Built-up roofs should be installed on roof slopes 0.25:12 or greater (2015 IRC R905.9.1), except for coal-tar built-up roofs that have a minimum roof slope of one-eighth unit vertical in 12 units horizontal (1% slope).
Wood shakes should be installed on roof slopes 3:12 or greater (2015 IRC R905.8.2).Wood shingles should be installed on roof slopes 3:12 or greater (2015 IRC R905.7.2).Slate shingles should be installed on roof slopes 4:12 or greater (2015 IRC R905.6.2).Mineral-surfaced roll roofing should be installed on roof slopes 1:12 or greater (2015 IRC R905.4.2).Metal roof shingles should be installed on roof slopes 3:12 or greater (2015 IRC R905.4.2).Clay and concrete roof tiles should be installed on roof slopes 2.5:12 or greater (2015 IRC R905.3.2).Asphalt shingles should be installed on roof slopes 2:12 or greater (2015 IRC R905.2.2).
