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Problems With Metal Roof Over Shingles

By May 26, 20212 Comments
Metal roof

You want to change the look of your roof as there are new styles and new trends. But, where do you start? Find the type of roof that you like and also one that is approved for where you live. Do you have shingles on your roof and wondering if you can put a new roof over it?

Well, there are problems with a metal roof over shingles or any kind of roof. One of them is putting a roof over shingles means that down the road you will have issues with the shingles and need to replace them. That will be difficult with a metal roof on top. You also don’t know if there is rot or damage underneath the second layer. In addition, there is missed damage underneath the roof, water can become trapped, may be out of building code compliant to name a few.

Let’s take a look at why you need to know about problems with metal roofs over shingles, the problems that come with it, after the new metal roof is added, and when to call a professional.

Why You Need to Know About Metal Roof Over Shingles Problems

Installing a metal roof over shingles sounds like a great idea, less messy and easier to add to the roof. However, is it really? Yes, you will save money but you will be covering up dangers and that could lead to more money down the road. Also, shingles have a life span of 15-20 years, and covering them up doesn’t mean they will last longer. All good things do come to an end.

Problem 1: Missed Damage & Shortened Roof Lifespan

When choosing to install a metal roof over shingles, you are going to miss damages under the roof. For example, you won’t know that there is wood rotting. Also, do you know for sure that roof sheathing was replaced? This is the layer of wood that attaches to the trusses and joists on the roof and keeps the water out of the home. You want to assume it is there but once you have a water leak, you will know that it may be rotting.

In addition, your new metal roof will have a shortened lifespan compared to if it was just installed on top of the roof decking. So while you save money in the short term by not paying for a removal of shingles, in the longterm you may end up paying more.

Problem 2: Trapped Water Vapor and Moisture

Another problem with metal roofs over shingles is water vapor and moisture can get trapped between the two layers of roofs, thus another reason why the shingles should be removed. Unfortunately, it can result in new mold and rot if you don’t remove it. Also removing it will allow you to look at the trusses and the roof from inside the attic to see if there are any issues.

Ridge vents

How to Avoid This Issue

Install Ridge Vents

Ridge vents run along the ridge of the roof and allow the warm air to escape at the top of the attic. Thus helping keep the attic cool. They work well with the soffit ventilation which is beneath the eaves and brings in the cooler air. It is essential that the vents are open and not full of debris or insulation for them to be effective.

Problem 3: Not in Compliance With the Building Code

Building codes according to the state in which the home is located can dictate what you can do with your roof. You can find building codes here. Some states might say you can put a layer on top of the existing roof, while others say you cannot. If you go against the codes you can pay very hefty fines and have to replace your roof entirely.

Problem 4: Problems With the Previous Roof

If you have problems with the previous roof, they won’t go away by just adding another roof on top. If you add the heavyweight of a metal roof and there are structural, foundation, or rotten wood issues, these won’t go away. You will need to check for these before adding the new roof. For example, you don’t want to add a new roof to this example below unless the shingles are fixed

Damaged roof

Problem 5: Warranty May Be Voided

Check the warranty for your metal roof and see if it becomes void if it is installed over asphalt shingles or any type of shingles. Knowing what the warrant says is important to make sure you are not spending money on something that will not work.

Problem 6: Chalking and Fading

Chalking and fading of the paint can happen because of the UV rays on a house. In Georgia, we are in the south so the sunlight is very strong. However, no matter where you live, the roof can chalk and fade. There is no specific amount of time that it takes for this to occur, but many companies do offer a warranty for it.

Counter flashing
Counter flashing example of installer error. The flashing should be up higher on the wall.

Problem 7: Leaky Roof Due to Installer Error

Sometimes problems don’t come from the materials themselves but from the installer. Unfortunately, we can order and get a great roof to put on the home but if the installer makes errors then that is an issue. One of those issues can be forgetting to (or not wanting to) install counter flashing on the roof next to the chimney properly to keep it from leaking.

Other issues that can occur are seams that fail, fasteners that fail, and not following manufacturer directions to name a few. It is a good idea to have the roof inspected to make sure it was installed correctly.

Here is a great video about putting a metal roof over a shingle roof:

After Adding the Metal Roof

After adding the metal roof, there are a few things to check for:

If you have a chimney, make sure you have roof crickets installed. This is a sloped backing that is built onto the chimney to allow water to run down the roof.

Check the gutters and downspouts and make sure they are clear. If they back up, water will leak into the house.

Look over the roof inspection checklist to see if there are any other issues.

When to Call a Professional

It is always recommended that if you want a new roof installed to call a professional. They usually will know what the requirements are for the installation if your home is sturdy enough to hold the new roof and the other issues that can go with the new roof. This is something that must be done correctly so hiring a professional is your best bet. There are problems with metal roof over shingles as mentioned above so you will want to take these into consideration.


Choosing to put a new roof on the house is a big decision and you want to make sure you make a good choice. The information above is all good reasons why NOT to put a new metal roof on top of shingles. However, it is always your own choice. Taking the time to really think your decision through and asking multiple professionals is a good idea. We can check your roof when we are conducting home inspections in the Atlanta, Ga. area.

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