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Common Problems With Installing A Metal Roof Over Shingles

Posted on June 18, 2024

metal roof over shingles problems

Many homeowners across the country may feel tempted to install a new metal roof over their old shingle one when getting a replacement. The main possible reason behind this is the potential cost savings. Many homeowners choose to install a new metal roof over existing shingles to avoid the expense of shingle tear off and disposal during the replacement process. But did you know that this method of roof renovation may result in even more roofing problems? 

There’s no doubt that metal roofs are durable, energy efficient, and long-lasting, and they provide one of the best possible roofing outcomes, but installing new metal roofing panels over an aging shingle can also pose risks. If you want to know the common problems that can occur when you install a metal roof over shingles, keep reading this blog post till the end. In it, we will disclose the problems that can occur in greater detail and the reasons behind them. 

Metal Roof Over Existing Shingles
Metal Roof Over Existing Shingles

The Appeal of Installing A Metal Roof Over Existing Shingles

Here are some reasons why installing a metal roof directly over shingles is an appealing choice to homeowners and business owners alike. 

1. Savings (No Tear-Off)

Cost savings is one of the most appealing aspects of installing a metal roof over existing shingles. This is because installing a metal roof over old shingles potentially saves you money on labor charges involved in tearing off and disposing of the existing shingles. By opting to install a metal roof on top of shingles, homeowners can eliminate the need for this preliminary step, thus saving the homeowner a substantial amount of money. 

2. Less Labor and Time 

Along with the cost savings, this simple roofing method results in reduced labor and time. While a complete tear-off requires a crew to spend extra days or weeks, depending on the size and complexity of your roof, this process can be completed more quickly since the installers only need to focus on adding the new layer. This efficiency not only reduces labor costs but also minimizes the disruption to your daily life. 

Overall, reduced costs and time needed for project completion are the most appealing reasons homeowners choose metal roofs over shingles. 

Common Problems With A Metal Roof Over Shingles 

While there are benefits to installing a metal roof over shingles, it’s important to be aware of the problems that can arise from doing so. Let’s explore these potential issues in detail to ensure you’re fully prepared.

1. Oil Canning 

One aesthetic issue to consider is the oil canning effect. Oil canning is a cosmetic concern that’s not directly associated with the roof’s functionality. This term describes the visible waviness or buckling that can occur on the surface of metal roofing panels. When installing a metal roof over existing shingles, the uneven surface of the old shingles roof can cause this effect to worsen. 

2. Trapped Moisture Between Layers  

With the practice of installing metal roofs over shingles, there is a high chance of trapped moisture between two layers. And since we know any damp place provides a thriving environment for mold spores to residue and spread, so this is itself a risk. 

3. Extra Weight On The Roof’s Structure 

Although metal roofing materials are relatively light, the combined weight of two roofing layers can strain the structural components of your home. If your roof structure is not designed to support this extra load, it could lead to issues such as sagging or even collapse in extreme cases.

4. Reduced Lifespan

The trapped moisture and the deteriorating shingles under the metal roof can potentially affect the new roof’s performance, increasing the chance of rotting and corrosion. This causes the lifespan of the new metal roof to be significantly shortened, leading to replacement quicker than expected. 

5. Voided Warranties

Some metal roof manufacturers won’t honor the material warranty if it’s installed over old shingles. They usually require that their roofing materials be installed on top of a clean, solid base such as a roof deck with adequate underlayment. So, if you don’t meet their requirements, you may be out of luck if something was to go wrong with the roof later on.

Installation Challenges

While it may seem like a quick job, installing a metal roof over shingles also presents several challenges that should not be overlooked. Consider the following factors before making a final choice. 

1. Proper Fastening Difficulties 

Securing the metal roof properly requires finding a solid surface for fastening. The existing shingles, which create an uneven surface, can make this task more difficult. 

2. Risk of Under-Driving Screws 

There is also a risk of under-driving screws, which means the screws are not driven in far enough to secure the metal panels in place. This can result in loose panels that rattle in the wind, allowing water to seep in and cause damage. 

3. Flashing and Sealing Complexities 

Because the existing shingles can interfere with the placement and effectiveness of flashing, sealing around vents, chimneys, and other roof penetrations can be more complex when adding a metal roof over shingles. This can pose water infiltration problems on the roof. 

Best Alternative: Complete Tear-Off

Given the potential challenges that can occur with installing a metal roof over shingles, you might wonder if there’s a better alternative. The best option is to perform a complete tear-off before installing the new metal roof.

1. Structural Safety

Starting fresh with a complete tear-off may seem expensive at first, but it provides some great advantages. It lets you inspect the roof deck and underlayment thoroughly, which is crucial to ensure that the roof is structurally sound and ready for the new roofing material. This approach also avoids a lot of issues that can come up when installing a metal roof over old shingles, like trapping moisture and not fastening the panels in place properly.

2. Long-Term Cost-Effectiveness

Although a complete tear-off involves higher initial costs, it can be more cost-effective in the long run. By addressing any underlying issues and providing a clean surface for the new roof, you are likely to enjoy a longer lifespan and better performance from your metal roof.

Metal Roof Over Shingles: A Good or Bad Choice?

The blog post has addressed the potential problems that can arise when installing metal roofs over existing shingles. However, metal roofs over shingles can be the right choice if you are tight on budget or looking for a quick fix to renovate your roof. However, it is important to weigh the benefits of cost savings and reduced environmental impact against the potential problems and installation challenges. 

Contact Expert Roofers In Wisconsin For Quality Metal Roof Installation

Whether you want to replace your roof or install new materials over existing ones, it is always best to consult a roofing professional. Contact the expert roofers at Prestige Roofing LLC in Wisconsin for your roofing needs. The roofers at our company will help you make the right choice depending on the current state of your roof and the weather conditions in your area. 
Upon a thorough inspection of your roof, we will help you make a choice that matches your roofing needs without affecting your financial goals. Contact us today at (920) 791-0414 and consult with one of our roofing professionals.