installing metal roof over asphalt shingles

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Installing a Metal Roof Over Asphalt Shingles: A Comprehensive Guide

Installing a Metal Roof Over Asphalt Shingles: A Comprehensive Guide

So, you’re thinking about installing a metal roof over your existing asphalt shingles? It’s a smart move! Metal roofs are durable, energy-efficient, and can significantly boost your home’s curb appeal. But before you jump in headfirst, let’s break down the process. This comprehensive guide will walk you through everything you need to know, from assessing your current roof to the final installation steps. We’ll cover the pros and cons, required materials, potential challenges, and crucial safety precautions. Consider this your one-stop resource for a successful metal roof overlay project.

Why Consider a Metal Roof Over Asphalt Shingles?

Let’s start with the “why.” Why would you even consider putting a metal roof over your existing asphalt shingles? The answer lies in a combination of cost-effectiveness, convenience, and long-term benefits.

Reduced Installation Costs

One of the biggest advantages is the potential to save money on labor costs. Tearing off your old asphalt shingles can be a time-consuming and expensive process. By installing the metal roof directly on top, you eliminate this step, significantly reducing the overall installation time and cost. You avoid disposal fees associated with the old shingles, which can add up quickly depending on your location.

Minimized Disruption

A roof replacement can be a major disruption to your household. Tearing off the old roof creates noise, dust, and potential for debris to fall around your property. Installing a metal roof over shingles minimizes these disruptions, allowing you to maintain a more normal living environment during the project.

Added Insulation and Soundproofing

The existing asphalt shingles act as an additional layer of insulation, potentially improving your home’s energy efficiency. They can also help dampen sound from rain, hail, or other external noises. While the effect might not be as dramatic as dedicated insulation, it’s a definite bonus.

Extended Roof Lifespan

A properly installed metal roof can last for 50 years or more. By adding it over your existing shingles, you essentially create a double-layered protective barrier against the elements, further extending the lifespan of your entire roofing system. The metal roof shields the asphalt shingles from direct sunlight, rain, and snow, preventing premature degradation.

Increased Home Value

A metal roof is a significant selling point for potential homebuyers. It’s a durable, long-lasting, and aesthetically appealing upgrade that can increase your home’s value and make it more attractive to buyers. The lower maintenance requirements of a metal roof compared to asphalt shingles are also a major plus.

Potential Drawbacks and Considerations

While installing a metal roof over asphalt shingles offers many advantages, it’s important to be aware of the potential drawbacks and considerations before making a decision.

Weight Considerations

Metal roofs are generally lighter than asphalt shingles, but adding a metal roof on top of existing shingles will increase the overall weight load on your roof structure. It’s crucial to have a structural engineer or qualified roofing contractor assess your roof’s load-bearing capacity to ensure it can handle the additional weight. Ignoring this step could lead to serious structural problems down the road.

Moisture Trapping

One of the biggest concerns with installing a metal roof over shingles is the potential for moisture to become trapped between the two layers. This trapped moisture can lead to mold growth, wood rot, and premature deterioration of both the shingles and the underlying roof deck. Proper ventilation is absolutely essential to mitigate this risk.

Telegraphing

Telegraphing refers to the phenomenon where imperfections in the underlying asphalt shingles become visible through the metal roofing. This can be especially noticeable with textured or uneven shingles. While it doesn’t necessarily compromise the structural integrity of the roof, it can affect the aesthetic appearance. A proper underlayment can help minimize telegraphing.

Building Codes and Permits

Building codes vary from region to region, and some codes may prohibit installing a metal roof over existing shingles. It’s essential to check with your local building department to ensure that your project complies with all applicable regulations and to obtain any necessary permits. Ignoring building codes can result in fines and require you to remove the entire roof.

Warranty Implications

Installing a metal roof over existing shingles may void the manufacturer’s warranty on the metal roofing materials. Be sure to carefully review the warranty terms and conditions before proceeding with the installation. Some manufacturers may require a specific type of underlayment or installation method to maintain the warranty.

Roof Deck Inspection is Crucial

Even if you’re not tearing off the old shingles, a thorough inspection of the roof deck is still crucial. Look for signs of rot, water damage, or structural weakness. Any damaged areas must be repaired before installing the metal roof. Ignoring these issues can compromise the integrity of the entire roofing system.

Is Your Existing Roof Suitable for a Metal Overlay?

Not all roofs are created equal, and not all are suitable for a metal roof overlay. Here’s what to look for:

Roof Deck Integrity

The roof deck, typically made of plywood or OSB, must be in sound condition. Check for soft spots, rot, or water damage. Walk around on the roof to feel for any areas that give way or feel spongy. If the deck is compromised, it needs to be repaired or replaced before proceeding.

Shingle Condition

The existing asphalt shingles should be relatively flat and even. Multiple layers of shingles, severely curled or damaged shingles, or significant granule loss can create an uneven surface that will telegraph through the metal roofing. A single layer of asphalt shingles is generally preferred for a metal overlay.

Roof Slope

Metal roofs require a minimum roof slope for proper water runoff. Check the manufacturer’s specifications for the recommended slope for your chosen metal roofing material. A roof that is too flat may not be suitable for a metal overlay.

