Metal Roofing Over Asphalt Shingles: A Comprehensive Guide
The allure of a metal roof is undeniable. Its durability, longevity, and energy efficiency make it an attractive option for homeowners seeking a long-term roofing solution. However, the prospect of tearing off an existing asphalt shingle roof can be a daunting and expensive task. This leads many to consider the possibility of installing a metal roof directly over asphalt shingles. While seemingly a cost-effective shortcut, this approach requires careful consideration. This comprehensive guide will explore the various aspects of installing a metal roof over asphalt shingles, weighing the advantages and disadvantages, and providing insights to help you make an informed decision.
Understanding the Basics: Asphalt Shingles and Metal Roofing
Before delving into the specifics of installing metal roofing over asphalt shingles, it’s essential to understand the characteristics of each material.
Asphalt Shingles: A Familiar Choice
Asphalt shingles are the most common roofing material in North America, favored for their affordability, ease of installation, and variety of styles. They consist of a fiberglass or organic mat saturated with asphalt and coated with mineral granules for protection and aesthetic appeal. There are two primary types: three-tab shingles, known for their simple, uniform appearance, and architectural or dimensional shingles, which offer a more textured and visually appealing design. Asphalt shingles typically have a lifespan of 15 to 30 years, depending on the quality of the materials, climate conditions, and proper installation.
Metal Roofing: Durability and Longevity
Metal roofing encompasses a wide range of materials, including steel, aluminum, copper, and zinc. These materials are known for their exceptional durability, often lasting 50 years or more with proper maintenance. Metal roofs are also highly resistant to fire, wind, and impact damage, making them a robust choice for homes in harsh climates. Furthermore, metal roofing can be incredibly energy-efficient, reflecting solar radiation and reducing cooling costs in the summer. While the initial cost of metal roofing is typically higher than asphalt shingles, its long lifespan and reduced maintenance can make it a more cost-effective option over the long term.
The Pros and Cons of Installing Metal Roofing Over Asphalt Shingles
The decision to install a metal roof over asphalt shingles involves a careful evaluation of the potential benefits and drawbacks. While it may seem like a straightforward solution, it’s crucial to understand the implications of this approach.
Advantages: Streamlining the Installation Process
One of the primary attractions of installing metal roofing over asphalt shingles is the potential cost savings associated with eliminating the tear-off process. Removing an existing asphalt shingle roof can be labor-intensive and expensive, requiring the disposal of old materials. By installing the metal roof directly over the shingles, homeowners can potentially save on labor and disposal costs.
Another advantage is the added layer of insulation provided by the existing asphalt shingles. This can contribute to improved energy efficiency, reducing heating and cooling costs. The asphalt shingles can act as a thermal barrier, helping to maintain a more consistent temperature inside the home. However, the extent of this insulation benefit is often marginal.
Furthermore, installing a metal roof over asphalt shingles can be a quicker and less disruptive process compared to a full roof replacement. The elimination of the tear-off phase reduces the overall project timeline, minimizing inconvenience for homeowners. This can be particularly appealing for those who want to minimize the disruption to their daily lives.
Disadvantages: Potential Risks and Complications
While the prospect of saving time and money may be tempting, installing a metal roof over asphalt shingles also carries several potential risks and complications. One of the most significant concerns is the potential for moisture buildup between the two roofing layers. If moisture becomes trapped between the metal and asphalt, it can lead to corrosion of the metal roof, rot in the underlying roof deck, and the growth of mold and mildew. This can compromise the structural integrity of the roof and create unhealthy living conditions.
Another potential issue is the unevenness of the existing asphalt shingle roof. Over time, asphalt shingles can become warped, cracked, or otherwise damaged. Installing a metal roof over an uneven surface can create an uneven appearance and potentially compromise the performance of the metal roof. Any imperfections in the underlying shingles will telegraph through to the metal, diminishing the aesthetic appeal.
Moreover, installing a metal roof over asphalt shingles can void the manufacturer’s warranty for the metal roofing system. Many manufacturers require that metal roofs be installed directly onto a solid, clean roof deck to ensure proper performance and longevity. Installing over existing shingles may not meet these requirements, leaving homeowners without warranty protection in the event of a problem.
Furthermore, identifying and repairing roof leaks can become significantly more challenging when a metal roof is installed over asphalt shingles. The multiple layers of roofing material can make it difficult to pinpoint the source of a leak, leading to extensive and costly repairs. Finding the exact point of entry for water becomes akin to searching for a needle in a haystack.
