Roll roofing: pick the right roll, lay it right

Roll roofing is roofing sold in rolls instead of shingles or panels. The classic kind is mineral surface roll roofing: asphalt on a mat with a granule face, about 36 inches wide. The word also covers peel-and-stick modified bitumen, EPDM rubber and TPO membranes, and the felt and synthetic underlayment that go under a roof.

A standard mineral surface roll covers about one square, which is 100 square feet, after laps. GAF says one roll of its Mineral Guard covers 100 square feet. A 19 inch selvage roll covers about half a square because each course overlaps the last by 19 inches.

The model residential code does not allow mineral surface roll roofing below 1 inch of rise per foot. Many makers set a higher limit: GAF and TAMKO instructions for their standard rolls say at least 2 inches per foot. Below that, use a low slope product such as peel-and-stick modified bitumen or EPDM.

Mineral surface roll roofing is the short-lived option. Published estimates run from about 5 to 15 years, depending on the product, the slope and the climate. Modified bitumen and EPDM membranes are generally estimated to last much longer. Treat any number as a rough estimate, not a promise.

Mineral surface roll roofing and peel-and-stick cap sheets are common do-it-yourself jobs on sheds, garages and porch roofs. The work is simple but the roof is not: secure your ladder, stay off wet roofs, use fall protection, and check your local code and the maker’s slope limits first.