Regarding roofing options, homeowners often look for durable, cost-effective solutions. Metal roofs are famous for longevity and energy efficiency.
Shingle roofs are popular for several reasons, including affordability, ease of installation, a wide range of style options, and adequate protection against weather elements. They balance cost and durability, making them a common choice for residential roofing.
However, the practice of installing metal roofs over existing shingles is a topic that warrants careful consideration.
In this post, I will explain why you should not install metal roofs over shingles.
Let\’s get started.
Major problems installing metal roofs over existing shingles
Homeowners may choose to install metal roofs over existing shingles to save on the cost and time of shingle removal. This method can provide a quick and cost-effective way to upgrade the roof while maintaining the existing insulation.
However, installing metal roofs over shingles will cause issues. Some may not be visible immediately, but the problems will occur soon. I discussed the issues below.
Weight Considerations
Adding weight is one of the primary concerns with installing metal roofs over shingles.
While metal roofing materials are generally lighter than traditional asphalt shingles, the cumulative weight of multiple layers can exceed the load-bearing capacity of the roof structure. This can lead to structural issues, compromising the roof\’s integrity and potentially causing damage over time.
Read also: How to clean a shingle roof?
Ventilation Challenges
Installing metal roofing directly over shingles can impede proper airflow, trapping moisture between the layers. This can cause mold and mildew growth, compromising the insulation and causing potential health hazards for occupants.
Related: Active and passive ventilation – which one is the best for your roof
Reduced Energy Efficiency
Metal roofs have reflective sunlight and absorb hits, which helps maintain a cooler indoor environment.
However, when installed over shingles, this reflective quality may be compromised due to the uneven surface created by the underlying shingles. The diminished energy efficiency could increase utility bills as the roof may not reflect sunlight and heat effectively.
Related: Energy-efficient roofs: What they are & what to look for
Voided Warranties
Many metal roofing manufacturers provide warranties that are contingent on specific installation guidelines. Installing a metal roof over existing shingles might void these warranties, leaving homeowners without the expected protection.
It\’s crucial to check with the manufacturer and ensure that the chosen installation method complies with their warranty requirements.
Read also: 11 main reasons for denying roof insurance claims and solution
Potential for Trapped Moisture
Shingles are prone to wear and tear over time, and moisture can become trapped between the metal roof and the aging shingles.
This trapped moisture can lead to corrosion and premature deterioration of the metal roofing material, reducing its lifespan and effectiveness.
Read also: 10 essential tips for roof maintenance and repairs
Hard to Fix Roof Decking
Roof decking is the wooden boards and frames that are the main structure of your roof. It provides a base for roofing materials such as shingles or metal roofing.
When metal roofing is installed directly over shingles, the underlying condition of the roof decking is obscured. If there are issues with the decking, such as rot or damage, they may go unnoticed and unaddressed. Replacing rotten decking becomes challenging once the metal roof is in place.
Read also: How to remove mold from roof shingles?
Frequently asked questions
Yes, removing old shingles before installing a metal roof is recommended. Removing shingles allows for a thorough inspection of the roof decking, prevents potential weight issues, and ensures a smoother installation. It also helps address ventilation concerns and reduces the risk of trapped moisture, contributing to a more durable and practical metal roofing system.
Installing a metal roof over shingles might be initially cheaper due to labor and material savings, but potential long-term issues can lead to additional costs. Removing shingles and addressing underlying problems during installation may provide better value in the long run, even if the upfront cost is higher.
Metal roofs are less likely to leak when properly installed than shingle roofs. Metal roofs are durable and resistant to water penetration. However, the risk of leaks is influenced by installation quality, flashing details, and maintenance rather than the roofing material.
Conclusion
While metal roofing offers various advantages, installing it over existing shingles is a decision that requires careful consideration. Homeowners should weigh the potential drawbacks, such as added weight, ventilation challenges, reduced energy efficiency, voided warranties, and the risk of trapped moisture.
