Which value represents the minimum pitch for asphalt roof systems expressed as a fraction per 12 horizontal?

Which value represents the minimum pitch for asphalt roof systems expressed as a fraction per 12 horizontal?

• A. 3/12
• B. 2/12
• C. 4/12
• D. 5/12

Answer: (B)

The key idea is the slope needed for asphalt shingles to shed water properly and allow correct installation. For asphalt roof systems, the minimum pitch is 2/12, meaning the roof must rise 2 inches for every 12 inches of horizontal run (about a 1:6 ratio). This level provides enough drainage and workable space for fastening and sealing shingles. Pitches of 3/12, 4/12, or 5/12 are steeper and would still function, but they exceed the minimum, which is why 2/12 is the correct minimum value.

The key idea is the slope needed for asphalt shingles to shed water properly and allow correct installation. For asphalt roof systems, the minimum pitch is 2/12, meaning the roof must rise 2 inches for every 12 inches of horizontal run (about a 1:6 ratio). This level provides enough drainage and workable space for fastening and sealing shingles. Pitches of 3/12, 4/12, or 5/12 are steeper and would still function, but they exceed the minimum, which is why 2/12 is the correct minimum value.