CSLB General Building (B)Framing and CarpentryMedium
A residential stairway has a total horizontal run of 99 inches distributed evenly over 9 equal treads. Per the California Residential Code, what is the run (depth) of each tread, and does the stairway comply with the minimum tread run requirement?
- A11 inches per tread; does not comply because treads must be at least 12 inches
- B9 inches per tread; does not comply with the 10-inch minimum
- C11 inches per tread; complies, since it exceeds the 10-inch minimum
- D9.9 inches per tread; complies because the code minimum is 9 inches
Show answer & explanationAnswer & explanation
Correct answer: C. 11 inches per tread; complies, since it exceeds the 10-inch minimum
Dividing the total run of 99 inches by 9 treads gives 11 inches per tread (99 ÷ 9 = 11). The CRC requires a minimum tread run of 10 inches for residential stairs, so an 11-inch tread run complies with the code.
Why the other options are wrong
- A. 11 inches is correct but 12 inches is not the code minimum for standard residential stairs.
- B. Incorrect division; 99 divided by 9 is 11, not 9.
- D. Incorrect math and incorrect minimum value; the code minimum is 10 inches, not 9.
Minimum Tread Run
The California Residential Code requires a minimum tread run (depth) of 10 inches for residential stairways, measured horizontally.
- Tread run = total run ÷ number of treads
- Number of treads = number of risers minus 1
- 10-inch minimum applies to standard stairs (not spiral)
Memory trick: Divide total run by tread count to find each step's depth—compare to the 10-inch floor.