Thinking about a roof upgrade? Did you know that installing metal roofing over existing asphalt shingles is a cost-effective and increasingly popular choice? Many homeowners are drawn to the long-lasting durability, energy efficiency, and enhanced aesthetic appeal that metal roofing provides. It’s a smart way to improve your home’s protection from the elements while potentially increasing its resale value.
Installing metal roofing directly over shingles can save you the labor and expense of removing the old roof, making it an attractive DIY project. However, it’s crucial to understand the proper techniques and potential pitfalls involved. A poorly executed installation can lead to problems like trapped moisture, reduced lifespan of your new roof, or even structural damage. Following best practices is essential for a successful and long-lasting metal roof.
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Do I need to install furring strips before the metal roofing?
Whether you need to install furring strips (also called battens) before installing metal roofing over shingles depends primarily on your local building codes, the condition of the existing shingles, and the type of metal roofing you’re planning to install. In many cases, it’s highly recommended, and sometimes required, to install furring strips.
Furring strips create an air gap between the metal roofing and the shingles. This ventilation is crucial for preventing condensation build-up, which can lead to rust, mold growth, and premature failure of both the metal roofing and the underlying shingles. Without proper ventilation, moisture can become trapped, accelerating corrosion and potentially damaging the roof deck. Furring strips also provide a level surface for attaching the metal roofing, especially if the existing shingles are uneven or damaged. This ensures a more uniform and aesthetically pleasing appearance. Furthermore, consider the type of metal roofing you’re using. Standing seam metal roofs often perform better with furring strips as they provide a solid and consistent attachment point, minimizing the risk of buckling or oil-canning (a wavy appearance). Exposed fastener metal roofs might seem simpler to install directly over shingles, but the lack of ventilation can still cause problems. Check with the metal roofing manufacturer’s installation guidelines and local building codes to determine the best approach. Ignoring these guidelines can void warranties and lead to costly repairs down the line. Ultimately, installing furring strips is a proactive step that can significantly extend the lifespan of your metal roof and protect your investment.
What type of underlayment is best over existing shingles?
The best type of underlayment to install over existing asphalt shingles before installing metal roofing is a high-temperature self-adhered underlayment. This type of underlayment provides a crucial thermal barrier and waterproofing layer, protecting the metal from reacting with the asphalt, and preventing moisture issues that can arise from condensation.
High-temperature self-adhered underlayments are specifically designed to withstand the elevated temperatures that metal roofs can reach, especially in sunny climates. Standard underlayments may degrade or melt under these conditions, compromising their effectiveness. The self-adhering quality ensures a tight, waterproof seal over the shingle surface, minimizing the risk of water infiltration that can lead to rot and mold growth. Furthermore, it creates a smoother surface for the metal roofing, reducing the chances of imperfections in the shingle surface telegraphing through to the new metal roof. When selecting a high-temperature self-adhered underlayment, it’s essential to check the manufacturer’s specifications to ensure it’s compatible with both asphalt shingles and the chosen metal roofing material. Some underlayments are specifically formulated for certain metal types, such as steel or aluminum. Proper installation, including adequate overlap and sealing around penetrations, is critical to maximize the underlayment’s protective properties. Ignoring proper installation can lead to premature failure of the underlayment and compromise the performance of the entire roofing system.
How do I deal with unevenness in the existing shingle roof?
Unevenness in an existing shingle roof is a common challenge when installing metal roofing over it and requires careful consideration to prevent issues like oil-canning (a wavy appearance) and compromised weather tightness. The primary solution involves creating a smooth, consistent substrate upon which to install the metal panels. This typically means addressing dips, humps, and loose or missing shingles.
The best approach depends on the severity of the unevenness. For minor imperfections, a layer of underlayment, like a high-temperature ice and water shield or a synthetic underlayment, might suffice. The underlayment acts as a cushion, smoothing out slight variations and providing a moisture barrier. For more significant unevenness, you may need to install a layer of strapping or furring strips over the existing shingles. These strips, typically made of wood, are fastened to the roof deck and provide a level surface for the metal roofing. Shimming behind the furring strips can correct for more pronounced dips or humps. Before installing any new materials, thoroughly inspect the existing shingle roof. Identify and address any underlying structural issues, such as sagging rafters or rotted sheathing. Failing to do so will compromise the integrity of the entire roofing system, regardless of how level the surface appears. Consider a professional inspection to help identify any hidden problems. When installing furring strips, ensure they are properly spaced according to the metal roofing manufacturer’s specifications to maintain proper panel support and avoid deflection. Remember that adding layers increases the overall weight on the roof structure, so verify that the framing can handle the additional load before proceeding.
Will the added weight of metal roofing damage my roof structure?
Generally, no, the added weight of metal roofing installed over existing asphalt shingles is unlikely to damage your roof structure if your roof is currently sound and built to code. Most metal roofing systems are surprisingly lightweight, often weighing less than or comparable to a second layer of asphalt shingles.
