Best Underlayment for Metal Roof Over Shingles: Fast-Track Guide to Choosing the Right UnderlaymentSarah ThompsonSep 09, 2025Table of ContentsTips 1:FAQTable of ContentsTips 1FAQFree Smart Home PlannerAI-Powered smart home design software 2025Home Design for FreeChoosing the best underlayment for installing a metal roof over existing shingles is crucial for the overall durability, weatherproofing, and energy efficiency of your roofing system. The underlayment serves as an additional protective barrier against moisture, wind, and heat transfer. For most homeowners and contractors, the preferred options are synthetic underlayments and self-adhering membranes due to their superior resistance to water intrusion and tear strength compared to traditional felt paper. Synthetic underlayments, such as polypropylene or polyethylene products, offer high strength, longevity, and excellent moisture resistance, outperforming traditional asphalt-saturated felt. These materials remain stable under temperature fluctuations and are less prone to wrinkling or tearing during installation. For areas with heavy rain or ice dam risks, a self-adhering ice and water shield membrane (usually rubberized asphalt-based) is highly recommended, especially along eaves, valleys, and penetrations, offering additional leak-proofing. While synthetic underlayments work well for most climates, a designer’s perspective also focuses on proper ventilation and energy efficiency. When placing metal over existing shingles, it’s essential to ensure the assembly doesn’t trap heat or moisture, which might compromise the roof system or indoor comfort. Using an underlayment with a vapor barrier or integrated ventilation layers can help optimize both durability and performance. Interior designers often work closely with contractors to specify solutions that meet both aesthetic and technical requirements; for instance, a synthetic underlayment paired with a radiant barrier could improve indoor energy efficiency and comfort. For those planning a roof upgrade and wanting to visualize layout and structural impacts, utilizing a digital platform like a home designer tool enables detailed planning, material selection, and integration with the home’s overall aesthetic, which is essential from a design perspective.Tips 1:Always check local building codes and manufacturer warranties before choosing your underlayment. Some codes may restrict leaving old shingles in place or specify certain underlayment types for metal roofing. Consult with both your contractor and a designer to ensure compatibility and performance.FAQQ: Can I install a metal roof directly over shingles without underlayment?A: No. An underlayment is essential to prevent moisture infiltration and improve overall roof performance.Q: What is the main advantage of synthetic underlayment for metal roofs?A: Synthetic underlayments offer superior durability, moisture resistance, and longevity compared to felt paper.Q: Is an ice and water shield necessary with metal roofs?A: It’s highly recommended in colder climates or where leaks are a concern, particularly along eaves and valleys.Q: Will extra layers increase attic heat?A: Potentially, yes. Choosing the right underlayment with venting capability or radiant barrier can minimize heat retention.Q: How does underlayment affect roof warranty?A: Using a manufacturer-approved underlayment is often required to maintain the metal roofing warranty—always verify before installation.Home Design for FreePlease check with customer service before testing new feature.