Proper Ventilation

Adequate ventilation is essential to prevent moisture buildup under the metal roof. Ensure that your attic is properly ventilated with soffit vents and ridge vents or other ventilation systems. Consider adding additional ventilation if necessary.

Professional Inspection

The best way to determine if your roof is suitable for a metal overlay is to have it inspected by a qualified roofing contractor. They can assess the condition of the roof deck, shingles, and ventilation system and provide you with expert advice.

Tools and Materials You’ll Need

Once you’ve determined that your roof is suitable for a metal overlay, you’ll need to gather the necessary tools and materials.

Safety Equipment

  • Safety glasses
  • Work gloves
  • Hard hat
  • Roofing boots with good traction
  • Safety harness and lifeline

Tools

  • Measuring tape
  • Chalk line
  • Tin snips or metal shears
  • Drill with various drill bits
  • Impact driver
  • Hammer
  • Caulking gun
  • Seam crimper (for some metal roofing systems)
  • Ladder
  • Scaffolding (optional, but recommended for larger projects)

Materials

  • Metal roofing panels or shingles
  • Underlayment (synthetic or felt)
  • Fasteners (screws or nails)
  • Flashing (for chimneys, vents, and valleys)
  • Sealant or caulk
  • Ridge cap
  • Valley flashing (if needed)
  • Drip edge
  • Starter strip

Step-by-Step Installation Guide

Now, let’s get into the actual installation process. Remember, this is a general guide, and specific instructions may vary depending on the type of metal roofing system you choose. Always refer to the manufacturer’s instructions for detailed guidance.

Step 1: Prepare the Roof Surface

Before you start installing the metal roofing, you need to prepare the roof surface. This involves cleaning the shingles and making any necessary repairs.

  1. Remove any loose debris, such as leaves, branches, or moss.
  2. Sweep the roof surface with a broom to remove dirt and dust.
  3. Inspect the shingles for any damage, such as loose or missing shingles. Repair or replace any damaged shingles as needed.
  4. Address any areas of pooling water. Ensure proper drainage and consider adding additional underlayment in these areas.

Step 2: Install Underlayment

The underlayment provides an additional layer of protection against moisture and helps create a smooth surface for the metal roofing. Choose a high-quality synthetic underlayment or felt underlayment that is compatible with metal roofing.

  1. Start at the eave (bottom edge) of the roof and roll out the underlayment horizontally, overlapping each course by the manufacturer’s recommended amount (typically 6 inches).
  2. Secure the underlayment to the roof deck with staples or roofing nails.
  3. Continue rolling out the underlayment until you reach the ridge (top edge) of the roof.
  4. Overlap the underlayment at the ridge by at least 12 inches.
  5. Pay special attention to valleys and around roof penetrations like chimneys and vents. Use additional underlayment to create a waterproof seal.

Step 3: Install Drip Edge

The drip edge is a metal flashing that is installed along the eave and rake (sloping edge) of the roof. It helps to direct water away from the fascia and protects the edges of the roof deck.

  1. Install the drip edge along the eave, overlapping each piece by a few inches.
  2. Secure the drip edge to the roof deck with roofing nails.
  3. Install the drip edge along the rake, overlapping each piece and securing it with roofing nails.

Step 4: Install Starter Strip

The starter strip is a metal piece that is installed along the eave to provide a consistent starting point for the first course of metal roofing panels or shingles.

  1. Install the starter strip along the eave, ensuring that it is aligned properly.
  2. Secure the starter strip to the roof deck with screws or nails, following the manufacturer’s instructions.

Step 5: Install Metal Roofing Panels or Shingles

This is the heart of the installation process. Follow the manufacturer’s instructions carefully for the specific type of metal roofing you are using.

  1. Start at the eave and work your way up to the ridge.
  2. Overlap each panel or shingle according to the manufacturer’s specifications.
  3. Secure the panels or shingles to the roof deck with screws or nails, using the appropriate fasteners for the type of metal roofing you are using.
  4. Ensure that the fasteners are driven in straight and flush with the surface of the metal roofing. Overdriving the fasteners can damage the metal and create a leak point.
  5. For standing seam metal roofing, use a seam crimper to crimp the seams together, creating a watertight seal.

Step 6: Install Flashing

Flashing is used to seal around roof penetrations, such as chimneys, vents, and skylights. It prevents water from entering the roof system and causing damage.

  1. Cut the flashing to the appropriate size and shape.
  2. Install the flashing around the roof penetration, overlapping the metal roofing panels or shingles.
  3. Seal the flashing with caulk or sealant to create a watertight seal.
  4. Ensure proper step flashing around chimneys by integrating it with both the roofing and the chimney brickwork.

Step 7: Install Ridge Cap

The ridge cap is a metal piece that is installed along the ridge of the roof to cover the gap between the two sides of the metal roofing.

  1. Install the ridge cap along the ridge, overlapping each piece by a few inches.
  2. Secure the ridge cap to the roof deck with screws or nails.
  3. Use sealant to seal the joints between the ridge cap pieces.
  4. Ensure proper ventilation under the ridge cap, typically through a vented ridge system.

