Understanding Stair Components
The tread is the horizontal foot surface, while the riser is the vertical face between treads. The stringer is the inclined structural member supporting treads and risers. The handrail provides user support, while balusters form the vertical infill. Newel posts anchor the handrail system at stair start, end, and turns.
Building Code Requirements
The International Residential Code specifies maximum riser height of 7.75 inches and minimum tread depth of 10 inches. The sum of one riser and tread should fall between 17 and 18 inches for comfortable stair geometry. Headroom must be at least 6 feet 8 inches. Landings are required at top, bottom, and at maximum intervals of 12 feet of vertical rise.
| Parameter | IRC | IBC |
|---|---|---|
| Maximum Riser Height | 7.75 in | 7 in |
| Minimum Tread Depth | 10 in | 11 in |
| Minimum Width | 36 in | 44 in |
| Handrail Height | 34-38 in | 34-38 in |
| Baluster Spacing | 4 in max | 4 in max |
Structural Design
Stairs must support minimum live loads of 40 psf residential and 100 psf commercial. For wood-framed stairs, 2×12 lumber is typically used for stringers with minimum throat depth of 3.5 inches after cutting. Wider stairs exceeding 36 inches require additional center stringers to prevent tread deflection.
Construction Methods
Total rise is divided by desired riser height to determine step count. Open-riser stairs must have treads overlapping stringers by at least 1 inch. Closed-riser stairs have riser boards closing the space between treads. Prefabricated components increasingly improve quality control and installation efficiency.
Railing Systems
Handrails must be continuous between landings and withstand 200 pounds applied in any direction. Handrail cross-section should be 1.25-2 inches in diameter with 1.5 inches clearance from walls. Balusters must prevent a 4-inch sphere from passing through. According to the National Safety Council, stairs are the second leading cause of home injuries, making slip-resistant treads critical.