How Do You Install a Metal Roof Over Existing Shingles?
Installing a metal roof over existing shingles is an increasingly popular choice for homeowners looking to enhance their home’s durability and curb appeal without the hassle of a full roof tear-off. This approach offers a practical solution that can save both time and money, all while providing the long-lasting benefits of metal roofing. Whether you’re motivated by energy efficiency, weather resistance, or simply a fresh new look, understanding the basics of installing metal roofing over shingles is the first step toward a successful project.
This method involves layering a metal roof directly on top of the current shingle roof, which can simplify the installation process and reduce waste. However, it also requires careful preparation and consideration to ensure proper ventilation, secure attachment, and overall structural integrity. Homeowners and contractors alike must weigh the advantages against potential challenges, such as weight concerns and local building codes.
In the following sections, we’ll explore what you need to know before starting, including essential tools, materials, and best practices. Whether you’re a DIY enthusiast or planning to hire professionals, gaining a solid understanding of how to install a metal roof over shingles will help you make informed decisions and achieve a durable, attractive result.
Preparing the Roof Surface and Inspecting Shingles
Before installing a metal roof over existing shingles, it is essential to prepare the roof surface carefully. Begin by inspecting the shingles for any damage, rot, or loose areas. Damaged shingles must be repaired or replaced to provide a stable base for the metal panels. Additionally, remove any debris such as leaves, branches, or dirt that may interfere with the installation.
Check for any protruding nails or fasteners and hammer them down or remove them to avoid puncturing the metal panels later. It is also important to ensure that the roof deck beneath the shingles is in good condition. If the decking shows signs of water damage or structural weakness, address these issues before proceeding.
In some cases, it may be necessary to add a layer of underlayment over the shingles to provide an additional moisture barrier and improve the overall durability of the roof. Synthetic underlayments are often preferred due to their resistance to tearing and superior water resistance compared to traditional felt paper.
Installing Furring Strips or Purlins
To create a proper air gap and secure metal panels over shingles, installing furring strips or purlins is a common and recommended practice. These strips provide a level surface for attaching metal panels and improve ventilation, which helps to prevent condensation buildup under the metal roof.
Furring strips are typically made from pressure-treated wood or metal and are fastened perpendicular to the roof rafters or trusses. The spacing of the strips depends on the type of metal roofing and the required fastening pattern but generally falls between 16 to 24 inches on center.
Key considerations when installing furring strips include:
- Ensuring strips are straight and level to prevent uneven metal panel installation.
- Using corrosion-resistant fasteners to avoid rust stains and maintain longevity.
- Maintaining consistent spacing to align with metal panel ribs or fastening points.
Applying Underlayment and Flashing
After securing the furring strips, the next step is to apply an underlayment. This layer acts as a secondary water barrier and protects the roof deck if water penetrates the metal roofing. Roll out the underlayment horizontally starting from the bottom edge of the roof, overlapping each row by several inches according to manufacturer recommendations.
Flashing installation is critical to prevent water infiltration at roof penetrations, edges, and valleys. Common flashing types include drip edges, ridge caps, vent flashing, and step flashing around chimneys or skylights. Ensure that flashing is installed beneath the underlayment where appropriate and sealed tightly to create a waterproof barrier.
Mounting Metal Roofing Panels
With the preparatory steps complete, you can begin mounting the metal roofing panels. The choice of panel profile (standing seam, corrugated, ribbed) will influence the fastening method and layout. Panels are typically installed starting from the bottom edge of the roof and working upward to facilitate water runoff.
Fastening methods include screws with rubber washers designed specifically for metal roofs to prevent leaks. It is vital to use the correct length fasteners to penetrate through the metal, furring strips, and into the roof decking securely.
When overlapping panels, follow the manufacturer’s guidelines to ensure proper sealing and wind resistance. Seams should be tight, and any required sealants or closures applied to prevent water and air infiltration.
| Step | Purpose | Materials/Tools Needed |
|---|---|---|
| Inspect and Repair Shingles | Ensure stable base and remove debris | Hammer, replacement shingles, nails |
| Install Furring Strips | Create level surface and ventilation gap | Pressure-treated wood strips, corrosion-resistant screws, level |
| Apply Underlayment | Secondary moisture barrier | Synthetic underlayment roll, utility knife |
| Install Flashing | Prevent water infiltration at critical points | Metal flashing pieces, sealant, nails |
| Mount Metal Panels | Final roof covering installation | Metal roofing panels, screws with washers, drill |
Ventilation and Insulation Considerations
Proper ventilation is critical when installing a metal roof over shingles to prevent heat buildup and moisture accumulation. The air gap created by furring strips facilitates airflow beneath the metal panels, which can extend the roof’s lifespan and improve energy efficiency.
