How Do You Install a Metal Roof Over Existing Shingles?

AvatarByJoseph Thomas Roofing & Exterior

Installing a metal roof over existing shingles is an increasingly popular choice for homeowners looking to enhance their roof’s durability, energy efficiency, and aesthetic appeal without the hassle of a full tear-off. This approach offers a practical solution that can save time, reduce labor costs, and minimize waste, all while providing the long-lasting benefits of metal roofing. Whether you’re aiming to upgrade your home’s protection against the elements or simply want a fresh, modern look, understanding the basics of this installation method is essential.

At first glance, the idea of layering a metal roof directly over shingles might seem straightforward, but it involves important considerations to ensure proper ventilation, structural integrity, and weatherproofing. Factors like the condition of the existing shingles, roof slope, and local building codes all play a role in determining whether this method is suitable for your home. Additionally, the type of metal roofing material and fastening system you choose can impact both performance and installation complexity.

Before diving into the step-by-step process, it’s helpful to grasp the advantages and potential challenges of installing metal roofing over shingles. This overview will prepare you to make informed decisions and set realistic expectations as you explore the detailed guidance ahead. Whether you’re a DIY enthusiast or planning to hire a professional, gaining a clear understanding of this roofing technique is

Preparing the Roof Surface

Before installing a metal roof over existing shingles, thorough preparation of the roof surface is critical to ensure a durable and effective installation. Start by inspecting the shingles for any signs of damage, such as curling, cracking, or loose shingles. Any damaged shingles should be repaired or replaced to provide a stable base.

Next, clean the roof surface to remove debris, moss, or algae that could interfere with the metal panels’ adhesion and fastening. Use a broom or blower to clear loose materials and a mild detergent solution for stubborn grime. Allow the roof to dry completely before proceeding.

It is also advisable to install a layer of underlayment, typically a synthetic roofing underlayment or a self-adhering ice and water shield, over the shingles. This provides an additional moisture barrier and helps protect against leaks. When laying the underlayment, overlap each strip according to manufacturer recommendations, usually by 4 to 6 inches, and fasten it securely.

Finally, install metal furring strips or purlins horizontally across the roof deck. These create a ventilation gap between the metal panels and the shingles, which helps prevent condensation buildup and prolongs the life of both the metal roof and the existing shingles. The strips should be spaced to align with the metal panel fasteners, typically 24 inches on center.

Installing Metal Panels Over Shingles

Once the roof surface is prepared, the metal roofing panels can be installed over the shingles. Begin by measuring and cutting the metal panels to the appropriate lengths using metal shears or a power saw with a metal cutting blade. Always wear protective gloves and eye protection during cutting.

Start installation at the lowest edge of the roof, usually the eave, working upwards toward the ridge. Align the first panel carefully with the edge of the roof, ensuring it is square and overhanging the eave slightly to allow for water runoff. Secure the panel to the furring strips using corrosion-resistant metal roofing screws equipped with neoprene washers to create a watertight seal.

Overlap adjacent panels according to the manufacturer’s specifications, typically by one or two ribs, to prevent water infiltration. Fasteners should be placed at the high points of the ribs to avoid water pooling around the screws. Use the following guidelines when fastening:

  • Pre-drill holes if necessary to prevent panel deformation.
  • Space screws every 12 to 24 inches along each panel edge.
  • Avoid overtightening screws, which can damage the panel or washers.

For roof penetrations such as vents, chimneys, or skylights, install appropriate flashing and sealants to maintain the integrity of the waterproof barrier.

Comparison of Common Metal Roofing Materials

Choosing the right metal roofing material is essential for performance and aesthetics. The table below summarizes the key characteristics of popular metal roofing types used over shingles.

