Guidelines for asphalt shingle roofing
Roof slopes between 2:12 and 4:12 can use shingles, but require roof application techniques to take into account a greater potential for ice dam water backup. Roof slopes between 2:12 and 4:12 require a double underlayment application in accordance with Section R905.2.7. Slopes of 4:12 and above can use standard asphalt roofing