In addition to ventilation, consider adding insulation beneath the roof deck or inside the attic space to optimize thermal performance. Materials such as rigid foam boards or spray foam insulation can be used depending on the existing roof structure and climate requirements.
Safety Precautions and Best Practices
Working on a roof requires strict adherence to safety protocols. Use appropriate fall protection equipment such as harnesses and guardrails. Secure ladders properly and wear non-slip footwear.
Best practices include:
- Checking weather conditions before starting installation to avoid working on wet or icy surfaces.
- Using gloves and eye protection when handling metal panels and tools.
- Having a helper to assist with panel handling, especially for large or heavy pieces.
Following these guidelines will ensure a safe, efficient, and durable metal roof installation over existing shingles.
Preparing the Roof Surface for Metal Installation
Before installing a metal roof over existing shingles, thorough preparation of the roof surface is critical to ensure durability and proper function. Begin by inspecting the current shingle roof for any damage such as loose, curling, or missing shingles. Repair or replace compromised areas to create a stable base.
Next, clean the roof surface to remove debris, moss, or dirt that might interfere with the metal roofing installation. Use a broom or blower, and ensure gutters and downspouts are clear to facilitate proper drainage.
Evaluate the roof’s decking condition by accessing the attic or roof interior. The decking must be solid and free from rot or water damage. Replace any weakened sections to prevent structural issues once the metal panels are installed.
Finally, install a high-quality underlayment designed for metal roofing applications. Synthetic underlayments are preferred for their durability and moisture resistance. This layer acts as a moisture barrier and improves the roof system’s longevity.
- Inspect and repair existing shingles
- Clean roof surface thoroughly
- Assess and repair roof decking if needed
- Install synthetic roofing underlayment
Installing Furring Strips for Proper Ventilation and Fastening
Furring strips are essential when installing metal roofing over shingles, as they create a ventilation gap and provide a solid nailing surface for metal panels. Without this step, moisture can become trapped, leading to corrosion and reduced roof lifespan.
Use treated 1×3 or 1×4 wood strips, spaced evenly across the roof perpendicular to the rafters. Typically, furring strips are installed every 16 to 24 inches on center, but verify spacing based on your metal panel type and manufacturer recommendations.
Secure the strips directly over the existing shingles with corrosion-resistant screws long enough to penetrate the roof decking by at least 1 to 1.5 inches. Ensure strips are flush and level to avoid uneven metal panel installation.
| Step | Description | Recommended Materials |
|---|---|---|
| Measure and Mark | Mark lines perpendicular to rafters at 16-24 inch intervals | Chalk line, tape measure |
| Cut Furring Strips | Cut treated wood strips to match roof length | Treated 1×3 or 1×4 lumber |
| Fasten Strips | Screw strips through shingles into decking | Corrosion-resistant screws (3-inch recommended) |
Laying and Securing Metal Roofing Panels
Once the furring strips are in place, metal roofing panels can be installed. Start at the eave edge, aligning the first panel squarely with the roof edge. Metal panels typically overlap on the sides and ends to create a weather-tight seal.
Use manufacturer-recommended fasteners, usually self-drilling screws with neoprene washers, to secure panels to the furring strips. Place fasteners at every rib or panel flange depending on panel style, and follow specific spacing guidelines—commonly every 12 to 24 inches along each fastening line.
To prevent damage during installation, use soft-soled shoes and handle panels carefully. Overlap panels sufficiently to avoid water infiltration, and seal overlaps with metal roofing sealant if recommended.
- Align first panel at roof edge ensuring square placement
- Overlap panels side-to-side and end-to-end as per instructions
- Secure with self-drilling screws with neoprene washers
- Follow fastening pattern and spacing per manufacturer
- Seal overlaps and fastener penetrations if needed
Integrating Flashing and Roof Penetrations
Proper flashing installation is vital to maintain roof integrity and prevent leaks, especially when installing metal roofing over shingles. Flashing must be carefully installed around chimneys, vents, skylights, and valleys to channel water away from these vulnerable points.
Use metal-compatible flashing materials such as galvanized steel or aluminum. Install drip edges along eaves and rakes to direct water off the roof and protect underlying components. Flashing should be layered correctly, with underlayment and shingles below the flashing and metal panels overlapping the flashing.
For roof penetrations, install metal collars or boot flashings that snugly fit around pipes or vents. Secure these flashings to the furring strips and seal edges with roofing sealant to prevent moisture entry.
| Flashing Type | Purpose | Installation Notes |
|---|---|---|
| Drip Edge | Directs water off roof edges | Install beneath underlayment at eaves; over underlayment at rakes |
| Valley Flashing | Channels water where roof planes meet | Use open or closed metal valleys; seal edges carefully | Professional Insights on Installing Metal Roofs Over Shingles