metal roofing over asphalt shingles

Metal Roofing Over Asphalt Shingles: Is It a Good Idea?

Thinking about upgrading your roof? Metal roofing offers compelling advantages like durability and longevity, but the cost can be a significant hurdle. One way homeowners try to mitigate this cost is by installing a metal roof over their existing asphalt shingles. It sounds like a smart shortcut, right? Possibly. But it’s crucial to understand the implications before you commit. This comprehensive guide will walk you through the pros, cons, preparation steps, installation considerations, and long-term maintenance involved in installing a metal roof directly over asphalt shingles.

Understanding the Basics: Asphalt Shingles vs. Metal Roofing

Before we delve into the specifics of layering a metal roof over asphalt, let’s quickly recap the characteristics of each material. This will give you a solid foundation for understanding the potential benefits and drawbacks of this roofing approach.

Asphalt Shingles: The Traditional Choice

Asphalt shingles are the most popular roofing material in North America, and for good reason. They are relatively inexpensive, easy to install, and offer decent protection against the elements. There are two main types of asphalt shingles: 3-tab shingles and architectural (or dimensional) shingles.

3-Tab Shingles: These are the simpler, more affordable option. They have a uniform, flat appearance and typically last 15-20 years.

Architectural Shingles: Also known as dimensional or laminated shingles, these are thicker and more durable than 3-tab shingles. They offer a more textured, visually appealing look and can last 25-30 years or even longer.

The lifespan of asphalt shingles depends on factors like climate, installation quality, and shingle type. Regular maintenance, such as cleaning and addressing minor repairs, can extend their lifespan.

Metal Roofing: A Durable and Long-Lasting Alternative

Metal roofing is gaining popularity as homeowners seek more durable and long-lasting roofing options. Metal roofs come in various materials, including steel, aluminum, copper, and zinc. Each material has its own set of advantages and disadvantages in terms of cost, weight, corrosion resistance, and aesthetic appeal.

Steel Roofing: A common and cost-effective metal roofing option. It’s often coated with a protective layer (like galvanized or galvalume) to prevent rust. Steel roofs are strong and durable but can be heavier than other metal options.

Aluminum Roofing: Lighter than steel and naturally rust-resistant, making it a great choice for coastal areas. However, aluminum is generally more expensive than steel and may be more susceptible to dents.

Copper Roofing: A premium roofing material known for its beauty and exceptional longevity. Copper develops a distinctive green patina over time, adding to its visual appeal. Copper is one of the most expensive roofing materials.

Zinc Roofing: Similar to copper in terms of longevity, zinc is also a sustainable and environmentally friendly option. It develops a protective patina over time and is highly resistant to corrosion.

Metal roofs are known for their exceptional durability, often lasting 40-70 years or even longer with proper maintenance. They are also fire-resistant, energy-efficient (reflecting sunlight and reducing cooling costs), and can increase a home’s resale value.

The Appeal of Roofing Over Asphalt Shingles: Cost Savings and Convenience

The primary motivation for installing a metal roof over existing asphalt shingles is to save money and time. Removing the old shingles is a labor-intensive process that can add significantly to the overall cost of a new roof. By skipping this step, homeowners hope to reduce labor costs and disposal fees.

Beyond cost savings, there’s also the appeal of convenience. Removing an old roof is messy and disruptive. Installing a metal roof directly over the existing shingles minimizes the mess and disruption to your daily life.

Potential Benefits of Installing Metal Over Asphalt Shingles

While the practice isn’t universally recommended, there are potential advantages to installing a metal roof directly over asphalt shingles, provided certain conditions are met:

Cost Savings: As mentioned earlier, eliminating the tear-off process can significantly reduce labor costs and disposal fees.
Reduced Disruption: Installing over the existing roof minimizes mess and disruption to your home and surrounding property.
Added Insulation: The existing layer of asphalt shingles can provide an extra layer of insulation, potentially reducing energy costs.
Sound Dampening: The asphalt shingles can help to dampen the sound of rain or hail on the metal roof.
Protection of Underlayment: The old shingles act as a barrier, protecting the underlayment from the elements during the metal roof installation.

The Downside: Potential Problems and Risks

Despite the potential benefits, installing a metal roof over asphalt shingles comes with significant risks that you need to carefully consider. These risks can outweigh the initial cost savings if they lead to premature roof failure or other problems.

