues with the asphalt shingles could impact your new metal roof
  • Moisture can become trapped between the asphalt shingles and the metal roof
  • You might void your warranty on the metal roof by placing it over the existing shingles

Allow the Professionals to Do It

So while you might save some time and money on placing your new roof over the old one, you could encounter extremely large issues that would result in you spending more time and money on your roof than you would have if you’d removed the original roofing materials at the start of the project.

Deciding Factors for Placing Metal Roof Over Existing Materials

Based on the cons listed above for adding a metal roof without removing the old one, there are 4 deciding factors for whether you should place your metal roof over the existing one.

1. Review Building Codes in Your Area

The fines for building code violations can be enormous. In some areas, you don’t have the option to place new roofing materials over the old ones, regardless of the roofing material you select. Before deciding the best course of action for your project, check your local building codes for more information on placing new materials over the old ones.

2. State of Your Existing Roof

Old roofs with problems can cause issues with your new roof if you leave the materials in place. Actually, you can make your roof problems worse by placing materials over them. One problem you might face is the roof becoming too heavy for your structure. If that happens, you might experience buckling or sagging, which could cause severe structural damage.

To determine whether you can place new roofing materials over the existing ones, look for rotted wood sheeting or rafters. And fix all leaks in your roof before adding the materials over your existing roof. Fixing the existing shingle roof can be cost-prohibitive, leading to simply removing the original roof before installing the metal roof.

3. Check Whether Moisture Can Get Trapped Between Roofing Materials

A big reason people install metal roofs is because they are mildew and rot-resistant. But if moisture can get between your metal roof and your existing asphalt shingles, that great benefit is non-existent. Moisture between your roofing materials will still lead to mold, mildew and rot. 

Ask an expert about ridge vents and furring strips to prevent moisture from getting under your metal roof. Generally, your roofing underlayment is what prevents moisture from being a problem with your home and its materials. But the integrity of that underlayment could be jeopardized based on you placing the new materials over the old ones.

4. Check Your Roofing Warranty Language

Metal roof manufacturers might require that you install it directly onto your home without old materials underneath. Failing to follow the installation guidelines could lead to voiding your roofing material warranty. Or, your roofing contractor might not provide a warranty on the installation work if you install your roof without removing the old materials.

Metal Roof Vs Shingles

One of the big reasons some people look to place their new metal roof over existing asphalt shingles is because of the cost of metal roofs. So if you shouldn’t place your metal roof over existing shingles, is the price of a metal roof really worth it? 

Here’s a look at metal roofs vs shingles to provide insight into the cost and benefit you can experience from selecting this roofing type.

Durability

Metal roofs are far more durable than shingle roofs. They last 40-70 years on average and have longer warranties of about 30-40 years. They stand up to extreme weather, hail and falling objects well. The materials used in your metal roof will impact its durability though. For example, you might want a steel roof instead of copper because steel offers better protection for your home.

Shingles have weaknesses and can allow water to pool during large rain storms or extended wet periods. In Washington, we see a great deal of rain, making metal roofs a good idea.

Cost

The upfront cost of a metal roof is far more than that of asphalt shingles. However, the total cost of the roof over the decades that it protects your home is less for a metal roof. If you can spend the money upfront, the lifelong cost of a metal roof will be worth it.

Eco-friendly

Metal roofs can be made from recycled materials. And when you’re done with your metal roof, those materials can be recycled again to prevent them from going to a landfill. Asphalt roofs go to the landfill once you are done with them.

Installation and Repair

Installing and repairing asphalt shingle roofs is far easier than metal roofs. Metal roofs require special tools and expertise that not all roofers have. Shingle roofs generally take a day or two for installation depending on the size of your roof and the size of your roofing team. Is a metal roof right for you? It all depends on your home and your needs. Before determining whether to place your new roof over your existing materials, you should meet with an expert to review your deciding factors. Schedule a free consultation and estimate with the 2FL team to learn more about re-roofing your home.

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  1. […] the pros and cons of metal roofs and shingles to see how the options stack up. What is best for one person and their home might be different than […]

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