Metal Roofing Over Asphalt Shingles: A Comprehensive Guide

The question of whether you can install metal roofing over asphalt shingles is a common one among homeowners looking for a durable and long-lasting roofing solution. The answer, in short, is often yes, but with several important considerations. This comprehensive guide will delve into the pros and cons of this approach, the necessary preparation, the installation process, and other crucial factors to ensure a successful and long-lasting metal roof.

Understanding the Basics: Why Consider Metal Over Asphalt?

Before diving into the specifics, it’s essential to understand why a homeowner might choose to install metal roofing over existing asphalt shingles. There are several compelling reasons, each offering distinct advantages.

Cost Savings

One of the primary drivers for choosing to install metal over asphalt is potential cost savings. Removing an existing asphalt shingle roof can be a labor-intensive and expensive undertaking. It involves tearing off the old shingles, disposing of the debris, and preparing the underlying roof deck for the new material. By installing the metal roof directly over the shingles, you can bypass these costs, potentially saving a significant amount of money.

Reduced Labor

Related to the cost savings is the reduction in labor required. Tearing off an old roof is a physically demanding job, and it can take several days or even weeks depending on the size and complexity of the roof. By eliminating this step, you significantly reduce the labor hours involved in the roofing project, which translates to lower labor costs if you’re hiring professionals.

Environmental Benefits

Leaving the existing asphalt shingles in place also has environmental benefits. Disposing of old roofing materials contributes to landfill waste, which is a growing concern. By avoiding the tear-off, you reduce the amount of waste generated and contribute to a more sustainable approach to roofing.

Added Insulation

The existing asphalt shingles can provide an additional layer of insulation, helping to improve the energy efficiency of your home. While the insulating value of asphalt shingles is relatively low (typically an R-value of around 0.44 per inch), every little bit helps to reduce heat transfer and lower your energy bills.

Noise Reduction

Asphalt shingles can also provide a small amount of noise reduction, helping to dampen the sound of rain or hail on the metal roof. While metal roofs are known for their durability, they can sometimes be noisier than other roofing materials. The underlying layer of asphalt shingles can help to mitigate this noise.

The Downsides: Potential Challenges and Considerations

While installing metal roofing over asphalt shingles offers several advantages, it’s crucial to be aware of the potential downsides and challenges. Careful consideration of these factors is essential to ensure a successful and long-lasting roofing system.

Added Weight

One of the primary concerns is the added weight on the roof structure. Metal roofing is generally lighter than asphalt shingles, but adding a layer of metal over an existing layer of shingles will increase the overall load. It’s crucial to have a structural engineer or qualified roofing contractor assess the roof’s capacity to handle the additional weight. If the roof structure is weak or damaged, it may need to be reinforced before installing the metal roof.

Moisture Trapping

Another significant concern is the potential for moisture trapping between the metal roof and the asphalt shingles. If moisture gets trapped, it can lead to rot, mold growth, and deterioration of the underlying roof deck. Proper ventilation is essential to prevent moisture buildup. This typically involves ensuring adequate airflow in the attic and using a breathable underlayment between the asphalt shingles and the metal roof.

Telegraphing

Telegraphing refers to the phenomenon where imperfections in the underlying asphalt shingles become visible through the metal roofing. This can be particularly noticeable if the shingles are old, warped, or uneven. Telegraphing can detract from the aesthetic appearance of the metal roof. To minimize telegraphing, it’s essential to ensure that the asphalt shingles are relatively flat and even before installing the metal roofing. This may involve repairing or replacing damaged shingles.

Reduced Lifespan

While metal roofs are known for their long lifespan, installing them over asphalt shingles can potentially reduce their longevity. The underlying asphalt shingles can trap heat, which can accelerate the degradation of the metal roofing material. In addition, if moisture gets trapped between the layers, it can corrode the metal and shorten its lifespan. Proper ventilation and a breathable underlayment are crucial to mitigate these risks.

