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Roofing Tip: Preventing Ice Dams
The National Roofing Contractors Association recommends using a self-adhering polymer-modified bitumen sheet underlayment in areas where ice-dam protection is required.
An ice-dam protection membrane should extend from an eave’s edge to a point 24” inside the interior face of a building’s exterior wall; if a roof’s slope is less than 18 degrees, the ice-dam protection membrane should extend 36” beyond the exterior wall.
When choosing a specific product, check the product labels or specification sheets to verify a material is labeled as complying with ASTM D970, the standard for self-adhering sheet materials.
One word of caution: although most self-adhering polymer-modified bitumen sheet products are appropriate for use under asphalt shingles, wood shakes and wood shingles, the same product can get hot under sunlight during the summer when covered with metal panels, metal shingles, concrete or clay tiles. Most manufacturers offer a high-temperature product, as well as products that do not have mineral surfaces, which may abradethe underside of metal shingles.
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