Building Code Basics for Residential Stairs
The International Residential Code (IRC) sets minimum requirements: risers between 4” and 7¾”, treads at least 10” deep, and no more than 3/8” variation between the tallest and shortest riser in any staircase. Handrails are required when there are four or more risers, mounted 34–38 inches above the tread nosing.
The Comfort Rule: Rise + Run = 17–18 Inches
Builders use a simple rule of thumb: the sum of one riser height and one tread depth should fall between 17 and 18 inches. A 7” riser paired with a 10.5” tread (total 17.5”) is near ideal. Shallower stairs (lower risers, deeper treads) suit elderly users; steeper stairs save floor space in tight layouts.
How Total Rise Affects Riser Count
Divide your floor-to-floor height by your target riser height to get the number of risers. For a 108” rise at 7.25” per step: 108 ÷ 7.25 ≈ 14.9, so use 15 risers at exactly 7.2” each. The total run (horizontal footprint) equals (risers − 1) × tread depth, because the top landing replaces the last tread.
Frequently Asked Questions
How many stairs for a standard floor?
A standard 9-foot ceiling (108 inches total height with floor framing) needs about 14-15 risers at 7.25-7.5 inches each.
What stair angle is comfortable?
30-35° is ideal for residential stairs. Below 20° feels like a ramp; above 40° feels steep.