According to code, asphalt shingles installed on roof with a slope of 4:12 or greater require an underlayment of:

According to code, asphalt shingles installed on roof with a slope of 4:12 or greater require an underlayment of:

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

Answer: (B)

Underlayment acts as a secondary moisture barrier beneath asphalt shingles. For roofs with a slope of 4:12 or greater, the code calls for a single layer of asphalt-saturated felt, weight #15, that is non-perforated. The non-perforated type provides a watertight barrier under normal conditions, while perforated felt would allow moisture through and isn’t acceptable under shingles. Installing two layers isn’t required at this slope and would add unnecessary cost. So the correct choice is a single layer of non-perforated #15 felt.

Underlayment acts as a secondary moisture barrier beneath asphalt shingles. For roofs with a slope of 4:12 or greater, the code calls for a single layer of asphalt-saturated felt, weight #15, that is non-perforated. The non-perforated type provides a watertight barrier under normal conditions, while perforated felt would allow moisture through and isn’t acceptable under shingles. Installing two layers isn’t required at this slope and would add unnecessary cost. So the correct choice is a single layer of non-perforated #15 felt.