CSLB C-39 Roofing (Trade Exam) — All Questions
The figures these questions turn on, laid out by section on dense colour pages you can print: CSLB C-39 Roofing cheat sheet PDF — $9.99 →
55 questions
A 1,200 sq ft attic uses the 1/300 ratio, and half the area goes at the ridge. A ridge vent offers 18 sq in of net free area per foot. What length is needed?
- a.24 ft
- b.32 ft
- c.16 ft✓
- d.8 ft
Total required is 4 sq ft or 576 sq in, half is 288 sq in, and 288 divided by 18 is 16 ft. 32 ft uses the whole 576 sq in, 8 ft takes only a quarter of it, and 24 ft assumes a 12 sq in per foot product.2025 CRC R806.2
Three roof planes have plan areas of 900 sq ft at 4:12, 450 sq ft at 6:12 and 300 sq ft at 9:12. About how many squares of surface?
- a.18.3 squares✓
- b.16.5 squares
- c.18.8 squares
- d.20.6 squares
Each plane is multiplied by its own slope factor (about 1.054, 1.118 and 1.250), giving about 1,827 sq ft or 18.3 squares. 16.5 squares uses plan area alone, 20.6 applies the steepest factor to everything, and 18.8 averages the three factors without weighting by area.Roofing math
A single 20.5 ft valley is lined with 10-ft pieces of flashing, each end lap 4 inches. How many pieces are needed?
- a.3 pieces✓
- b.2 pieces
- c.4 pieces
- d.5 pieces
The first piece covers 10 ft and each added piece adds 9 ft 8 in after the 4-inch end lap, so two pieces reach 19 ft 8 in, which is short of 20.5 ft, and three reach 29 ft 4 in. Two pieces leave the valley uncovered, and four or five add whole pieces the length does not call for.2025 CRC R905.3.9
A hip roof face is a trapezoid with a 36-ft eave, a 16-ft ridge side and a 12-ft slant height. What is its area?
- a.312 sq ft✓
- b.192 sq ft
- c.624 sq ft
- d.432 sq ft
Trapezoid area is the average of the parallel sides times the height, (36 + 16)/2 x 12 = 312 sq ft. 432 uses the eave length alone, 192 uses the ridge side alone, and 624 forgets to halve the sum.Roofing math
A roofer holds a level 48 inches out horizontally from the roof surface and measures 16 inches of rise to the roof. What is the slope?
- a.4:12✓
- b.5:12
- c.16:12
- d.3:12
16 inches of rise over 48 inches of run is the same as 4 inches over 12. 3:12 would show 12 inches of rise, 5:12 would show 20 inches, and 16:12 reports the measured rise without scaling the run to 12.2025 CRC slope notation