If you are a homeowner looking for ways to renovate your home or commercial space, you must have thought about putting a metal roof over your roof shingles.
While a metal roof is a durable way to protect your roof from all kinds of damage, some metal roof over shingle problems must be evident when you first put a metal roof over shingles.
A metal roof is a durable, strong, and elegant roof that you can put over your top to give it much-needed protection from sunlight, hail, and harsh weather conditions.
When building a house, deciding which material to use as a roof over your shingles is crucial. But metal roofs come with their own set of problems.
While there are numerous benefits of installing therefore, roofs, people often want to put these metal roofs over shingles. Consequently, they must be aware of the metal roof over shingle problems we will explore.
Read on to discover the most common metal roof-over-shingle problems and how they can be fixed.
Common Metal Roof over Shingle Problems
While putting a metal roof over your asphalt shingles may sound like a good and inexpensive idea, there are some potential problems with metal roofs on shingles that no one notices until it is too late.
Let us explore the most common issues of installing metal roofs over asphalt roof shingles:
1. Susceptibility to Corrosion
Many people opt for metal roofs because they believe they defend against corrosion for a long. However, a galvanized metal roof is highly susceptible to decay over a certain period.
The main reason why corrosion and rust occur on a metal roof is water seepage.
Rusting occurs when oxygen and pollutants in the air combine with the moisture on rooftops, and this rust eats away the metal roof, corroding it along the way.
In addition, as a result of corrosion, the asphalt roof shingles below are exposed to sunlight and hail, causing them to get damaged sooner.
Although most metal roofs are covered with a water-resistant paint and protective coating that resists corrosion, there are still some instances where corrosion can occur:
Corrosion on the underside
Corrosion can occur if the coating on the underside of the metal roof is not done correctly.
This corrosion occurs when molecules of water get trapped between the metal panel and the underlayment of the top, causing the metal to weaken and lose its strength.
Corrosion on the underside of the metal roof can also happen if installed directly over a shingle roof, as it could scratch the protective coating, causing the metal roof to rust.
Saltwater Corrosion
This type of corrosion is most commonly seen on roofs close to the coast as there is an effect of saltwater on metal.
To avoid saltwater corrosion, it is important to choose different types of metal, such as aluminum and zinc, that do not rust easily due to saltwater.
Interaction between dissimilar metals
Often, metal roofs are made of a combination of dissimilar metals, which might have a negative interaction, which can cause early corrosion of the metal roof.
Corrosion on cut edges
Sometimes, corrosion may occur on the cut edges of a metal roof if they are not adequately covered with paint.
However, many metal roofs come with hemmed or folded edges that hide the cut edges of the metal.
Still, some corrosion can occur on these edges that can spread to the flat sides of the metal roof.
2. Chance of missing the damage on roof shingle
If you install a metal roof over asphalt shingles directly, you will probably miss the damages that have already occurred on your roof shingles.
This is because roof decking, or the wooden boards that are the foundation of the roof system, must be replaced and checked for any damages before a new roof is installed.
However, if you install a metal roof over your asphalt roof shingles, you must inspect the roof decking.
If you missed the chance to inspect any damage on the roof decking, such as broken or rotting boards, it might reduce the lifespan of your roof, resulting in faster rotting and deterioration.
In addition, the wood underneath the metal roof might rot and lead to water leaking, causing further damage to your roof.
Although putting a metal roof over your asphalt shingle might save you some cost, you will pay more in the end due to the unnoticed damages on the shingles.
Furthermore, the roof decking is not visible from the exterior, so pointing out any issues is much more challenging.
3. Trapped moisture and leakage
Another widespread problem that can occur when putting a metal roof over shingles is the trapped moisture and water that can cause corrosion and rot on the roof shingles, reducing the roof’s lifespan.
Leakages can also occur, causing damage to the roof shingle. Sometimes, leakages can still occur despite having metal roof-over-roof shingles.
This leakage is mainly due to uncontrollable events such as heavy rain or snow, wind, or structural damage.
However, some installation errors could be the cause of roof leakages. These are:
- The fasteners are not installed properly: the screws that fasten a metal roof over the roof shingles may be too tight or loose, causing water to enter the open spots.
- Improper seaming: The seams are sided ribs where metal roof panels meet the roof shingles. Due to an installation error, these seams may need to be correctly installed, and water could enter between these seams.
- Damaged sealants are coatings that seal out water, dirt, or other debris by forming a protective layer on the surface. In cases where the sealant is damaged or not correctly spread out on the metal roof, it can cause water to seep through and damage the inner lining.
4. Weight of the metal roof
A metal roof is a durable and robust material for covering roof shingles.
Still, before you decide to put a metal roof over the asphalt roof shingle, you must inspect whether your roof decking can handle the new metal roof.
