Some standard roofing materials, such as metal and shingles, are unsuitable for roofs with a low pitch, or slope. Roll roofing, or rolled roofing, material is a common solution to this problem on low-sloped roofs that do not require great structural strength, such as those of garages, porches and sheds.
The minimum slope requirement for mineral-covered roll roofing material is half an inch per foot (4 percent). Organic roll roofing can be installed on roofs with a minimum slope of 1 inch and, while asphalt roll roofing can be installed on a 2-inch slope in an emergency, a minimum slope of 3 inches is recommended.
Roll roofing is typically applied to a roof in strips 3 feet wide, with one sheet overlapping the next to provide double coverage across the entire roof surface. It is usually applied over a layer of tar paper.
Roll roofing can be installed vertically or horizontally, but vertical installation creates long seams that may allow rainwater to penetrate the roof. Roll roofing is not particularly appealing, aesthetically, and is best installed on roofs that are not overlooked.