Stair Layout and Construction
Stair Layout and Construction
This domain covers total rise, unit rise and run, treads, stringers, landings, and railings. The exam tests whether the stair is comfortable, code-compliant, and framed safely.
Core rules
- Measure total rise from finished floor to finished floor. Divide by a target riser, then adjust to equal risers within the code limit.
- The number of treads is one fewer than the number of risers when the top landing serves as the last tread.
- Unit run is the horizontal tread depth less any nosing; nosing projects beyond the riser but does not increase the walkable run.
- Stringers must be sized for the span and cut accurately; check headroom, handrail height, and guard requirements under the local code.
- Keep riser height and tread depth consistent; variation is a trip hazard.
Worked example
Total rise = 108 in. Try 15 risers: 108 ÷ 15 = 7.2 in per riser, within the common 7-3/4 in maximum. With 15 risers there are 14 treads. At a 10-in unit run, total run = 140 in. Check that this fits the available space and that headroom is adequate before cutting stringers.
Traps
Dividing by 14 instead of 15 when counting risers, measuring from subfloor to subfloor instead of finished surfaces, and adding the nosing to the unit run are common mistakes. Do not assume a staircase that fits is code-compliant.