Preparation is Key: Ensuring a Successful Installation
If you decide to proceed with installing a metal roof over asphalt shingles, proper preparation is crucial to minimize potential risks and ensure a successful installation. This involves thoroughly inspecting the existing roof, addressing any necessary repairs, and taking steps to mitigate moisture buildup.
Thorough Roof Inspection
Before beginning the installation process, it’s essential to conduct a thorough inspection of the existing asphalt shingle roof. This inspection should identify any areas of damage, such as cracked, missing, or warped shingles. It’s also important to check for signs of rot, mold, or water damage. Any damaged areas must be repaired or replaced before the metal roof is installed. Ignoring these issues will only exacerbate them over time and potentially compromise the integrity of the new roofing system.
Addressing Underlying Issues
Any underlying roof deck damage must be addressed before installing the metal roof. This may involve replacing rotted or damaged sheathing. It’s also important to ensure that the roof deck is properly secured to the rafters or trusses. A solid, stable roof deck is essential for providing a secure base for the metal roof.
Creating a Smooth and Even Surface
To ensure a smooth and even surface for the metal roof, it may be necessary to install a layer of underlayment over the existing asphalt shingles. This underlayment can help to fill in any gaps or imperfections in the shingles, creating a more uniform surface. It also provides an additional layer of protection against moisture penetration. A popular choice is a synthetic underlayment designed to breathe and allow moisture to escape.
Addressing Ventilation Concerns
Proper ventilation is crucial for preventing moisture buildup and maintaining a healthy roof system. When installing a metal roof over asphalt shingles, it’s essential to ensure that the existing roof ventilation system is adequate. This may involve adding additional vents to the attic or roof deck. Adequate ventilation helps to circulate air and prevent condensation from forming beneath the metal roof. Consider ridge vents, soffit vents, or gable vents to achieve optimal airflow.
Installation Techniques: Best Practices for Success
The installation technique used for installing a metal roof over asphalt shingles is critical to the success of the project. Proper installation techniques can help to minimize the risk of moisture buildup, ensure proper drainage, and maximize the lifespan of the roofing system.
Choosing the Right Metal Roofing System
Not all metal roofing systems are suitable for installation over asphalt shingles. Some systems, such as standing seam roofing, are designed to be installed directly onto a solid roof deck. Other systems, such as screw-down metal roofing, may be more suitable for installation over existing shingles. Consult with a qualified roofing contractor to determine the best metal roofing system for your specific needs.
Using Furring Strips or Battens
Installing furring strips or battens between the asphalt shingles and the metal roofing can create an air gap that allows for ventilation and drainage. This air gap helps to prevent moisture buildup and can extend the lifespan of the roofing system. The furring strips should be properly spaced and securely fastened to the roof deck.
Proper Fastening Techniques
Proper fastening techniques are essential for ensuring the structural integrity of the metal roof. The metal panels must be securely fastened to the roof deck using screws or nails that are specifically designed for metal roofing. The fasteners should be properly spaced and driven to the correct depth. Overdriving or underdriving the fasteners can compromise their holding power and lead to leaks.
Sealing and Flashing Details
Proper sealing and flashing are crucial for preventing water penetration around chimneys, vents, and other roof penetrations. Use high-quality sealants and flashing materials that are compatible with both the metal roofing and the asphalt shingles. Ensure that all flashing is properly installed and sealed to prevent water from seeping underneath the roofing materials.
Cost Considerations: Weighing the Expenses
While installing a metal roof over asphalt shingles may seem like a cost-effective solution, it’s important to carefully consider all of the associated costs before making a decision. This includes the cost of the metal roofing materials, installation labor, and any necessary repairs to the existing roof. It’s also important to factor in the potential long-term costs associated with maintenance and repairs.
Metal Roofing Material Costs
The cost of metal roofing materials can vary depending on the type of metal, the thickness of the metal, and the style of the roofing panels. Steel and aluminum are generally less expensive than copper or zinc. Standing seam roofing is typically more expensive than screw-down metal roofing. Obtain quotes from multiple suppliers to compare prices and find the best value for your money.
Installation Labor Costs
Installation labor costs can vary depending on the complexity of the roof, the experience of the contractor, and the geographic location. Installing a metal roof over asphalt shingles may be slightly less expensive than a full roof replacement, but the labor costs can still be significant. Get multiple quotes from qualified roofing contractors and compare their prices and services.
Repair and Preparation Costs
Don’t forget to factor in the cost of any necessary repairs to the existing roof. This may include replacing damaged shingles, repairing rotted sheathing, or reinforcing the roof deck. These repairs can add to the overall cost of the project. Be sure to include a contingency fund in your budget to cover any unexpected expenses.