The critical factor is the existing condition of your roof. Before installing any new roofing material, have a professional inspect your roof decking and support structure for signs of rot, water damage, or structural weakness. Addressing any pre-existing issues is paramount. If your roof is already sagging or showing signs of failure, adding any weight, even relatively light metal roofing, could exacerbate the problem. Local building codes also dictate load-bearing requirements for roofs. Ensure your roof meets those standards before proceeding. The type of metal roofing you choose also impacts the total weight. Standing seam metal roofing is typically lighter than metal shingles. Consider the gauge (thickness) of the metal; a higher gauge indicates a thinner and lighter material. Your contractor should be able to calculate the total weight per square foot of the chosen metal roofing and compare it to the existing load capacity of your roof. Remember to factor in snow load for your geographic area as well.
What screw length is appropriate for fastening the metal to the roof?
The appropriate screw length for fastening metal roofing over shingles is determined by adding the thickness of the metal panel, the thickness of the shingle layers (including any existing shingles and underlayment), and the desired depth of screw penetration into the roof decking. A general rule of thumb is to aim for at least 1 1/2 inches of screw penetration into the solid wood decking, although local building codes should always be consulted and take precedence.
When calculating the necessary screw length, it’s crucial to accurately assess the thickness of the existing shingle layers. Multiple layers of shingles can significantly increase the overall thickness that the screw must penetrate before reaching the roof deck. Measure the thickness in several areas to account for variations. Also, consider any underlayment materials used between the metal panels and the shingles, adding that thickness to the calculation. Using a screw that is too short will result in a weak connection, making the roof vulnerable to wind uplift and leaks. Conversely, using screws that are excessively long can also create problems. Overly long screws can protrude through the underside of the roof deck, posing a safety hazard and potentially interfering with electrical wiring or plumbing. Furthermore, excessively long screws can bend or mushroom when tightened, compromising the seal of the screw head against the metal panel. Therefore, precise measurement and calculation are essential for selecting the correct screw length for a secure and weatherproof installation. Always err on the side of caution and consult with a roofing professional or local building inspector if you are unsure about the proper screw length for your specific situation.
How do I properly flash around chimneys and vents?
Proper flashing around chimneys and vents when installing metal roofing over shingles is crucial to prevent leaks. This generally involves using a combination of step flashing, counter flashing (for chimneys), and specialized vent pipe flashings, all carefully integrated with the metal roof panels to ensure water is directed away from the penetration and down the roof.
The process starts with removing any existing flashing around the chimney or vent. For chimneys, install step flashing along the sides, weaving each piece between the shingles and the chimney. Each piece of step flashing should be bent at a 90-degree angle, with one side against the chimney and the other extending onto the roof. Apply a sealant beneath the step flashing and over the top edge that is against the chimney to prevent water intrusion. Once the metal roofing is installed, counter flashing is installed over the step flashing, embedded into the chimney’s mortar joints, and sealed. For vent pipes, use a pre-fabricated metal flashing with a rubber boot that fits snugly around the pipe. Slide the flashing over the pipe and carefully integrate it with the metal roofing, ensuring the upper edge is properly lapped by the overlapping metal panel above it. When installing the metal roofing panels, carefully cut around the flashed areas, leaving enough room for expansion and contraction. Ensure the metal panels overlap the flashing properly to create a watertight seal. Pay close attention to the top of the chimney or vent flashing. Water running down the roof has the most potential to enter at this point. Consider using a bead of sealant on top of the flashing as a final measure. Remember, precise cuts and careful attention to detail are vital for a leak-free and long-lasting roof.
What are the building code requirements for metal roofing over shingles in my area?
Building codes regarding metal roofing over existing shingles vary significantly depending on your specific location, primarily dictated by local municipal and county regulations. Generally, you will need to consult with your local building department to determine specific requirements related to weight limits, fastening methods, underlayment needs, fire ratings, and the permissibility of the installation itself. Ignoring these requirements can lead to fines, required removal, and insurance complications.
Before commencing any installation, a permit is almost always required. The permitting process involves submitting plans detailing the proposed installation, including the type of metal roofing, the fastening system, and how the existing shingles will be addressed. The building department will review these plans to ensure they meet local codes for wind resistance, snow load capacity, and fire safety. They may also require an inspection during and after the installation to confirm compliance. It’s crucial to understand that some jurisdictions may prohibit installing metal roofing directly over existing shingles altogether. This is often due to concerns about excessive weight on the roof structure, potential moisture buildup between the layers leading to rot, and the difficulty of properly inspecting the underlying roof deck for damage. In such cases, complete removal of the existing shingles may be mandated before installing the new metal roof. Always verify the specifics with your local authorities before proceeding.
And that’s it! You’ve successfully installed your new metal roof over those old shingles. Hopefully, this guide has helped make the process a little less daunting. We know it’s a big project, but with a little patience and the right tools, you can definitely handle it. Thanks for reading, and be sure to check back soon for more DIY tips and tricks!