HOW TO INSTALL METAL ROOF OVER SHINGLES: Step-by-Step Guide

So you need a new roof. You may have shingles now, but are they your best option in the future? Maybe, but have you thought about your other options? Metal roofing is one of the best options for any structure, including homes of all sizes. They are not only more visually appealing, but they are also far more durable than shingles. If you’re thinking about getting a metal roof, you might be wondering if you can install over shingles and what problems you might run into. Keep reading because we’ll answer that question in this blog.

Why Install Metal Roofing Over Existing Shingles?

Shingles are a low-cost roofing material, but they require regular maintenance and replacement. Consequently, many business owners simply tire of the constant expense, mess, and disruption to their business operations. Metal roofing offers building owners a way out of the shingle replacement cycle.

Metal roofing typically has a higher initial cost than new shingles, but it can last 50 years or more with minimal upkeep. (That’s easily 2-3 times the life of a shingle roof!) Because it is available in a wide range of styles and colors, a metal roof also adds curb appeal to a building.

Aside from durability and aesthetics, metal roofing is made of recycled materials and is 100% recyclable when it is no longer needed. So for building owners looking to be environmentally friendly, it’s tough to find a more eco-friendly roofing option than metal panels. Because shingles are rarely recycled, waste disposal companies and landfills frequently charge a high fee to accept them.

In contrast, installing a metal roof over existing shingles means that any shingle tear-off expenses, including disposal fees, are avoided entirely. The benefits of a metal roof are also yours.

Install a Metal Roof Over the Shingles

Asphalt shingles are the most common type of roofing in the United States. They’re simple to install, inexpensive, and do a good job—but metal roofing is far superior in terms of durability and longevity.

Why then do fewer Americans choose metal roofing? Many people believe that to transition to a metal roof, they must rip out their asphalt shingles. This could double the cost of the entire process. Many people are put off by the thought of metal roofing because it is already more expensive than shingles.

But there is some good news. It is possible to install a metal roof over shingles, which saves money while providing all of the benefits of a high-quality metal roof. Learn more about having to install metal roofing over shingles by reading our guide.

Steps to Installing a Metal Roof Over Shingles

Though there are many ways to install a metal roof over shingles, we recommend this installation method because it provides the most durability over time.

#1. Examine the Plywood

To ensure that the plywood beneath the asphalt shingles is in good condition, it is crucial to first inspect it. Before installing a new roof, it is essential to deal with any rotting or corrosion. If it’s in good condition, it’s safe to proceed.

#2. Install Synthetic Underlayment

Installing underlayment will help prevent asphalt shingle granules from collapsing against the new metal roof, which could cause damage over time. The majority of underlayment is made of felt, but we recommend synthetic underlayment because it will not tear when the metal roof expands and contracts.

#3. Add Insulation

A protective layer between the old asphalt roof and the metal roof will be created by adding E-foil insulation on top of the underlayment. By reflecting heat away from the roof in the summer, this layer can also improve energy efficiency.

#4. Install Corrugated Metal Panels

The metal roof is now the last step. Corrugated metal, which allows air to flow and creates a natural venting process, works best when combined with E-foil insulation.

Metal Roof Over Shingles Problems

Installing a metal roof over shingles sounds like a great idea because it is less messy and easier to add to the roof. Is it true, though? Yes, you will save money, but you will also be hiding dangers, which could cost you more money in the long run. Furthermore, shingles have a lifespan of 15-20 years, and covering them does not extend their life. All good things must come to an end. So here is some metal roof over shingles problems below:

#1. Missed Damage & Shortened Roof Lifespan

When choosing to install a metal roof over shingles, you are going to miss damage under the roof. For example, you might not be aware that there is wood rot. Also, are you certain the roof sheathing was replaced? This wood layer attaches to the roof’s trusses and joists and keeps water out. You want to assume it’s there, but if you have a water leak, you’ll know it’s rotting.

#2. Trapped Water Vapor and Moisture

Another problem with a metal roof over shingles is that moisture and water vapor can become trapped between the two layers of roofs, which is why the shingles should be removed. Unfortunately, it can result in new mold and rot if you don’t remove it. Removing it will also allow you to inspect the trusses and roof from inside the attic to identify any problems.

#3. Building Code Violation

Building codes in the state where the home is located may limit what you can do with your roof. Some states may allow you to add a layer on top of an existing roof, while others may not allow you to do so. If you go against the codes you can pay very hefty fines and have to replace your roof entirely.

#4. Issues 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 a metal roof is added, structural, foundational, or rotten wood issues will not go away. You will need to check for these before adding the new roof.

#5. Warranty May Be Void

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.

#6. Chalking and Fading

Chalking and fading of the paint can happen because of the UV rays on a house. In Georgia, in the southern part, the sunlight is very strong. The roof, however, can chalk and fade regardless of where you live. There is no specific time frame for this to occur, but many companies do provide a warranty for it.

