Torch-down roofing is a popular low-slope roofing method where modified bitumen sheets are applied using a torch to melt the bitumen, creating a secure, waterproof seal. However, blistering can occur when air or moisture becomes trapped beneath the membrane, causing bubbles or raised areas. This typically happens due to improper installation, such as insufficient heating or poor adhesion, or because of moisture trapped in the substrate or air pockets formed during application. Exposure to extreme temperature changes can also cause the bitumen to expand and contract, leading to blisters over time. While small blisters might not be immediately harmful, if left unchecked they can compromise the roof’s waterproof integrity and eventually lead to leaks or further damage.
To diagnose blistering yourself, start with a simple visual inspection, looking for raised, bubble-like spots or areas where the membrane looks uneven. Gently press on blisters; if they are soft or squishy, it often indicates trapped moisture. Avoid puncturing or tampering with blisters, as this can make the problem worse. Safe DIY checks include ensuring gutters and drainage are clear to prevent water pooling, which can exacerbate blistering. If you find multiple blisters, or if they are large and hard, it’s best to call a professional. When consulting a roofer, ask how they plan to address moisture issues before repairs and inquire whether the fix includes checking the roof’s underlying layers for damage. Also, clarify how the repair will affect your roof’s warranty, as some patches can void coverage if not done by certified professionals.