Planning & EstimatingCâu 602 / 700
A common rafter has a horizontal run of 15 ft on a roof with a 5-in-12 slope (5 inches of rise per 12 inches of run). Ignoring overhang, what is the APPROXIMATE rafter length from ridge to top plate?
a.15 ft
b.16.25 ft
c.21.25 ft
d.19.5 ft
Giải thích
Rise = 15 x (5 / 12) = 6.25 ft. Rafter length = sqrt(run^2 + rise^2) = sqrt(15^2 + 6.25^2) = sqrt(225 + 39.06) = sqrt(264.06) = 16.25 ft (b). (This is a 5-12-13 triangle: 15 / 12 x 13 = 16.25.) Option (a) is the run only. Option (c) adds run and rise instead of using the hypotenuse. Option (d) overestimates the slope factor.
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