Building materials · Reference
Under the US IRC, stairs need a maximum 7 3/4-inch (196 mm) riser, 10-inch (254 mm) tread, 36-inch (914 mm) width and 6-ft-8 (2032 mm) headroom. UK Part K caps private-stair rise at 220 mm, going 220 mm minimum, pitch 42°.
A stair step is specified by three dimensions: the rise (vertical step height), the going/run (horizontal tread depth) and the clear width of the flight.
| Dimension | US (IRC) | UK (Part K) |
|---|---|---|
| Maximum riser / riseIRC R311.7.5.1; Part K private-stair rise 150–220 mm | 7 3/4 in (196 mm) max | 220 mm (≈8 5/8 in) max — private stair |
| Minimum tread / goingIRC R311.7.5.2 (11 in / 279 mm if no nosing); Part K private stair | 10 in (254 mm) min | 220 mm min going, max 300 mm |
| Minimum stairway widthIRC R311.7.1; Part K para 1.15 | 36 in (914 mm) clear | Not set for private stairs; 1200 mm for non-dwellings |
| Minimum headroomIRC R311.7.2; Part K para 1.11 | 6 ft 8 in (2032 mm) | 2000 mm (≈6 ft 6 3/4 in) |
Source: ICC IRC Code & Commentary (R311.7) and UK Approved Document K, Table 1.1
| Rule | US (IRC) | UK (Part K) |
|---|---|---|
| Maximum pitch (angle) | Not directly limited (set by riser & tread) | 42° max (private stair) |
| 2R + G (rise/going) rule | Comfort rule of thumb, not codified | 2R + G = 550–700 mm (≈21.7–27.6 in) |
| Riser / tread uniformity | ≤ 3/8 in (9.5 mm) variation within a flight | One rise & going used throughout each flight |
Source: UK Approved Document K (2013, England) & ICC IRC R311.7.5
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Under the US IRC (R311.7.5.1) the maximum riser is 7 3/4 in (196 mm). UK Part K Table 1.1 caps a private-stair rise at 220 mm (≈8 5/8 in).
US IRC (R311.7.5.2) requires a minimum 10 in (254 mm) tread depth, or 11 in (279 mm) with no nosing. UK Part K requires a minimum going of 220 mm (≈8 5/8 in) for private stairs.
US IRC (R311.7.1) requires at least 36 in (914 mm) clear width. UK Part K sets no minimum width for private stairs, but requires 1200 mm (≈47 1/4 in) for stairs in buildings other than dwellings.
US IRC (R311.7.2) requires 6 ft 8 in (2032 mm). UK Part K (para 1.11) requires at least 2 m (2000 mm ≈ 6 ft 6 3/4 in).
UK Part K states that twice the rise plus the going (2R+G) should be between 550 mm and 700 mm (about 21.7–27.6 in) for comfortable, safe steps.
UK Part K limits a private stair to a 42° maximum pitch. The US IRC sets no explicit angle; the slope is instead governed by the 7 3/4 in (196 mm) max riser and 10 in (254 mm) min tread.
Every figure on this page is traced to a named source, linked under each table. Standard sizes come from published standards and established industry references; where a size is a typical range or varies by manufacturer, we say so. Sizes vary by region, model and revision — treat these as the standard reference, and confirm the exact spec of the item you are selling.
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