CSLB General Building (B)Finishes and Building EnvelopeEasy
A contractor is installing standard three-tab composition (asphalt) shingles on a garage addition. Per the California Residential Code, what is the minimum roof slope allowed for shingle application using a single layer of underlayment?
- A4:12
- B1:12
- C2:12
- D6:12
Show answer & explanationAnswer & explanation
Correct answer: C. 2:12
The CRC requires a minimum slope of 2:12 for composition shingles; slopes between 2:12 and 4:12 require double underlayment, and below 2:12 shingles are not permitted at all.
Why the other options are wrong
- A. This is the minimum slope for single-layer underlayment, not the absolute minimum.
- B. Too flat; shingles are not approved below 2:12.
- D. A common slope but far above the code minimum.
Minimum Shingle Slope
The CRC sets 2:12 as the lowest roof pitch on which composition shingles may be installed, provided special underlayment rules are followed.
- 2:12–4:12 requires double underlayment
- Below 2:12: use low-slope roofing (e.g., membrane) instead
- Steeper than 4:12 allows single-layer underlayment
Memory trick: 'Two by twelve, shingles just squeak by.'