What is the minimum slope on which asphalt strip shingles may be installed?

What is the minimum slope on which asphalt strip shingles may be installed?

• A. 3:12
• B. 1:12
• C. 4:12
• D. 2:12

Answer: (D)

The minimum slope for installing standard asphalt strip shingles is two inches of vertical rise for every twelve inches of horizontal run. This two-to-twelve (2:12) ratio lets water shed properly and gives enough surface for the shingle tabs to seal as they heat in the sun. If the roof is flatter than this, shingles may not seal correctly and leaks can occur, so a different roofing approach or extra underlayment per manufacturer guidelines is needed. Steeper slopes (like three or four inches per foot) meet or exceed the minimum and are acceptable, but the key point is that two inches per foot is the minimum.

The minimum slope for installing standard asphalt strip shingles is two inches of vertical rise for every twelve inches of horizontal run. This two-to-twelve (2:12) ratio lets water shed properly and gives enough surface for the shingle tabs to seal as they heat in the sun. If the roof is flatter than this, shingles may not seal correctly and leaks can occur, so a different roofing approach or extra underlayment per manufacturer guidelines is needed. Steeper slopes (like three or four inches per foot) meet or exceed the minimum and are acceptable, but the key point is that two inches per foot is the minimum.