The shingle roof is quite heavy, and installing a metal roof over it will likely increase its weight considerably.
The extra weight can cause the roof shingles to bend or buckle under the weight, leading to problems for the roof decking.
Although severe structural damage to the asphalt roof is not possible immediately unless the roof decking is already in terrible shape, it can still cause the roof decking to weigh down under the extra weight.
This weight can become a severe problem if the roof decking is already in bad shape and rotting due to water leakage.
If your roof has architectural shingles already installed, adding a metal roof will add too much weight to the top, causing it to sag in places that can be dangerous.
5. Metal roofs can easily get scratched
Metal panels and roofs are not scratch-resistant as asphalt roofs and can quickly become scratched.
Furthermore, metal panels can get scuffed or marked with time due to overgrown tree branches, debris, and even snow. In addition, in hailstorms, the metal roofs can get punctured and could experience tears that may result in leakages.
Due to the susceptibility to scratches and dents, metal roofs must be inspected regularly for any repairs before this problem gets out of hand and fully experiences breakages and holes.
6. Oil Canning
Oil canning is an inherent problem that every metal roof or surface experiences. Oil canning is visible “wavy” areas on the metal roof’s surface.
It is also called elastic buckling or “stress wrinkling” of the metal surface.
Oil canning occurs in the first place for several reasons, such as extreme pressure during the metal coiling and lack of adequate space for thermal expansion and contraction of roof panels.
Although oil canning may seem like a structural issue, it has nothing to do with the building’s structural stability.
It occurs mainly because insufficient space allows for the metal to expand fully. The “waves” created from oil canning can leave significant spaces between the metal panels and the shingles, causing water to leak.
7. Inadequate heat absorption
Another problem with metal roofs is that metal roofs do not absorb heat compared to tops made of different materials.
This is why attics and rooms under metal roofs are hot and have a high temperature.
However, contractors and homeowners can use insulated material to cool the internal areas to make these roofs absorb more heat.
8. Chalking and Fading
Another potential problem with metal roofs is chalking and fading.
Chalking is the buildup of a white residue on a painted or coated metal panel and results mainly because of paint resin breaking down due to UV ray exposure.
As the name suggests, Fading occurs when the paint’s pigment breaks down due to UV rays, water, chemicals, or pollution.
Metal roofs are more susceptible to experiencing chalking and fading as compared to roofs made of other materials.
Although this chalking and fading are primarily due to the environment and substances that a roof is made up of, it can be reduced with the help of solid and good-quality paints that can protect the roof’s surface from fading up to a specific period.
9. Difficulty in replacement of roof components
Suppose you should have checked your roof decking and boards before installing a metal roof over your shingles. As a result, you might notice damages on your roof after some time has passed.
As metal roofs are installed with the help of experienced contractors and roof constructors, pulling and installing them again can be difficult.
Installing a metal roof over shingles leads to difficulties in replacing essential components of the top, which might have gotten damaged over time, such as roof decking boards and other materials.
The roof shingles may also be leaking due to some internal damage, and replacement of shingles for stopping these leakages is difficult if a metal roof is over the top.
10. The buildup of condensation and moisture on the metal roof
There are various types of metal roofs with different designs. Some metal roofs have sloping plans to let snow and water slide off.
However, flat roofs are susceptible to the buildup of condensation and moisture. This condensation will likely be more evident on your top if you live in a humid climate.
In addition, visible white spots may be visible where the water keeps on dripping, or there might be some discoloration around the shingle edges.
Condensation can be reduced from the metal roof by installing a proper underlayment on the metal roof.
Doing so will reduce the buildup of moisture that could cause damage to the roof shingle.
11. May be expensive
Although it depends mainly on the contractor and his quoted price, a metal roof can be more expensive than other roof materials.
Add this to the damages already in your roof decking, such as broken or damaged boards. Therefore, repair and installation costs may be more than your estimates.
This is why it is important to do proper research before installing metal roofs over asphalt roof shingles.
Advantages of putting metal roof over asphalt roof shingles
Although the cons outweigh the pros of installing a metal roof over asphalt shingles, there are some benefits of putting a metal roof over asphalt shingles that are given in detail below:
1. Requires less maintenance
Unlike roofs made of other materials, such as wood, metal roofs require less maintenance and can last longer than roofs made of different materials.
2. Resistance to fire and rot
Metal roofs are resistant to fire, one of the most significant advantages of installing a metal roof over shingles.
The fire threat is real and can cause irreparable damage to the top and rooms. Metal does not catch fire and is inflammable, which makes it a safe option for installment over asphalt shingles.
In addition, metal roofs are not easily susceptible to rotting and decay and have a longer lifespan than other roof materials.