Hidden Damage: The Untouchable Truth

One of the biggest concerns is the potential for hidden damage beneath the asphalt shingles. Leaks, rot, or mold growth can be lurking unseen, and covering them up with a metal roof will only exacerbate the problem. This hidden damage can compromise the structural integrity of your roof deck and eventually lead to costly repairs.

Imagine this scenario: You have a small, slow leak in your existing roof. You don’t notice it because it’s not causing any visible damage inside your home. However, the leak is gradually rotting the wood sheathing underneath the shingles. If you install a metal roof over these damaged shingles, you’re essentially trapping the moisture and accelerating the rot. Over time, the weakened sheathing could collapse, requiring you to tear off both the metal roof and the asphalt shingles to make the necessary repairs.

Weight Concerns: A Heavy Burden

Adding a metal roof on top of asphalt shingles increases the overall weight load on your roof structure. While most roofs are designed to handle a certain amount of weight, adding an extra layer of roofing material can exceed this limit, especially if you already have multiple layers of asphalt shingles. This excessive weight can stress the roof framing and potentially lead to structural problems.

Before installing a metal roof over asphalt shingles, it’s crucial to have a structural engineer or qualified roofing contractor assess your roof’s load-bearing capacity. They can determine whether your roof can safely handle the added weight of the metal roof.

Reduced Lifespan: Shortchanging Your Investment

One of the main advantages of metal roofing is its longevity. However, installing it over asphalt shingles can shorten its lifespan. The asphalt shingles underneath can trap moisture and heat, which can accelerate corrosion of the metal roofing material. This is particularly true for steel roofing, which is susceptible to rust.

Furthermore, the uneven surface of the asphalt shingles can create gaps and pockets underneath the metal roof, which can trap debris and moisture. This can lead to premature wear and tear of the metal roofing panels.

Compromised Aesthetics: The Unseen Wrinkles

While a new metal roof will undoubtedly improve the appearance of your home, installing it over asphalt shingles can compromise its aesthetic appeal. The uneven surface of the shingles can create a wavy or uneven appearance in the metal roof, especially on roofs with multiple layers of shingles or shingles that are in poor condition. This can detract from the overall look of your home and potentially reduce its curb appeal.

Code Compliance: Legal Hurdles

Building codes vary by location, and some codes may prohibit or restrict the installation of metal roofing over asphalt shingles. Check with your local building department to ensure that your project complies with all applicable codes and regulations. Failure to comply with building codes can result in fines, stop-work orders, and even the need to remove the entire roof.

Warranty Issues: The Fine Print

Installing a metal roof over asphalt shingles can void the manufacturer’s warranty on the metal roofing material. Most manufacturers require that the metal roof be installed over a clean, solid surface to ensure proper performance and longevity. Installing it over asphalt shingles may be considered an improper installation, which can invalidate the warranty.

Before proceeding with the installation, carefully review the manufacturer’s warranty requirements to ensure that you are not jeopardizing your coverage.

When is Roofing Over Asphalt Shingles a Viable Option?

Despite the potential risks, there are situations where installing a metal roof over asphalt shingles may be a viable option. However, these situations are limited and require careful consideration and thorough preparation.

Single Layer of Shingles in Good Condition

If your existing roof has only one layer of asphalt shingles and the shingles are in relatively good condition (no significant damage, leaks, or rot), then installing a metal roof over them may be considered. However, it’s still crucial to inspect the roof deck for any signs of hidden damage before proceeding.

Professional Inspection and Assessment

Before making any decisions, have a qualified roofing contractor thoroughly inspect your roof. They can assess the condition of the shingles, the roof deck, and the underlying structure. They can also advise you on the best course of action based on your specific situation.

Proper Preparation and Installation Techniques

Even if your roof meets the criteria for installing metal over asphalt, proper preparation and installation techniques are essential. This includes:

Cleaning the Existing Roof: Remove any loose debris, moss, or algae from the surface of the asphalt shingles.
Installing a Vapor Barrier: A vapor barrier can help to prevent moisture from migrating from the asphalt shingles to the metal roof.
Using Furring Strips or Battens: Installing furring strips or battens between the asphalt shingles and the metal roof can create an air gap, which can help to improve ventilation and prevent moisture buildup. This is highly recommended.
Proper Fastening: Use the correct fasteners and fastening techniques to ensure that the metal roof is securely attached to the roof deck.

