Chapter 1 of 522% of exam

Planning and Estimating

Planning decides whether a roof is legal before any material is ordered; estimating turns plan dimensions into squares, rolls, bundles and hours. CSLB weights this section at 22% of the C-39 examination. For worked examples, named traps and a full practice exam at CSLB's weights, see the PrepPass C-39 Roofing study guide.

Choose the system the slope allows

Every roof covering has a minimum slope in the California Residential and Building Codes. Membrane systems drain at 1/4 inch per foot; units that shed water by overlapping need real slope. Check slope before fire class, wind rating or energy rules.

Membrane roofs
Built-up, modified bitumen, single-ply, spray foam and liquid-applied roofs need at least 1/4:12 for drainage; coal-tar built-up may be 1/8:12.
2025 CRC R905.9–R905.14
Shingles and tile
Asphalt shingles need 2:12 and clay or concrete tile 2-1/2:12, each with double underlayment up to 4:12.
2025 CRC R905.2.2, R905.3.2
Slate and wood
Slate needs 4:12; wood shingles, wood shakes and metal roof shingles need 3:12.
2025 CRC R905.4.2, R905.6.2, R905.7.2, R905.8.2

Fire, wind and energy on a reroof

Outside fire hazard zones, replacing more than half a roof in a year brings the whole roof to at least Class C; inside them, roofing is Class A. Shingles carry a wind class on the label. Large residential and nonresidential reroofs can trigger Energy Code cool-roof rules by climate zone.

Class C reroof trigger
More than 50 percent of the roof replaced within one year: the entire covering must be at least Class C.
2025 CRC R902.1.2
Fire zones
Roofs in Fire Hazard Severity Zones or the WUI need a Class A assembly.
2025 CWUIC 504.2
Nonresidential energy trigger
Alterations of more than 50 percent of the roof or 2,000 sq ft, whichever is less.
2025 Energy Code 141.0(b)2B

Estimating basics

A square is 100 sq ft. True roof area is plan area, overhangs included, times the slope factor. Lapped materials cover less than their length, and slope changes how much underlayment a roof needs.

Slope factor
Square root of (144 + rise squared), divided by 12; 6:12 is about 1.118.
Roofing math
Drip edge laps
Adjacent pieces overlap at least 2 inches.
2025 CRC R905.2.8.5
Attic ventilation
Net free area of 1/150 of the vented space, or 1/300 when the code's conditions are met.
2025 CRC R806.2

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