Which of the following is NOT an accepted expression of the minimum slope for asphalt shingles?

• A. 1/4
• B. 1/3
• C. 4/12
• D. 2/6

Answer: (A)

The minimum slope for asphalt shingles is expressed as rise over run, and the standard requirement is at least 4 inches of rise for every 12 inches of run. That is written as 4/12, which simplifies to 1/3 or can be shown as 2/6—both equivalent expressions of the same slope. An expression like 1/4 corresponds to 3 inches of rise per 12 inches of run, which is shallower than the required minimum and therefore not an accepted expression. So the expression that isn’t accepted is 1/4.