IRC stair code at a glance
These are the stair rules in the 2021 International Residential Code, section R311.7; the 2024 edition keeps the numbers and moves them to R318.7 (handrails to R320, guards to R321)[1][2].
| Rule | Requirement | Section |
|---|---|---|
| Stair width | at least 36 in clear above the handrail; 31-1/2 in at the rail with one handrail, 27 in with two | R311.7.1 / R318.7.1 |
| Headroom | at least 6 ft 8 in, measured plumb from the nosing line | R311.7.2 / R318.7.2 |
| Riser height | at most 7-3/4 in; no minimum | R311.7.5.1 / R318.7.5.1 |
| Tread depth | at least 10 in, nosing to nosing | R311.7.5.2 / R318.7.5.2 |
| Uniformity | largest riser or tread at most 3/8 in over the smallest in a flight | R311.7.5.1–.2 / R318.7.5.1–.2 |
| Nosing | 3/4 to 1-1/4 in; not required when treads are 11 in or deeper | R311.7.5.3 / R318.7.5.3 |
| Open risers | must stop a 4 in sphere where the stair is over 30 in above the floor | R311.7.5.1 / R318.7.5.1 |
| Flight rise | at most 151 in (12 ft 7 in) between floors or landings | R311.7.3 / R318.7.3 |
| Landings | as wide as the stair and at least 36 in deep | R311.7.6 / R318.7.6 |
| Walking surface | slope at most 1:48 | R311.7.7 / R318.7.7 |
| Handrail height | 34 to 38 in above the nosing line, flights of 4 or more risers | R311.7.8 / R318.7.8, R320.2 |
| Guards | 36 in (34 in on stairs) where the drop exceeds 30 in; 4 in sphere | R312.1 / R321.1 |
Before the 2018 edition the flight limit was 147 in[3]. Commercial buildings follow the IBC instead: risers 4–7 in and treads at least 11 in (IBC 1011.5.2)[4]; the 2027 IBC, now published, keeps those limits. The 2027 IRC is due in early 2027, and we will update this page when it is out.
Stair riser height and tread depth
Stair riser height is measured vertically between the leading edges of adjacent treads and may be at most 7-3/4 in under the IRC; tread depth is measured horizontally from nosing to nosing and must be at least 10 in[1]. Both are measured without carpet. The tallest riser in a flight may exceed the shortest by no more than 3/8 in, and the same goes for treads, so the first and last steps must match the rest. Where a tread is under 11 in deep, the nosing must project 3/4 to 1-1/4 in.
Stair width
A residential stair must be at least 36 in wide clear of obstructions above handrail height, and handrails may reduce that to 31-1/2 in (one side) or 27 in (both sides) at and below the rail[1]. Spiral stairs may be 26 in. Canada requires 860 mm for a dwelling stair[8]; England sets no minimum width for private stairs in dwellings, and Scotland asks for 900 mm[6][7]. For deck stairs, the AWC deck guide also uses 36 in[12].
Handrail code
A handrail is required on at least one side of every flight with four or more risers, 34 to 38 in above the nosings[1]. It must be graspable: a round rail is 1-1/4 to 2 in across, and a non-round rail has a 4 to 6-1/4 in perimeter. It runs the full flight, stands at least 1-1/2 in off the wall and returns to the wall or ends at a post.
- England: 900–1,000 mm above the pitch line; both sides on stairs 1 m wide or wider[6].
- Canada: 865–1,070 mm; not required on interior stairs of two risers or fewer[8].
- Australia: at least 865 mm, not required under 1 m of rise[10].
Guards on stairs and landings
Where an open side drops more than 30 in, the IRC requires a guard at least 36 in high on landings and floors and 34 in on the open side of a stair, with no opening that passes a 4 in sphere (4-3/8 in along a stair; 6 in at the triangle under the bottom rail)[1]. The baluster spacing calculator lays out the balusters.
Winders and spiral stairs
Winders need a 10 in tread at the walkline, 12 in in from the narrow side, and at least 6 in anywhere. Spiral stairs have their own limits: 26 in clear width, 6-3/4 in tread at the walkline, 9-1/2 in maximum riser and 6 ft 6 in headroom[1]. Try them in the spiral staircase calculator.
Stair codes outside the US
| Code | Riser | Going / run | Other |
|---|---|---|---|
| England[6] | 150–220 mm | 220–300 mm | 42° max pitch; 2R + G 550–700 mm; 2 m headroom |
| Scotland[7] | 100–220 mm | ≥ 225 mm | 42° max; 900 mm width; at most 16 rises per flight |
| Canada[8] | 125–200 mm | 255–355 mm | 860 mm width; 1,950 mm headroom; 3.7 m per flight |
| Australia[9][11] | 115–190 mm | 240–355 mm | 2R + G 550–700 mm; 2–18 risers; 2 m headroom |
Codes are adopted and amended locally: the IRC is used in 49 states but many cities change parts of it[5]. Run your numbers through the stair calculator with the code selector, or fit a stair to a space with the stair rise and run calculator.
Ask before you buildYour building department decides which edition applies and whether a permit is needed. Most stair work in a dwelling needs one.
Frequently asked questions
What is the minimum stair tread depth?
10 in under the IRC, measured nosing to nosing (11 in for commercial stairs under the IBC). England allows 220 mm, Canada 255 mm and Australia 240 mm for private stairs.
What is the code for stair risers and treads?
Under the IRC, risers at most 7-3/4 in and treads at least 10 in, all within 3/8 in of each other in a flight.
What is the maximum stair riser height?
7-3/4 in for US homes (IRC), 220 mm in England, 200 mm in Canada and 190 mm in Australia.
What is the minimum stair width?
36 in in US homes (IRC), 860 mm in Canadian dwellings and 900 mm in Scotland. England sets no minimum for private stairs.
When is a handrail required on stairs?
Under the IRC on every flight with four or more risers, 34 to 38 in above the nosings.
What is the headroom code for stairs?
6 ft 8 in in the US, 2.0 m in England and Australia, and 1,950 mm for a Canadian dwelling stair.
Sources
- 2021 International Residential Code, Chapter 3: Building Planning (R301.5, R311.7 stairways, R312 guards)
- 2024 International Residential Code, Chapter 3 (R318.7 stairways, R320 handrails, R321 guards)
- 2015 International Residential Code, Chapter 3 (147 in flight rise)
- 2021 International Building Code, Chapter 10: Means of Egress (1011.5.2, 1015.3)
- International Residential Code adoption map
- Approved Document K: Protection from falling, collision and impact (2013 edition, for use in England)
- Building Standards Technical Handbook 2022: Domestic, 4.3 Stairs and ramps
- National Building Code of Canada 2020, Division B, Part 9, Section 9.8 Stairs, ramps, handrails and guards
- ABCB Housing Provisions, Part 11.2 Stairway and ramp construction (NCC 2022)
- ABCB Housing Provisions, Part 11.3 Barriers and handrails (NCC 2022)
- ABCB Housing Provisions, Part 10.3 Room heights (stair headroom)
- DCA 6: Prescriptive Residential Wood Deck Construction Guide (2015 IRC basis)