Preparing for a Metal Roof Installation Over Asphalt Shingles

If you’ve decided to proceed with installing a metal roof over asphalt shingles, proper preparation is key to minimizing the risks and maximizing the benefits. Here’s a step-by-step guide to preparing your roof:

Step 1: Thorough Inspection and Assessment

As mentioned earlier, the first step is to have a qualified roofing contractor thoroughly inspect your roof. They will assess the condition of the shingles, the roof deck, and the underlying structure. They will also check for any signs of leaks, rot, or mold growth.

The contractor should also evaluate the roof’s load-bearing capacity to ensure that it can safely handle the added weight of the metal roof.

Step 2: Cleaning and Repairing the Existing Roof

Once the inspection is complete, the next step is to clean and repair the existing roof. Remove any loose debris, moss, or algae from the surface of the asphalt shingles. Replace any damaged or missing shingles. Repair any minor leaks or cracks.

If there is significant damage to the shingles or the roof deck, it may be necessary to remove the shingles and repair the underlying structure before proceeding with the metal roof installation.

Step 3: Installing a Vapor Barrier (Recommended)

A vapor barrier is a thin layer of material that is designed to prevent moisture from migrating from the asphalt shingles to the metal roof. It is typically made of polyethylene or other waterproof material.

Installing a vapor barrier is highly recommended, especially in climates with high humidity or significant temperature fluctuations. It can help to prevent condensation from forming under the metal roof, which can lead to corrosion and other problems.

Step 4: Installing Furring Strips or Battens (Highly Recommended)

Furring strips or battens are strips of wood or metal that are installed between the asphalt shingles and the metal roof. They create an air gap that allows for ventilation and helps to prevent moisture buildup.

Installing furring strips or battens is highly recommended, as it can significantly improve the performance and longevity of the metal roof. It also helps to create a smoother, more uniform surface for the metal roofing panels.

Step 5: Planning the Installation

Before you start installing the metal roofing panels, take the time to plan the installation carefully. Measure the roof and calculate the amount of material you will need. Determine the best layout for the panels and plan the fastening pattern.

Also, make sure you have all the necessary tools and equipment on hand before you start the installation.

Installing the Metal Roof: A Step-by-Step Guide

Installing a metal roof is a complex process that requires specialized skills and knowledge. If you are not experienced in roofing, it is best to hire a qualified roofing contractor to do the job. However, if you are a skilled DIYer and you are comfortable working on roofs, you can attempt the installation yourself.

Here’s a general overview of the steps involved in installing a metal roof over asphalt shingles:

Step 1: Installing the Underlayment

Even with the existing shingles, it’s good practice to install a synthetic underlayment over the prepared surface. This provides an extra layer of protection against moisture and helps to create a smooth surface for the metal roofing panels.

Step 2: Installing the Drip Edge

Install a drip edge along the eaves and rakes of the roof. The drip edge is a metal flashing that helps to direct water away from the fascia and prevents it from seeping under the roofing material.

Step 3: Installing the Metal Roofing Panels

Start installing the metal roofing panels at the bottom of the roof and work your way up. Overlap the panels according to the manufacturer’s instructions. Use the correct fasteners and fastening techniques to ensure that the panels are securely attached to the roof deck.

Step 4: Installing the Ridge Cap

Install the ridge cap along the ridge of the roof. The ridge cap is a metal flashing that covers the seam between the two sides of the roof. It helps to prevent water from entering the attic.

Step 5: Flashing Around Penetrations

Properly flash around any roof penetrations, such as chimneys, vents, and skylights. Use flashing materials that are compatible with the metal roofing material.

Step 6: Final Inspection

Once the installation is complete, conduct a final inspection to ensure that everything is properly installed and that there are no leaks or other problems. Seal any gaps or cracks with caulk or sealant.