3. Longer lifespan
As mentioned, metal roofs are more long-lasting and have a longer lifespan than other roofs.
This is because metal does not wear off and erodes quickly. This may be why many roof contractors opt to install a metal roof over roof shingles to increase the roof’s lifespan and keep it intact for a more extended period.
4. Light in weight
A metal roof often comprises a single or double layer of fused metal.
This means that, unlike other materials, the metal roof is light in weight and can be easily installed compared to different roofs.
5. Durable and strong
The durability of a metal roof is the most significant advantage of a metal roof over shingles.
If a contractor wants to increase the durability and strength of a roof, he only needs to install a metal roof over the existing shingles.
This would make the top more durable and strong, protecting it against harsh weather conditions and wear and tear.
6. Environmentally friendly
In addition to being lightweight, metal roofs are eco and environmentally friendly and do not have any waste.
Unlike wooden ceilings, which use wood for construction, metal roofs are eco-friendly and do not produce waste detrimental to nature.
7. Better insulation
Metal roofs also save energy bills in addition to being environmentally friendly. In addition, they provide the needed insulation, especially in areas that experience heavy snowfall.
8. Many design options
Unlike other materials, metal roofs come in various designs and shapes. Many metal roofs come with a sloping shape, while others are designed in a way to shed away rainwater.
Choosing a roof design that fits your style and aesthetic sense is the key to an aesthetically pleasing home.
Since metal roofs have a variety of designs, homeowners have a large choice to make their selections.
How to Fix Problems of Metal Roof Over Shingles?
Although there are some problems with installing a metal roof over roof shingles, with proper care and planning, these problems can be fixed.
A metal roof over shingles may have certain advantages and benefits, such as durability and strength, but the cons outweigh the pros of a metal roof.
Contractors and homeowners must follow these guidelines to fix the issues associated with installing a metal roof over asphalt shingles.
- Before installing the metal roof on top of the asphalt roof shingles, tighten the roof shingles with a stapler.
- To ensure no moisture seeps between the metal roof and the roof shingles, use an air compressor to remove all the extra humidity between the gaps.
- To ensure no damages occur after the installment of the metal roof, repair and replace all the broken shingles beforehand and scrutinize the shingles before installing the metal roof.
- To avoid moisture from seeping between the roof panels, install a ridge vent and mount some intake vents at the roof’s highest point to increase the airflow.
- If you detect leakage in the roof, trace the leak’s origin and source and fill it up with caulk or cement.
- Do routine checking on your roof to inspect and resolve any issues with the top.
- A vapor barrier is ideal for protecting the roof against seeping moisture. Ensure the vapor barrier is mounted between the roof panels so that no water comes between the metal roof and the shingles.
- To make the roof more durable, change the underlayer of the ceiling before installation. You can also paint it before installing it to make it more durable and long-lasting.
- To minimize the damages caused to the metal roof, lubricate the trusses and joints between the metal roof and the asphalt roof shingles.
- Make sure to seal all the gaps between the metal roof and asphalt shingles using rubber or sealants so that no moisture seeps through the cracks.
- To reduce the weight of the metal roof, use lightweight aluminum panels and wood shake shingles. This will reduce the shingle’s weight, preventing it from bending and sagging.
- Mount a braced roof truss or a rafter between roof panels to increase support between the metal roof and shingles.
- Add an underlayer of bitumen to reduce the over-burdening on the roof shingles and distribute weight evenly.
- Using a vacuum to blow dry the ridge to control the moisture on the roof shingles.
- To avoid damage from any debris, remove the dead leaves and other materials from the top of the roof.
- Use an enamel wood stain before installing the roof to prevent fungus and mold from growing.
- Use wide fasteners to screw them directly on the roof rafters for better strength and support.
- Suppose you need clarification on any issue concerning metal roof installation over roof shingles. In that case, it is always better to call an experienced contractor or construction worker to look over any problem with the metal roof.
- Be sure the contractor takes notice and closes inspection of any problems with your roof shingles before installing the metal roof over shingles. Ensure that all underlying issues are resolved before the metal roof is installed.
- Do your research before opting to choose a metal roof over your shingles. Choose a contractor willing to examine and check the metal roof in case of any damage.
Conclusion
A metal roof is a reliable, durable, and robust alternative to use on the top instead of wooden and other materials.
However, before you put a metal roof over asphalt or shingles, you must be aware of metal roof-over-shingle problems.
Knowing this will allow you to take appropriate steps before installing the roof over your shingles.
In this way, you can be sure of the durability and strength of your roof, irrespective of the weather conditions and other external factors.
Arthur is a skilled roof worker with over 10 years of experience in the industry. He started his career as an apprentice and worked his way up to become a foreman.
When he’s not working on roofs, John enjoys with his family or writing posts. He is also a passionate cyclist.