What is the minimum stair headroom?
Residential stairs need a minimum headroom of 6 feet 8 inches (80 inches), measured vertically from a line along the tread nosings to any ceiling or obstruction above (2018 IRC §R311.7.2). The clearance has to hold for the full width of the stairway and continue over the landings.
Source: 2018 IRC §R311.7.2 · Verify against your AHJ and the adopted code edition.
Headroom is the clear vertical space above the stairs. The IRC minimum is 6 feet 8 inches (80 inches), measured straight up from an imaginary line that runs along the tread nosings to the lowest thing overhead — a ceiling, a soffit, a duct, or the underside of the floor above.
Two things to watch:
- It applies over the whole width of the stair and continues over the landings, not just mid-flight.
- The tightest spot is usually at the top, where a bulkhead or the floor framing above closes in — check that point first when you lay out a stair under a sloped ceiling or in a basement.
The IBC sets the same 80-inch minimum for most stairs (§1011.3). Editions and local amendments vary — verify with your AHJ.
Work it out: the stair calculator gives the number of risers, the pitch, and the total run so you can check the diagonal headroom line against anything framed above the stairwell.
Sources
- ICC — International Codes (IRC) — 2018 IRC §R311.7.2