Core TradesQuestion 151 of 700
On a roof slope of 4:12 or greater covered with asphalt shingles, the underlayment must consist of at least:
a.One layer, applied with specified horizontal and end laps
b.Two full layers regardless of slope
c.No underlayment when self-sealing shingles are used
d.A layer of rigid insulation board
Explanation
For slopes of 4:12 and steeper, a single layer of underlayment lapped a set amount at horizontal and end joints is required, because water sheds quickly. Slopes below 4:12 (down to the 2:12 minimum) require a doubled underlayment. Underlayment is never omitted, and rigid insulation is not underlayment.
Law Reference: 2025 CA Residential Code §R905.1.1Practice all 700 questions free — no signup required.
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