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Why You Shouldn’t Install Metal Roofs over Shingle Roofs (5 Reasons)

March 3, 2023 | 3 min. read

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Metal roofs are expensive. If homeowners want the cool vibes of a metal roof on a budget,  they’ll try to save money where they can.

Some homeowners install a metal roof over their current asphalt roof to save money. While it may be possible to do this, it’s not recommended. There will be problems that come with it. 

For over a decade, Rescue My Roof has educated homeowners like you – helping them easily navigate the roof-buying process. 

This article will help you understand the problems associated with putting a metal roof over a shingle roof. Ultimately, you’ll know how to move forward without causing damage to your home. 

5 Problems with Installing a Metal Roof Over an Old Shingle Roof

Installing a metal roof over an existing roof has its fair share of problems. 

Here are the top five issues you could run into. 

1. No Chance to Replace Bad Roof Decking

An asphalt roof torn down to its rotten decking covered with black water damage.

Roof decking is the wooden board that is the foundation of your roof. 

When getting a replacement, your roof is torn down to its decking. This allows your contractor to inspect the decking for broken boards or signs of rotting. 

When you don’t tear off the existing roof, there’s no opportunity to inspect your roof’s decking. 

This means a few things: you don’t know if the decking’s integrity can handle your new roof, and you could need early repairs.

There is a chance your decking is fine. But most roof replacements require a partial decking replacement; some need it replaced entirely. 

To avoid issues with decking and roof stability, tear off your existing roof before installing a metal roof. 

2. The Added Weight of a Metal Roof

Roofer worker in protective uniform wear and gloves, using air or pneumatic nail gun and installing asphalt shingle on top of the new roof,Concept of residential building under construction.

When installing a metal shell over a shingle roof, you may have broken decking boards or rotting you can’t see. 

A metal roof will add some weight to your roof that your decking must hold.

If your decking’s integrity is compromised, the added weight of a metal roof can cause structural damage to your roof and home. 

This may not happen immediately unless the decking’s damage is severe. However, the weight will become a problem if the decking continues to rot. 

If you hire a reputable roofing contractor, they won’t recommend installing a metal roof over the top for this reason alone. 

3. Essential Roofing Components Can’t Be Replaced

A roof replacement is a chance to replace old roofing materials and components (decking, flashing, gutters, etc.) that have reached the end of their life. You don’t get to do this when you bypass the tear-off process.

Skipping demolition may save you money upfront, but you miss out on replacing essential materials that shouldn’t be on your roof anymore. Ultimately, you’ll spend the money you saved and then some on future repairs. 

Additionally, you would get the proper underlayments designed for a metal roof. These components give you better warranties and make your roof effective. 

If you want a roof that will indeed keep your home and family safe, you’ll follow the manufacturer’s installation and roofing accessories guidance. 

4. Future Leaks Are Hard to Track and Repair

If you see water damage from a leak, chances are the leak isn’t right above it. Leaks can be difficult for even professionals to track. It’s even harder to do this when you install a metal roof over shingles. 

If water gets under the metal panels, it’ll go down your old asphalt roof and leak inside your home. It’s challenging to repair as the leak could come from two different parts of two different roofs. 

If you find a leak, a professional must go through the metal roof to repair it. 

If you are considering laying a metal roof over shingles, ask a professional to inspect the state of your current roof. 

5. Roof Issues Won’t Go Away

The cost of repairing a roof leak: interior damage

Putting a new roof over the old is like putting a bandaid on a wound that requires stitches. Issues with your old shingle roof don’t magically vanish when you install a metal roof. 

If your asphalt roof is covered up without taking care of a problem, it will still be there when water gets through your metal roof. You’ll spend more money to fix a problem that isn’t guaranteed to disappear permanently. 

This moisture can also rot your shingles over time. No matter the problem with your old roof, installing a new one over it doesn’t ensure the same problems will occur again. 

Installing A Metal Roof the Right Way

Avoid future repairs and commit to tearing off your current roof before installing a metal one. 

You will avoid issues with the decking, added weight, and leaks. Additionally, it may save you money in the long run. 

You can learn more about metal roofs with “4 Things to Look For in A Metal Roof” and “The Top 3 Strongest Roofing Materials.” 

Additionally, you can download our Buyer’s Guide to help you purchase the roof of your dreams.
While we don’t install metal roofs, if you want an asphalt roof replacement, contact Rescue My Roof to get a free estimate.