Stair Geometry Code Check (IBC 1011 / IRC R311)
Whether a stair's riser, tread, and clear width meet the adopted code, the check every stair permit turns on: IBC (commercial) caps the riser at 7 in, floors the tread at 11 in, and needs 44 in of width; IRC (residential) allows a 7-3/4 in riser and a 10 in tread at 36 in. A 7-1/2 in riser is a legal residential stair and an illegal commercial one - the single most common tenant-improvement stair red-tag. Reports each dimension pass/fail against the selected code plus the 2R + T comfort read (24-25 in). Uniformity, nosing, landings, and winders are separate checks; the egress width from occupant load is the egress-capacity tile. A design aid, not a code-official determination; the AHJ governs.
Formula and source
IBC (commercial): riser 4-7 in, tread >= 11 in, width >= 44 in. IRC (residential): riser <= 7.75 in, tread >= 10 in, width >= 36 in. Each measured value is compared to its limit; 2R + T (comfort 24-25 in) is reported, not enforced.
IBC 2021 (International Building Code) §1011.5.2 (riser/tread) and §1011.2 (width), and IRC 2021 (International Residential Code) R311.7.5 (riser/tread) and R311.7.1 (width), by section; dimensional minimums only, not reproduced.
Audience
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Posture
Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.