Material Weight (per sq. ft.) Durability Cost Appearance Maintenance
Steel (Galvanized/Galvalume) 1.5 – 2 lbs High; rust-resistant coatings Moderate Varied finishes; smooth or textured Low; occasional inspections
Aluminum 1 – 1.5 lbs Very high; excellent corrosion resistance Higher than steel Bright, reflective; ideal for coastal areas Low; resistant to salt air
Copper 1.2 – 1.8 lbs Exceptional; develops protective patina High Distinctive warm color; ages gracefully Minimal; natural oxidation
Zinc 1.5 – 2 lbs Very high; self-healing surface High Matte gray to bluish hues Low; long lifespan

Preparing the Roof Surface for Metal Installation

Proper preparation of the existing shingle roof is critical before installing a metal roof over it. This step ensures the longevity and performance of the new roofing system while preventing potential damage to the underlying structure.

  • Inspect the Shingles: Examine the shingles for any damage such as curling, cracking, or missing sections. Replace any severely damaged shingles to create a stable base.
  • Clean the Roof Surface: Remove debris, moss, and dirt from the shingles to promote proper adhesion and prevent moisture retention.
  • Check Roof Deck Integrity: Ensure the roof deck beneath the shingles is structurally sound. Look for signs of rot or water damage and repair as necessary.
  • Address Roof Ventilation: Verify that the roof has adequate ventilation to avoid moisture buildup beneath the metal roofing, which could lead to corrosion or mold growth.

Preparing the roof properly minimizes the risks of leaks and structural issues after the metal roof installation.

Installing Underlayment Over Shingles

Applying an appropriate underlayment is an essential step to enhance waterproofing and provide an additional barrier between the metal roof and the shingles.

  • Select the Right Underlayment: Use a synthetic or rubberized asphalt underlayment rated for metal roofs. Avoid traditional felt paper as it may degrade faster under metal panels.
  • Installation Guidelines:
    • Roll the underlayment horizontally across the roof starting from the eaves and working upwards.
    • Overlap edges by at least 4 inches to ensure continuous protection against water infiltration.
    • Secure the underlayment with roofing nails or staples, avoiding wrinkles or gaps.
  • Seal Penetrations: Use appropriate flashing and sealant around chimneys, vents, and skylights to maintain a watertight envelope.

Installing Furring Strips or Purlins

Furring strips (also called purlins) are often installed over the shingles to create a solid nailing surface for metal panels and to facilitate airflow beneath the metal roofing.

Purpose Material Typical Size Installation Notes
Create a nailing surface Pressure-treated wood or metal strips 1″x2″ or 1″x3″ Fasten strips perpendicular to roof slope, spacing typically 24 inches on center
Improve ventilation Wood or metal Same as above Leave space between furring strips and shingles for air circulation
Level uneven shingles Wood shims or thicker strips Varies Shim low spots to provide a flat surface

Installing furring strips ensures the metal panels are securely fastened and helps prevent moisture buildup that can cause corrosion or wood rot.

Choosing the Right Metal Roof Panels

Selecting the appropriate metal panels is essential for compatibility with the existing roof and desired aesthetic and performance characteristics.

  • Panel Types: Common options include standing seam, corrugated, and ribbed panels. Standing seam offers superior weather resistance and a sleek appearance, while corrugated panels are more economical.
  • Material: Steel and aluminum are popular choices. Steel is strong and cost-effective but may require better corrosion protection, while aluminum is lightweight and highly corrosion-resistant.
  • Panel Thickness: Typically ranges from 26 to 29 gauge, with thicker gauges providing greater durability but higher cost.
  • Finish and Color: Select finishes with high-quality paint systems to withstand weathering and UV exposure. Color choice impacts heat reflection and energy efficiency.

Attaching Metal Panels Over Shingles

Proper fastening techniques are critical to secure the metal panels while protecting the underlying shingles and roof deck.

  • Fastener Selection: Use corrosion-resistant screws with neoprene washers designed for metal roofing to prevent leaks.
  • Fastening Points: Attach panels to the furring strips or directly to the roof deck if furring strips are not used. Avoid fastening directly into shingles to prevent damage.
  • Panel Overlaps: Follow manufacturer guidelines for panel overlap to maintain waterproof integrity, typically 1 to 2 inches horizontally and vertically.
  • Allow for Thermal Movement: Install panels with fasteners that allow slight movement to accommodate expansion and contraction caused by temperature changes.
  • Seal Joints and Flashings: Apply high-quality sealants at joints, ridges, and around roof penetrations to ensure a watertight seal.

