CSLB General Building (B)Framing and CarpentryHard
A stairway has a total vertical rise of 108 inches from the lower finished floor to the upper finished floor. Using the CRC maximum riser height of 7 3/4 inches, what is the minimum number of risers required, and what is the resulting actual riser height when the rise is divided evenly?
- A14 risers at 7.75 inches each
- B14 risers at 7.71 inches each
- C15 risers at 7.20 inches each
- D13 risers at 8.31 inches each
Show answer & explanationAnswer & explanation
Correct answer: B. 14 risers at 7.71 inches each
Dividing 108 inches by the maximum 7.75-inch riser gives 13.94, which must be rounded up to 14 risers (you cannot use a fractional riser and cannot exceed the max height). Dividing 108 by 14 gives an actual riser height of 7.71 inches, which meets the code maximum and keeps all risers uniform.
Why the other options are wrong
- A. 14 risers at exactly 7.75 inches would total 108.5 inches, not matching the actual 108-inch rise.
- C. 15 risers is more than the minimum required and produces unnecessarily short risers.
- D. 13 risers would require an 8.31-inch riser height, which exceeds the 7.75-inch maximum.
Riser Calculation from Total Rise
To find the number of risers, divide total rise by the maximum allowed riser height and round up to the next whole number, then divide total rise by that number of risers to get the actual uniform riser height.
- Formula: risers = ceiling(total rise ÷ max riser height)
- Actual riser height = total rise ÷ number of risers
- All risers in a flight must be within 3/8 inch of each other
Memory trick: 'Round up the risers, then split the rise fair.'