Compatibility Issues

Not all metal roofing systems are compatible with all types of asphalt shingles. Some metal roofing systems require a specific type of underlayment or attachment method that may not be suitable for use over asphalt shingles. It’s essential to consult with a roofing manufacturer or qualified contractor to ensure that the chosen metal roofing system is compatible with the existing asphalt shingle roof.

Warranty Considerations

Installing metal roofing over asphalt shingles can sometimes void the manufacturer’s warranty on the metal roofing. Some manufacturers require that the metal roofing be installed directly over a clean, prepared roof deck in order to maintain the warranty. It’s crucial to check the warranty requirements of the metal roofing product you’re considering and to ensure that the installation method complies with those requirements.

Preparation is Key: Assessing the Existing Roof

Before installing metal roofing over asphalt shingles, thorough preparation is essential. This involves assessing the condition of the existing roof, making necessary repairs, and preparing the surface for the new roofing material.

Structural Inspection

The first step is to conduct a thorough structural inspection of the roof. This should be done by a qualified structural engineer or roofing contractor. The inspection should assess the overall condition of the roof structure, including the rafters, trusses, and sheathing. Look for signs of rot, water damage, sagging, or other structural problems. If any issues are identified, they must be addressed before proceeding with the metal roofing installation. This may involve reinforcing or replacing damaged structural members.

Shingle Condition Assessment

Next, assess the condition of the existing asphalt shingles. Look for signs of damage, such as missing shingles, cracked shingles, curled shingles, or granule loss. Pay close attention to areas that are prone to water damage, such as around chimneys, vents, and skylights. If a significant portion of the shingles are damaged, it may be necessary to remove them before installing the metal roofing. If only a few shingles are damaged, they can be repaired or replaced.

Surface Preparation

Once the structural inspection and shingle assessment are complete, it’s time to prepare the surface for the metal roofing. This involves cleaning the roof to remove any debris, such as leaves, branches, and dirt. You may also need to remove any loose or damaged shingles. If there are any significant imperfections in the surface of the shingles, such as large bumps or dips, you may need to level them out with a layer of roofing felt or plywood.

Ventilation Assessment

Proper ventilation is crucial to prevent moisture buildup under the metal roof. Assess the existing ventilation system to ensure that it provides adequate airflow in the attic. This typically involves checking the soffit vents, ridge vents, and gable vents. If the ventilation is inadequate, you may need to add additional vents to improve airflow. Consider installing a ridge vent system along the peak of the roof to provide continuous ventilation.

The Installation Process: Step-by-Step Guide

Installing metal roofing over asphalt shingles requires careful attention to detail and adherence to manufacturer’s instructions. Here’s a step-by-step guide to the installation process:

Step 1: Install Underlayment

The first step is to install a breathable underlayment over the asphalt shingles. This underlayment will act as a moisture barrier and help to protect the roof deck from water damage. Choose an underlayment that is specifically designed for use under metal roofing. Follow the manufacturer’s instructions for installation, ensuring that the underlayment is properly overlapped and sealed at the seams.

Step 2: Install Furring Strips (Optional)

In some cases, it may be necessary to install furring strips over the underlayment. Furring strips are wooden strips that are attached to the roof deck to create an air gap between the metal roofing and the asphalt shingles. This air gap helps to improve ventilation and prevent moisture buildup. If you choose to install furring strips, make sure they are properly spaced and attached to the roof deck.

Step 3: Install Metal Roofing Panels

The next step is to install the metal roofing panels. Start at the bottom edge of the roof and work your way up, overlapping the panels according to the manufacturer’s instructions. Use the appropriate fasteners to attach the panels to the roof deck or furring strips. Make sure the fasteners are properly spaced and tightened to prevent leaks.

Step 4: Install Trim and Flashing

Once the metal roofing panels are installed, it’s time to install the trim and flashing. This includes edge trim, ridge caps, and flashing around chimneys, vents, and skylights. The trim and flashing will help to seal the roof and prevent water from entering. Follow the manufacturer’s instructions for installing the trim and flashing.

