Common Metal Roof Over Shingles Problems and Solutions

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By George Taylor

Updated: Jan 25, 2024

8 min read

Metal Roof Over Shingles Problems

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    Acquiring a new roof can be very costly. You opt to put a metal roof over your pre-existing shingles roof to avoid the cost of replacing them with a new roof. Unfortunately, this option does not make sense and some common problems arise.

    Installing a metal roof over shingles may seem like a simple job but it isn’t so.Every professional expert knows that installing metal roofs takes work and experience. And if you don’t have it then, Not having a metal roof over your existing shingles roof will be a good option.

    Also Read: How to Install Metal Roofing Over Shingles?

    Inadequate Roof Inspection

    The difficulty is that if you install a metal roof over the shingles roof, there is no way to inspect your roof deck. Measuring the integrity and strength of the deck structure that can hold your new roof is almost impossible. Sadly, you won’t know about the problem until it’s too late. Now, it is possible that your roof terrace will not have any problems. However, most roof replacements require a few replacement of shingles, and some even require the entire roof to be replaced.

    Improper Installation Techniques

    Installing a new heavy metal roof over your existing shingles roof will require the shingles boards to withhold the weight involved. And if they can’t install it properly, then the shingles boards can rot and break down. The weight of a metal roof can even lead to damage to your whole roof. So, professional expert guidance should be taken to properly install the metal roof over the shingles roofing.

    Moisture Trapped Between Layers

    The problems associated with an old shingle roof will not disappear by covering it with a metal roof. If your asphalt shingle roof is hastily covered, moisture will be there when you opt for a metal roof over it. That means you’ll spend even more money fixing a problem that won’t go away permanently.

    Moisture Trapped Between Shingles roofs

    Moisture gets trapped in the deck space, creating dampness and fungus to your roofing. Installation of a metal roof over your pre-existing shingles doesn’t mean these complications won’t reappear.

    Structural Concerns and Weight Issues

    The main components of the roof cannot be replaced. Roof replacement is a time to replace old roofing materials and parts that have reached the end of their life. While installing your metal over shingles roofs, you are still in this choice. It might give you a cost saving, the problem is that you cannot replace important components that are no longer required.

    The underlayment is installed directly on your patio and is the last line of defense for the roofing. When installing a metal roof over a shingle, you must rely on the foundation of the old roofing system. Not only that, but you won’t get a proper base that is specifically designed for metal roofing. Roofing materials are not meant to last; thus, tearing down before installing a new roof would be a better choice.

    Additional Weight on the Roof Structure

    The deck boards can crack, as installing a metal roof over shingles adds weight to your existing roof structure. The cohesive structure is compromised, leading to permanent structural damage to your roof and, in turn, your whole home. The roof seems to crumble from the weight of the metal roof over the shingles.

    Inadequate Ventilation

    If you install a metal roof over shingles, it can block airflow in the roof space. This can lead to dampness and fungi growth.

    Installing a metal roof over shingles traps water vapor and moisture between the two layers of roofing material. This excess moisture quickly causes mold to grow, which eats away at the roofing material and can even end up in your home.

    In addition, people with asthma and respiratory allergies may experience greater problems and adverse health effects.

    Compatibility and Expansion/Contraction Issues

    Installing metal roofing over shingles can cause compatibility issues. The temperature alterations can lead to expansion and contraction while installing a metal roof over your shingles roof. Mixing the metal roof over the shingles roof can give you unwanted leakages due to the contraction and expansion of material used in making metal and shingles, respectively.

    Also Read: The Best Roof Covering Ideas To Elevate Your Home’s Look

    The fitting techniques and the substance used in these two types of roofs may differ, creating consistency and circulation issues like gluing material with each other and giving small spaces to your roof.

    Before taking a final call on whether to go with the idea of installing a metal roof over your existing shingles roof, please ensure the material and fitting techniques are compatible.

    Long-Term Maintenance and Warranty Concerns

    Ceiling installation must be installed according to the manufacturer’s standards. If you put a metal roof over an asphalt roof, you automatically void any asphalt roof warranty. Also, the metal roof in this situation would not have a material or labor warranty because it was improperly installed. This means as soon as there are potential problems, you won’t be able to carry out any repair work under the warranty as you have no protection. All repairs must be paid for completely out of pocket.


    Putting a metal roof on top of the shingle roof is feasible, but you need to ensure that the plywood under the shingle roof is in good condition to support the new metal roof. If you choose to do this, you can save a lot of money, but it can also cost you more potential problems. To save your cost in the short term, you would incur a long term cost of repair and maintenance on the installation of metal roof over shingles.


    Is It Better to Remove Shingles Before Installing a Metal Roof?

    Yes, removing the shingles before installing a metal roof is better to avoid any long-term maintenance and repair issues.

    Pros and Cons of Putting Metal Roof Over Shingles?

    The most significant advantage of putting the metal roof over shingles is that it saves money on demolishing the existing roof. In contrast, adding weight to your existing roof structure is the biggest downside.

    What is the Biggest Problem With Metal Roofs?

    Leaking and corrosion are the biggest problems with metal roofs.

    Is It Okay to Put a Metal Roof Over Shingles?

    It would be good for you if you could tear apart your shingles roof before installing the metal roof, but if you want to save the cost, then it is good to go with the installation of metal roof over shingles.

    Can you go over existing shingles with a metal roof?

    Yes, you can go over existing shingles with a metal roof.

    What is the Best Way to Put a Metal Roof Over a Shingle Roof?

    If you handle it correctly, you must remove the shingles from the area where the metal part will go. Then, the metal pieces continue, and the flashing continues. Finally, the shingles go over the flashing and metal edge to complete the transition.

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