Minimum Slope
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.
Application
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.
Considerations
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.