Step 8: Clean Up

Once the installation is complete, clean up any debris and leftover materials from the roof and the surrounding area.

  1. Remove any excess fasteners, scraps of metal roofing, or packaging materials.
  2. Sweep the roof surface with a broom to remove any dirt or dust.
  3. Dispose of the waste materials properly.

Essential Safety Precautions

Roofing work is inherently dangerous. Safety should be your top priority. Here are some essential safety precautions to keep in mind:

Wear Proper Safety Gear

Always wear safety glasses, work gloves, a hard hat, and roofing boots with good traction. A safety harness and lifeline are essential for working on steep slopes.

Use Ladders Safely

Position the ladder on a stable surface and ensure that it is securely anchored. Extend the ladder at least 3 feet above the roof edge. Have someone hold the ladder while you are climbing up or down.

Be Aware of Weather Conditions

Avoid working on the roof in wet, windy, or icy conditions. These conditions can increase the risk of slips and falls.

Work with a Partner

It’s always safer to work with a partner. They can help you with lifting heavy materials, spotting potential hazards, and providing assistance in case of an emergency.

Take Breaks

Roofing work can be physically demanding. Take frequent breaks to avoid fatigue and prevent accidents.

Inspect Tools Regularly

Inspect your tools regularly to ensure they are in good working condition. Replace any damaged or worn tools.

Be Mindful of Overhead Power Lines

Be extremely careful when working near overhead power lines. Maintain a safe distance to avoid electrocution.

Don’t Overreach

Avoid overreaching when working on the roof. Move the ladder or scaffolding as needed to stay within a comfortable and safe reach.

Maintaining Your Metal Roof

Once your metal roof is installed, proper maintenance will help extend its lifespan and keep it looking its best.

Regular Inspections

Inspect your roof at least twice a year, preferably in the spring and fall. Look for any signs of damage, such as loose fasteners, dents, or corrosion. Address any issues promptly to prevent them from becoming more serious.

Clean Debris

Remove any debris, such as leaves, branches, or moss, from the roof surface. This will help prevent moisture buildup and keep the roof looking clean.

Trim Overhanging Branches

Trim any overhanging branches that could potentially damage the roof or deposit debris on the surface.

Clean Gutters and Downspouts

Keep your gutters and downspouts clean to ensure proper water drainage. Clogged gutters can cause water to back up under the roof and damage the roof deck.

Repair Damage Promptly

If you notice any damage to your metal roof, such as loose fasteners, dents, or corrosion, repair it promptly to prevent it from worsening.

Consider Professional Maintenance

Consider hiring a professional roofing contractor to perform regular maintenance on your metal roof. They can identify potential problems early on and provide expert repairs.

Cost Considerations

The cost of installing a metal roof over asphalt shingles can vary depending on several factors, including the size and complexity of the roof, the type of metal roofing material you choose, and the labor costs in your area.

Materials

The cost of metal roofing materials can range from $100 to $300 per square (100 square feet), depending on the type of metal, gauge, and finish. Underlayment, fasteners, flashing, and other materials will add to the overall cost.

Labor

Labor costs can range from $200 to $500 per square, depending on the complexity of the project and the experience of the roofing contractor. If you choose to install the roof yourself, you will save on labor costs but you will need to factor in the cost of renting or purchasing any necessary tools.

Permits

You may need to obtain a building permit before installing a metal roof. Permit fees can vary depending on your location.

Removal and Disposal (if necessary)

If you decide to remove the existing asphalt shingles, you will need to factor in the cost of disposal fees, which can vary depending on your location and the amount of waste.

It’s always best to get multiple quotes from qualified roofing contractors to get an accurate estimate of the cost of your project. Be sure to ask for a detailed breakdown of the costs, including materials, labor, permits, and disposal fees.

Finding a Qualified Roofing Contractor

If you’re not comfortable installing a metal roof yourself, it’s best to hire a qualified roofing contractor. Here are some tips for finding a good contractor:

Get Referrals

Ask friends, family, or neighbors for referrals to reputable roofing contractors.

Check Online Reviews

Read online reviews on websites like Google, Yelp, and Angie’s List to get an idea of the contractor’s reputation and quality of work.

Verify Licensing and Insurance

Make sure the contractor is properly licensed and insured. This will protect you in case of accidents or damage to your property.

Get Multiple Quotes

Get quotes from at least three different contractors and compare their prices, services, and warranties.

Ask Questions

Don’t be afraid to ask the contractor questions about their experience, qualifications, and the materials they use.

Read the Contract Carefully

Before signing a contract, read it carefully and make sure you understand all the terms and conditions.

Conclusion

Installing a metal roof over asphalt shingles can be a worthwhile investment, offering long-term benefits in terms of durability, energy efficiency, and aesthetics. However, it’s essential to carefully consider the potential drawbacks, assess the condition of your existing roof, and follow proper installation procedures. Whether you choose to DIY or hire a professional, prioritizing safety and following manufacturer’s instructions are crucial for a successful and long-lasting metal roof.