Step 5: Inspect and Clean Up

After the metal roofing is installed, carefully inspect the roof for any leaks or imperfections. Make any necessary repairs and clean up any debris from the installation process.

Choosing the Right Metal Roofing System

There are several different types of metal roofing systems available, each with its own advantages and disadvantages. When choosing a metal roofing system for installation over asphalt shingles, it’s important to consider factors such as the climate, the style of your home, and your budget.

Standing Seam Metal Roofing

Standing seam metal roofing is one of the most popular types of metal roofing systems. It features vertical panels with raised seams that interlock to create a watertight seal. Standing seam metal roofing is durable, long-lasting, and energy-efficient. It’s a good choice for homes in areas with heavy snow or rain.

Metal Shingles

Metal shingles are designed to look like traditional asphalt shingles, but they are made of metal. Metal shingles are durable, fire-resistant, and low-maintenance. They are a good choice for homeowners who want the look of asphalt shingles with the durability of metal.

Corrugated Metal Roofing

Corrugated metal roofing is a more affordable option than standing seam or metal shingles. It features ribbed panels that are easy to install. Corrugated metal roofing is a good choice for outbuildings, sheds, and agricultural buildings.

Essential Tools and Materials

To successfully install metal roofing over asphalt shingles, you’ll need a variety of tools and materials. Here’s a list of the essentials:

• Metal roofing panels
• Breathable underlayment
• Furring strips (optional)
• Fasteners (screws or nails)
• Trim and flashing
• Roofing hammer
• Drill
• Measuring tape
• Chalk line
• Tin snips
• Safety glasses
• Gloves
• Ladder

DIY vs. Professional Installation

Installing metal roofing over asphalt shingles is a complex project that requires specialized knowledge and skills. While it’s possible to do it yourself, it’s generally recommended to hire a qualified roofing contractor. A professional contractor will have the experience and expertise to ensure that the job is done correctly and safely.

Benefits of Professional Installation

• Expertise and experience
• Proper tools and equipment
• Warranty protection
• Reduced risk of errors
• Faster completion time

Considerations for DIY Installation

If you choose to install metal roofing over asphalt shingles yourself, be sure to do your research and take the necessary safety precautions. Here are some important considerations:

• Thoroughly understand the installation process
• Obtain all necessary permits
• Wear appropriate safety gear
• Work with a helper
• Be prepared to spend several days or weeks on the project

Cost Factors: Estimating the Project Budget

The cost of installing metal roofing over asphalt shingles can vary depending on several factors, including the size of the roof, the type of metal roofing system, the complexity of the installation, and the cost of labor in your area. Here’s a breakdown of the key cost factors:

Materials Costs

The cost of the metal roofing panels, underlayment, fasteners, trim, and flashing will account for a significant portion of the overall project cost. The type of metal roofing system you choose will have a major impact on the material costs. Standing seam metal roofing is generally more expensive than metal shingles or corrugated metal roofing.

Labor Costs

If you hire a professional roofing contractor, labor costs will also be a significant expense. Labor costs can vary depending on the location and the experience of the contractor. Be sure to get multiple quotes from different contractors before making a decision.

Permit Fees

Most municipalities require a permit for roofing projects. The cost of the permit can vary depending on the location and the scope of the project.

Disposal Fees

If you need to dispose of any old roofing materials, you may need to pay disposal fees at a landfill or recycling center.

Maintenance and Longevity

Metal roofing is known for its durability and long lifespan. However, proper maintenance is essential to ensure that your metal roof lasts for many years. Here are some tips for maintaining your metal roof:

Regular Inspections

Inspect your metal roof regularly for any signs of damage, such as dents, scratches, or corrosion. Pay close attention to areas around chimneys, vents, and skylights.

Cleaning

Clean your metal roof periodically to remove any debris, such as leaves, branches, and dirt. You can use a garden hose or a pressure washer to clean the roof.

