AI-generated answer
Metal shingle and shingle panel roof systems are often light enough to be installed over existing roof systems, including asphalt shingles. This can eliminate or defer the removal and disposal of old roofing materials, which is beneficial for sustainability and cost savings. For example, some metal roof systems have a durable, watertight design with side-lock systems that allow for quick installation over existing asphalt shingles while accommodating thermal expansion and contraction.
When installing metal over shingles, it is important to use appropriate underlayment and slip sheets to protect the roof deck and accommodate metal movement. The underlayment acts as a secondary water barrier, and a slip sheet prevents metal from sticking to the underlayment due to expansion and contraction. Proper fastening methods and fastener compatibility with the metal type are also critical to prevent corrosion and ensure long-term performance.
This approach is particularly advantageous for building owners with existing structures that cannot support the weight of heavier roofing materials like slate or concrete tiles, as metal roofing typically weighs between 100 and 200 pounds per square, much lighter than traditional tile or slate roofs.