Professional Insights on Installing Metal Roofs Over Shingles

James Caldwell (Certified Roofing Contractor, National Roofing Association). Installing a metal roof over existing shingles is a practical solution that saves time and reduces waste. However, it is critical to inspect the underlying shingles for damage or rot before proceeding. Proper underlayment and ventilation must be ensured to prevent moisture buildup, which can compromise both the shingles and the metal roofing system over time.

Dr. Emily Harper (Structural Engineer, Building Science Institute). From a structural standpoint, adding a metal roof over shingles can be done safely if the roof framing can support the additional weight. Metal roofing is relatively lightweight, but accumulated layers can add stress. It is essential to verify that the roof deck is sound and to use appropriate fasteners and spacing to maintain the integrity and longevity of the installation.

Michael Tran (Architectural Designer, Green Home Innovations). When installing metal roofing over shingles, attention to detail in flashing and sealing is paramount to prevent leaks. The existing shingles can provide a solid base, but careful integration with gutters and roof penetrations ensures a weather-tight system. Additionally, using a quality synthetic underlayment beneath the metal panels enhances durability and energy efficiency.

Frequently Asked Questions (FAQs)

Can you install a metal roof directly over existing shingles?
Yes, metal roofing can be installed directly over asphalt shingles provided the roof deck is in good condition and there are no more than two layers of shingles. This approach saves time and reduces disposal costs.

What preparation is required before installing metal roofing over shingles?
Remove any damaged or loose shingles, inspect the roof decking for rot or damage, and ensure the surface is clean and dry. Installing a quality underlayment or a metal roofing panel underlayment is also recommended to improve moisture protection.

Do I need additional ventilation when installing metal roofing over shingles?
Proper ventilation is essential to prevent moisture buildup and extend the lifespan of both the metal roof and the underlying shingles. Installing ridge vents or soffit vents may be necessary depending on the existing ventilation system.

What type of fasteners should be used for metal roofing over shingles?
Use corrosion-resistant screws with rubber washers specifically designed for metal roofing. These fasteners ensure a secure attachment and help prevent leaks by creating a watertight seal.

Will installing metal roofing over shingles affect my roof’s warranty?
Some metal roofing manufacturers may void warranties if installed over existing shingles without proper preparation. It is important to review warranty terms and consult with the manufacturer before installation.

How does installing metal roofing over shingles impact roof height and aesthetics?
Installing metal roofing over shingles will raise the roof profile slightly, which may affect gutters, flashing, and overall appearance. Professional assessment is advised to address any adjustments needed for a clean, finished look.
Installing a metal roof over existing shingles is a practical and efficient way to upgrade your roofing system without the need for complete tear-off. The process involves thorough preparation, including inspecting the current roof for damage, ensuring the surface is clean and secure, and installing a proper underlayment to provide an additional moisture barrier. Proper fastening techniques and the use of appropriate flashing and trim are essential to ensure durability and weather resistance.

One of the key advantages of installing metal roofing over shingles is the reduction in labor and disposal costs, as well as minimizing disruption to the home. However, it is important to verify local building codes and manufacturer guidelines to confirm that overlay installation is permitted and to maintain warranty coverage. Attention to ventilation and insulation beneath the metal roof will also contribute to the system’s overall performance and energy efficiency.

In summary, a metal roof installed over shingles offers a long-lasting, low-maintenance solution that enhances curb appeal and protects the structure. By following best practices and ensuring proper installation techniques, homeowners can achieve a reliable and aesthetically pleasing roofing upgrade that stands the test of time.

Author Profile

Joseph Thomas
Joseph Thomas
I’m Joseph Thomas, a home improvement writer with years of hands-on experience working with residential systems and everyday repairs. Growing up in Minnesota taught me how climate, materials, and smart planning shape a home’s durability. Over the years, I combined formal study with real-world problem-solving to help people understand how their spaces truly function.

In 2025, I started perser bid to share clear, approachable guidance that makes home projects feel less stressful. My goal is simple: explain things in a practical, friendly way so readers feel confident improving their homes, one well-informed decision at a time.