What underlayment is required for asphalt shingles on roofs with slopes of 4:12 or greater?

What underlayment is required for asphalt shingles on roofs with slopes of 4:12 or greater?

• A. one layer #15 non-perforated felt
• B. one layer #15 perforated felt
• C. two layer #15 perforated felt
• D. two layer #15 non-perforated felt

Answer: (A)

For steep-slope roofs, the underlayment’s role is to provide a secondary moisture barrier while the shingles shed water quickly on the roof. When the slope is 4:12 or greater, one layer of 15-lb asphalt-saturated felt that is non-perforated is the standard requirement. The non-perforated material gives a continuous barrier against moisture; perforated felt would create openings that could let water pass through if moisture reaches the underlayment, and adding a second layer isn’t typically necessary at this slope. Two layers or perforated underlayment are generally reserved for lower slopes or special conditions, so the best choice is one layer of non-perforated 15-lb felt.

For steep-slope roofs, the underlayment’s role is to provide a secondary moisture barrier while the shingles shed water quickly on the roof. When the slope is 4:12 or greater, one layer of 15-lb asphalt-saturated felt that is non-perforated is the standard requirement. The non-perforated material gives a continuous barrier against moisture; perforated felt would create openings that could let water pass through if moisture reaches the underlayment, and adding a second layer isn’t typically necessary at this slope. Two layers or perforated underlayment are generally reserved for lower slopes or special conditions, so the best choice is one layer of non-perforated 15-lb felt.