What is the stair nosing requirement?
On stairs with solid risers, treads less than 11 inches deep must have a nosing that projects ¾ inch to 1¼ inches beyond the tread below (2018 IRC §R311.7.5.3). The nosing's leading edge may have a radius up to 9/16 inch or a bevel up to ½ inch, and the projection must be consistent within 3/8 inch across the flight.
Source: 2018 IRC §R311.7.5.3 · Verify against your AHJ and the adopted code edition.
The nosing is the lip of a tread that overhangs the riser below. It gives your foot a little extra landing depth without adding to the stair’s total run.
Under IRC §R311.7.5.3, on stairs with solid risers where the tread depth is less than 11 inches:
- The nosing must project ¾ inch to 1¼ inches past the face of the tread below.
- The projection must be uniform within 3/8 inch across the whole flight — the same tolerance that applies to riser and tread size.
- The leading edge can be rounded to a radius of 9/16 inch max, or beveled up to ½ inch.
If the treads are 11 inches or deeper, a nosing isn’t required (you already have the depth). Open-riser stairs have their own rules instead. Editions and local amendments vary — verify with your AHJ.
Work it out: the stair calculator sizes the riser and tread so you can see whether your run needs a nosing to hit the 10-inch minimum tread depth.
Sources
- ICC — International Codes (IRC) — 2018 IRC §R311.7.5.3