Repairing Damage

Repair any damage to your metal roof promptly to prevent further deterioration. Small dents and scratches can often be repaired with touch-up paint. More significant damage may require replacing the damaged panels.

Preventing Corrosion

To prevent corrosion, avoid using abrasive cleaners or tools on your metal roof. If you live in a coastal area, rinse your roof regularly with fresh water to remove salt buildup.

Conclusion: Is Metal Over Asphalt Right for You?

Installing metal roofing over asphalt shingles can be a cost-effective and environmentally friendly way to upgrade your roof. However, it’s essential to carefully consider the potential downsides and challenges before making a decision. Weigh the pros and cons, assess the condition of your existing roof, and consult with a qualified roofing contractor to determine if this approach is right for you. With proper preparation and installation, a metal roof over asphalt shingles can provide years of durable and reliable protection for your home.

Frequently Asked Questions (FAQ)

Q: Will installing metal roofing over asphalt shingles void my homeowner’s insurance?

A: It’s unlikely to automatically void your homeowner’s insurance, but it’s crucial to check with your insurance provider. Some policies may have specific requirements regarding roofing materials and installation methods. Informing your insurance company about the project beforehand ensures you remain covered in case of future roof-related issues.

Q: How much weight can my roof support?

A: This is a critical question that requires professional assessment. A structural engineer or experienced roofing contractor can evaluate your roof’s framing and determine its load-bearing capacity. Do not proceed with the installation without this assessment to avoid potential structural damage or collapse.

Q: What type of underlayment is best for metal roofing over asphalt shingles?

A: A breathable, synthetic underlayment is generally recommended. This type of underlayment allows moisture vapor to escape, preventing condensation and potential rot. Avoid using felt underlayment, as it can trap moisture.

Q: Can I install metal roofing over multiple layers of asphalt shingles?

A: Installing metal roofing over multiple layers of asphalt shingles is generally not recommended. The added weight can overload the roof structure, and it increases the risk of moisture trapping. It’s best to remove all existing layers of asphalt shingles before installing the metal roof.

Q: How long will a metal roof last when installed over asphalt shingles?

A: While metal roofs are known for their longevity, installing them over asphalt shingles can potentially reduce their lifespan. However, with proper ventilation and a breathable underlayment, you can still expect a metal roof to last for 40-70 years. Regular maintenance and inspections are essential to maximize its lifespan.

Q: What are the signs that my roof is not suitable for metal over asphalt?

A: Signs that your roof may not be suitable include: significant sagging, extensive rot or water damage, multiple layers of existing shingles, and a roof structure that is not strong enough to support the added weight. A professional inspection is crucial to determine suitability.

Q: Can I install solar panels on a metal roof installed over asphalt shingles?

A: Yes, you can install solar panels on a metal roof installed over asphalt shingles. However, it’s important to use a mounting system that is specifically designed for metal roofs. Consult with a solar panel installer to determine the best mounting option for your roof.

Q: Will a metal roof over asphalt shingles increase the value of my home?

A: Yes, a metal roof can increase the value of your home. Metal roofs are durable, long-lasting, and energy-efficient, which can make your home more attractive to potential buyers. However, the increase in value will depend on factors such as the location of your home, the condition of your home, and the demand for metal roofs in your area.

Q: How do I find a qualified roofing contractor for this type of project?

A: To find a qualified roofing contractor, ask for referrals from friends, family, or neighbors. You can also check online directories such as the Better Business Bureau or Angie’s List. Be sure to get multiple quotes from different contractors and check their references before making a decision. Verify their licensing and insurance to ensure they are qualified and reputable.

Q: What questions should I ask a roofing contractor before hiring them?

A: Here are some important questions to ask a roofing contractor:

• Are you licensed and insured?
• How many years of experience do you have?
• Do you have experience installing metal roofing over asphalt shingles?
• Can you provide references from past clients?
• What type of warranty do you offer?
• What is your estimated timeline for the project?
• What is the total cost of the project, including materials and labor?