#7. Leaky Roof Due to Installer Error

Sometimes problems are caused by the installer rather than the materials themselves. Unfortunately, we can order and get a great roof to put on the home, but if the installer makes errors, that is an issue. One of these issues is forgetting (or refusing to install) proper counterflashing on the roof next to the chimney to keep it from leaking.

Other problems that can occur include faulty seams, faulty fasteners, and failure to follow manufacturer instructions, to name a few. It is a good idea to have the roof inspected to ensure that it was properly installed.

Can you Put a Metal Roof Over the Shingles?

Yes, it’s possible to put metal roofing over shingles. However, before you begin your project, you must first check with your local building department to see if it is permitted. Some areas only permit re-roofing over one layer of shingles, while others permit re-roofing over two layers of shingles. Before beginning, you should be aware of the disadvantages of installing metal roofing over shingles. Contact your local roofing company to learn more and see what they can do for you.

Pros and Cons of Installing a Metal Roof Over Shingles

Depending on the size of your home or building, roofing installation can take several days. Should you hasten the process by installing a metal roof over your current 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 lower labor costs.
Increased insulation for your home or building as a result of additional roofing layers
A shorter project timeline because no time is required to remove the existing roofing materials.
More environmentally friendly because you won’t have to dispose of the asphalt shingles in a landfill.

Cons of Installing a Metal Roof Over Asphalt Shingles

Some building codes prohibit the installation of new roofing over existing roofing materials.
Asphalt shingle problems could have an impact on your new metal roof.
Moisture can become trapped between the asphalt shingles and the metal roof
Installing the metal roof over the existing shingles may void the warranty on it.

Factors to Consider Before Installing a Metal Roof Over Existing Materials

Based on the disadvantages of adding a metal roof without removing the old one, there are four factors to consider before deciding whether to install your metal roof over the existing one.

#1. Review building codes in your area

Building code violations can result in massive fines. In some areas, regardless of the roofing material you choose, you cannot install new roofing materials over old ones. Check your local building codes for more information on laying new materials over old ones before deciding on the best course of action for your project.

#2. Your current roof’s condition

If you leave the materials in place, old roofs with problems can cause problems with your new roof. You can make your roof problems worse by placing materials over them. The roof becomes too heavy for your structure is one issue you might encounter. If this occurs, you may experience buckling or sagging, which could result in severe structural damage.

#3. Determine whether moisture can be trapped between roofing materials.

A big reason people install metal roofs is that 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. Mold, mildew, and rot are still caused by moisture between your roofing materials.

#4. Check your roofing warranty language

Manufacturers of metal roofs may require that you install it directly onto your home, without any existing materials underneath. Failure to adhere to the installation guidelines may result in the voiding of your roofing material warranty. If you install your roof without first removing the old materials, your roofing contractor may refuse to provide a warranty on the installation work.

Can Metal Roofs be Installed Over Shingles?

In simplest terms: yes, you can install a metal roof over shingles. However, before making any decisions, you should consult with your local building department. Building officials will only allow a re-roof over one layer of shingles in some areas, while officials in other areas may allow you to place the roof over two layers of shingles. Fortunately, if you’re only going over one layer, it won’t be an issue in most places.

Do you need underlayment for a metal roof over shingles?

Yes, underlayment is required for all roofs. If you’re installing a metal roof over asphalt shingles, the shingles may be able to act as an underlayment for the roof. However, over time, the shingles’ expansion and contraction can cause damage beneath the metal roof. For this reason, it’s usually recommended that you remove the shingles on your home before installing a metal roof.

What is the best way to install a metal roof over shingles?

There are two methods for installing metal roofing over shingles. The initial step is to cover the old shingles with an approved underlayment. Although this is the method of installation that takes the least amount of time, it does not provide the flattest surface for metal roofing installation. Installing 1×4 purlins over the shingles is the second method. This is more expensive but of higher quality.

What is the advantage of a metal roof over shingles?

When it comes to installing metal over shingles, there are a couple of benefits. The first benefit is that it reduces the labor costs associated with shingles removal and keeps them out of landfills. The second benefit is that the shingles add an extra layer of insulation to your home. Metal roofs over shingles also present several problems. To learn more, contact your neighborhood roofing company.

Can you put a metal roof over 2 layers of shingles?

If you want to install metal roofing over two layers of shingles, you’ll need to check with your local building department. Many of them will only permit one or two layers of shingles. Contact your local roofing contractor to see what they can do for you if they allow it.

What are the two biggest concerns to a metal roof?

Problems with metal roofing:

Over-production—such as extreme pressure during the coiling of the metal.
Frequent stress from coil slitting (cutting) and roll-forming panels.
Inadequate space is provided for the thermal expansion and contraction of the panels.

How many layers of shingles can you put metal over?

One to two shingle layers can rest safely and securely under a metal roof. More than two layers may compromise the stability of your roof.

Conclusion

Choosing to put a new roof on the house is a big decision, and you want to make sure you make a good choice. All of the information presented above is persuasive evidence against installing a new metal roof over existing shingles. However, it is always your own choice. It is a good idea to give your decision some thought and to consult with multiple professionals.