How to Install Metal Roofing Over Shingles: A Comprehensive Guide

Are you tired of replacing your roof every 15-20 years? Did you know that a properly installed metal roof can last 50 years or more, often outliving the house it protects? Replacing an aging shingle roof can be a costly and disruptive project, but there’s a way to upgrade to the superior durability and longevity of metal without the hassle of a complete tear-off. Installing metal roofing directly over existing asphalt shingles is a viable option for many homeowners, offering significant savings on labor and disposal costs while providing a beautiful and durable roof for decades to come. However, it’s critical to understand the process and potential challenges to ensure a successful and long-lasting installation.

The advantages of this approach are numerous, from cost savings and reduced landfill waste to improved insulation and a more attractive home. Installing metal over shingles creates an additional layer of protection against the elements and can even increase your home’s resale value. But it’s not a decision to be taken lightly. Factors like the condition of your existing roof, local building codes, and proper installation techniques all play crucial roles in determining the feasibility and success of this project. Making informed decisions upfront will save you time, money, and potential headaches down the road.

What should I know before installing metal roofing over shingles?

How does the existing shingle layer impact fastener selection and spacing?

The existing shingle layer significantly impacts fastener selection and spacing when installing metal roofing because it adds thickness and compressibility to the roof deck. This necessitates longer fasteners to properly penetrate through the shingles and securely anchor into the underlying roof deck (typically plywood or OSB). Inadequate fastener length can lead to pull-out issues, particularly over time as the shingles compress and the metal roofing expands and contracts with temperature changes. Also, the inherent unevenness of shingles affects the contact between the metal panel and the deck, requiring more frequent fastener spacing to maintain a secure attachment and prevent panel flutter or damage in high winds.

When installing metal roofing over shingles, it is crucial to accurately determine the combined thickness of the shingle layer and any underlayment. This measurement will dictate the minimum fastener length required. Consult with the metal roofing manufacturer’s specifications and local building codes to ensure compliance. Selecting the correct fastener type is equally important. Self-drilling screws are often preferred as they can easily penetrate the shingle layer and the underlying sheathing, creating a secure and weatherproof connection. Consider using fasteners with rubber washers to further seal the penetration points and prevent water intrusion. Increasing the fastener density can compensate for the reduced holding power caused by the compressible shingle layer. While manufacturer specifications provide guidelines, adjusting fastener spacing may be necessary based on specific factors like wind exposure and the type of shingles present. For instance, a roof in a high-wind zone with multiple layers of thick asphalt shingles might require closer fastener spacing than a roof in a low-wind area with a single layer of thinner shingles. Remember, over-fastening is generally preferable to under-fastening in this scenario to ensure the long-term integrity and performance of the metal roof.

Will installing metal roofing over shingles affect ventilation?

Yes, installing metal roofing directly over existing shingles can significantly reduce or completely block your roof’s existing ventilation, potentially leading to moisture buildup, premature deterioration of the roof deck, and decreased energy efficiency.

Proper roof ventilation is crucial for maintaining a healthy and long-lasting roof system. When you cover shingles with metal without creating an airspace, you trap moisture that rises from inside the house. This trapped moisture can condense on the underside of the metal roofing, leading to mold growth, wood rot in the roof decking, and compromised insulation. Furthermore, lack of ventilation can cause the metal roof to heat up excessively in the summer, transferring that heat into your home and increasing cooling costs. To avoid these issues, it’s vital to create a ventilation system when installing metal over shingles. This typically involves installing furring strips or a similar framework to create an airspace between the shingles and the metal roofing. These strips are installed vertically allowing air to enter at the eaves (soffit vents) and exit at the ridge (ridge vent). This airflow helps to remove moisture and regulate the temperature of the roof, ensuring its longevity and performance. The alternative is to remove the shingles entirely before installing the metal roof. The choice between installing a ventilated metal roof over shingles or removing the shingles altogether depends on the condition of the existing shingles and your budget. If the shingles are in good condition, installing a ventilated system can be a cost-effective option. However, if the shingles are deteriorated, removing them is generally recommended to ensure a solid base for the new metal roof and to avoid any potential issues with trapped moisture and rot. Consulting with a qualified roofing contractor is crucial to determine the best approach for your specific situation.