Long-Term Maintenance and Repair Costs
While metal roofs are generally low-maintenance, they may still require occasional repairs or maintenance. This may include resealing flashing, replacing damaged panels, or removing debris from the roof. Factor in these potential long-term costs when evaluating the overall cost-effectiveness of installing a metal roof over asphalt shingles.
Local Building Codes and Regulations
Before proceeding with any roofing project, it’s essential to check with your local building codes and regulations. Some municipalities may have specific requirements for installing metal roofs over asphalt shingles. These requirements may include restrictions on the type of metal roofing that can be used, the installation techniques that must be followed, or the need for a building permit. Failure to comply with local building codes can result in fines or delays in the project.
Permitting Requirements
Many municipalities require a building permit for roofing projects. The permit application typically requires detailed plans of the proposed roofing system, including the type of metal roofing, the installation techniques, and the location of all roof penetrations. The building department may also conduct inspections to ensure that the roofing project complies with local building codes.
Weight Restrictions
Some building codes may have weight restrictions for roofing materials. This is particularly important when installing a metal roof over asphalt shingles, as the combined weight of the two roofing systems can be significant. Ensure that your roof structure can support the additional weight before proceeding with the project.
Fire Safety Regulations
Building codes typically have fire safety regulations for roofing materials. Metal roofs are generally considered to be fire-resistant, but it’s important to ensure that the metal roofing system meets the local fire safety requirements. This may involve using specific types of metal roofing or installing fire-resistant underlayment.
The Importance of Hiring a Qualified Roofing Contractor
Installing a metal roof over asphalt shingles is a complex project that requires specialized knowledge and skills. It’s crucial to hire a qualified roofing contractor who has experience with this type of installation. A qualified contractor can assess the condition of your existing roof, recommend the best metal roofing system for your needs, and ensure that the installation is done correctly. They can also navigate the local building codes and permitting requirements.
Finding a Reputable Contractor
When searching for a roofing contractor, it’s important to do your research. Get recommendations from friends, family, or neighbors. Check online reviews and ratings. Verify that the contractor is licensed and insured. Ask for references from past clients. Interview several contractors and compare their prices, services, and experience.
Verifying Credentials
Before hiring a roofing contractor, verify their credentials. Check their license with the state licensing board. Verify that they have adequate insurance coverage, including liability insurance and workers’ compensation insurance. Ask for proof of insurance before signing a contract.
Reviewing the Contract
Before signing a contract with a roofing contractor, carefully review all of the terms and conditions. Make sure that the contract includes a detailed description of the work to be performed, the materials to be used, the total cost of the project, and the payment schedule. Also, make sure that the contract includes a warranty for the workmanship and materials.
Alternatives to Installing Metal Over Asphalt
While installing a metal roof over asphalt shingles might seem appealing, it’s worth considering alternative options that might offer better long-term results and minimize potential problems. Two primary alternatives are a complete tear-off and replacement or considering other roofing materials.
Complete Tear-Off and Replacement
The most recommended approach is a complete tear-off of the existing asphalt shingles followed by the installation of the new metal roof directly onto the roof deck. This allows for a thorough inspection of the roof deck, addressing any hidden damage and ensuring a solid foundation for the new roof. While this option is typically more expensive upfront due to labor and disposal costs, it provides the best opportunity for a long-lasting, trouble-free metal roofing system. It also ensures that the manufacturer’s warranty remains valid.
Exploring Other Roofing Materials
If the primary motivation for considering metal roofing is durability and longevity but the cost is a concern, exploring alternative roofing materials might be beneficial. Options like slate, tile, or high-quality architectural asphalt shingles offer extended lifespans compared to traditional asphalt shingles and might be a more cost-effective solution than metal roofing, especially when considering the potential complications of installing metal over asphalt.
Conclusion: Making an Informed Decision
Installing a metal roof over asphalt shingles is a complex decision that requires careful consideration of the potential benefits and drawbacks. While it may offer some cost savings in the short term, it also carries potential risks, such as moisture buildup, uneven surfaces, and voided warranties. Before proceeding with this approach, it’s essential to thoroughly inspect the existing roof, address any necessary repairs, and consult with a qualified roofing contractor. Ultimately, the best decision will depend on your specific circumstances, budget, and long-term goals. If you’re unsure whether installing a metal roof over asphalt shingles is the right choice for you, consider the alternative options discussed above and weigh the pros and cons of each approach. Remember that investing in a properly installed and maintained roof is an investment in the long-term value and safety of your home.