Long-Term Maintenance and Care

Even though metal roofs are known for their durability and longevity, they still require regular maintenance to ensure optimal performance. Here are some tips for maintaining your metal roof:

Regular Inspections: Inspect your roof at least twice a year, preferably in the spring and fall. Look for any signs of damage, such as dents, scratches, or corrosion.
Cleaning: Clean your roof regularly to remove any debris, moss, or algae. Use a soft brush and a mild detergent. Avoid using harsh chemicals or power washers, as they can damage the metal roofing material.
Trim Overhanging Branches: Trim any overhanging branches that could damage the roof.
Clear Gutters and Downspouts: Keep your gutters and downspouts clean and free of debris. Clogged gutters can cause water to back up under the roofing material, leading to leaks and other problems.
Repair Damage Promptly: Repair any damage to the roof promptly. Small repairs can prevent larger, more costly problems down the road.

Cost Considerations: A Detailed Breakdown

The cost of installing a metal roof over asphalt shingles can vary depending on several factors, including:

The Size and Complexity of the Roof: Larger and more complex roofs will require more materials and labor, which will increase the overall cost.
The Type of Metal Roofing Material: Different metal roofing materials have different costs. Steel is generally the most affordable option, while copper and zinc are the most expensive.
The Condition of the Existing Roof: If the existing roof is in poor condition, it may require more preparation and repair work, which will increase the cost.
The Labor Costs in Your Area: Labor costs vary by location. In general, labor costs are higher in urban areas than in rural areas.
Whether You Hire a Contractor or Do It Yourself: Hiring a contractor will add to the cost, but it will also ensure that the job is done correctly. Doing it yourself can save you money, but it also carries the risk of making mistakes.

Here’s a general breakdown of the costs involved in installing a metal roof over asphalt shingles:

Materials: The cost of the metal roofing materials will typically account for 40-60% of the total cost.
Labor: Labor costs will typically account for 30-50% of the total cost.
Preparation and Repair: The cost of preparing and repairing the existing roof can range from a few hundred dollars to several thousand dollars, depending on the condition of the roof.
Permits and Fees: You may need to obtain permits and pay fees to your local building department.

To get an accurate estimate of the cost of your project, it’s best to get quotes from several different roofing contractors.

Alternatives to Roofing Over Asphalt Shingles

If you’re concerned about the risks of installing a metal roof over asphalt shingles, there are several alternatives to consider:

Complete Tear-Off and Replacement: This is the most expensive option, but it also ensures that the job is done correctly and that your roof is in good condition. It involves removing the old asphalt shingles and installing a new metal roof over a clean, solid surface.
Installing a Metal Roof Over Existing Wood Sheathing: If your asphalt shingles are in poor condition, you can remove them and install a metal roof directly over the existing wood sheathing. This is a good option if the wood sheathing is in good condition and can provide a solid base for the metal roof.
Choosing a Different Roofing Material: If you’re not set on metal roofing, you could consider other roofing materials, such as asphalt shingles, tile, or slate. Each material has its own set of advantages and disadvantages in terms of cost, durability, and aesthetic appeal.

Making the Right Decision: Key Considerations

Ultimately, the decision of whether or not to install a metal roof over asphalt shingles depends on your individual circumstances and your risk tolerance. Here are some key considerations to keep in mind:

The Condition of Your Existing Roof: If your existing roof is in poor condition, it’s best to remove the shingles and start fresh.
Your Budget: Roofing over asphalt shingles can save you money in the short term, but it can also lead to costly problems down the road.
Your Long-Term Goals: If you plan to stay in your home for many years, it’s worth investing in a high-quality roofing system that will last for decades.
Your Local Building Codes: Make sure that your project complies with all applicable building codes and regulations.
The Manufacturer’s Warranty: Check the manufacturer’s warranty requirements to ensure that you are not jeopardizing your coverage.

By carefully considering these factors and weighing the pros and cons, you can make an informed decision about whether or not to install a metal roof over asphalt shingles. Remember to consult with a qualified roofing contractor to get professional advice and guidance.

Conclusion: Proceed with Caution

Installing a metal roof over asphalt shingles can seem like an attractive way to save money and time. However, it’s essential to be aware of the potential risks involved. Hidden damage, weight concerns, reduced lifespan, compromised aesthetics, code compliance issues, and warranty problems are all factors to consider. While there are situations where roofing over asphalt shingles may be viable, it requires careful assessment, proper preparation, and skilled installation.

Before making a decision, thoroughly inspect your existing roof, consult with a qualified roofing contractor, and weigh the potential benefits against the potential risks. Consider alternative roofing options if you have any doubts or concerns. A well-informed decision will ensure that you invest in a roofing system that provides long-lasting protection and enhances the value of your home.