How do I properly flash around chimneys and other penetrations over shingles?

Proper flashing around chimneys and other penetrations when installing metal roofing over shingles is crucial for a watertight seal. This involves creating a system that integrates the metal roofing with the existing shingles, the penetration itself, and the flashing materials, allowing water to flow smoothly down the roof without seeping underneath.

The process typically begins with removing shingles immediately surrounding the penetration to expose a clean surface. Install a continuous piece of metal flashing (apron flashing) at the base of the chimney or penetration, overlapping the shingles below and extending a few inches up the chimney. Step flashing is then interwoven with the shingles and the sides of the chimney, bending each piece to direct water away from the penetration. For the top of the chimney, create a saddle flashing that diverts water around the back. Each piece of flashing should overlap the one below it, creating a shingle-like effect that channels water downwards.

It is also crucial to properly seal all flashing seams and edges using a high-quality sealant specifically designed for roofing applications. Consider using counter-flashing embedded into the chimney’s mortar joints for superior protection; this helps to prevent water from penetrating behind the flashing system. Remember that the existing shingles will affect how high you need to flash. Ensure you consider the height of the shingle profile to ensure appropriate overlap is achieved.

What are the fire safety considerations of installing metal roofing over shingles?

Installing metal roofing over existing asphalt shingles generally improves a roof’s fire resistance, as metal is a non-combustible material. However, potential fire safety concerns exist, primarily related to the creation of a concealed space between the metal and shingle layers, which could allow for the undetected spread of fire or embers. Ensuring proper ventilation and using fire-resistant underlayment are crucial for mitigating these risks.

The key fire safety advantage of metal roofing is its inherent non-combustibility. Unlike asphalt shingles, metal will not ignite or contribute to the spread of flames. This provides a significant barrier against external fires, such as wildfires or those originating from neighboring structures. However, the space between the existing shingle layer and the new metal roof can act as a pathway for embers or flames to travel, potentially igniting the shingles from beneath. This concealed space makes it harder to detect and extinguish such fires quickly, increasing the risk of more significant damage. To address these concerns, consider installing a fire-resistant underlayment between the shingles and the metal roofing. This layer adds an extra level of protection and can help prevent flames from spreading through the concealed space. Furthermore, proper ventilation is critical. Ensuring adequate airflow under the metal roof will help dissipate heat and moisture, which can contribute to the deterioration of the shingles and increase the risk of fire. Follow local building codes and manufacturer’s guidelines to ensure proper installation techniques that minimize potential fire hazards.

Does installing metal over shingles void any warranties (shingle or metal)?

Yes, installing metal roofing directly over existing asphalt shingles *can* void both the shingle manufacturer’s warranty and, potentially, the metal roofing warranty. However, the specifics depend entirely on the warranty terms of each product and local building codes.

Often, shingle warranties are voided because the underlying shingles contribute to premature metal roof failure due to trapped moisture, excessive heat buildup, or uneven surfaces. Shingle manufacturers design their products to be installed over a prepared roof deck, not to serve as an underlayment. Covering them essentially prevents proper ventilation and can accelerate shingle deterioration, leading to warping, buckling, and other problems that negatively impact the metal roof’s performance. Check your specific shingle warranty for clauses regarding modifications or covering of the shingles. Metal roofing warranties may also be affected if the installation doesn’t conform to the manufacturer’s specifications. These specifications frequently require a specific underlayment and ventilation system that direct installation over shingles inherently violates. Even if the metal roofing material itself carries a warranty, improper installation due to underlying shingle issues could lead to a claim denial. Always consult with the metal roofing manufacturer and a qualified installer to determine the proper installation method and whether it will affect the warranty. Ignoring these considerations might lead to a costly repair or replacement down the road with no warranty coverage.

Alright, you’ve made it! Hopefully, you’re now feeling confident and ready to tackle that metal roofing project. Remember to take your time, double-check your measurements, and stay safe up there! Thanks for reading, and we hope this guide has been helpful. Come back and visit us again soon for more DIY tips and tricks!