Framing & StructuralQuestion 378 of 700
A gable roof has a total run of 12 feet (horizontal from wall to ridge) and a slope of 6:12. Ignoring ridge and overhang, what is the approximate line length of a common rafter along the slope?
a.About 13 feet 5 inches
b.About 12 feet 0 inches
c.About 15 feet 0 inches
d.About 6 feet 0 inches
Explanation
Rafter line length equals run times the unit-length factor. For a 6:12 slope the diagonal per 12 units of run is the square root of (12² + 6²) = 13.416 units, a factor of about 1.118. Multiply 12 ft run by 1.118 to get roughly 13.42 ft, or about 13 ft 5 in. 12 ft ignores the slope; 15 ft overshoots; 6 ft is the rise, not the rafter length.
Law Reference: 2025 CA Residential Code §R802Practice all 700 questions free — no signup required.
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