UK Stair Regulations Calculator (Part K)

In England and Wales, stairs are governed by Approved Document K of the Building Regulations (Scotland uses Section 4 of the Technical Handbooks with similar figures). Part K is structured differently from US codes: instead of one residential limit, it defines three stair categories, each with its own rise and going limits.

UK Approved Document K (Private) stair limits

Worked example — 9-foot floor-to-floor

For a 108-inch total rise under UK Approved Document K (Private): dividing by the 8.66-inch maximum riser gives a minimum of 13 risers. Spreading 108 inches evenly across 13 risers yields 8.31 inches per riser — within the limit and uniform, as the code requires.

Run your stair against UK Approved Document K (Private)

The three Part K stair categories

Part K sets dimensional limits by stair type rather than a single residential figure. Getting the category right is the most common compliance question on UK projects:

• Private (one dwelling): max rise 220 mm, min going 220 mm, max pitch 42°.
• Utility (escape, access for maintenance): max rise 190 mm, min going 250 mm.
• General access (public / common stairs in flats and non-dwellings): max rise 170 mm, min going 250 mm.

A stair serving more than one dwelling is a common stair and must meet the general-access limits (170 mm rise, 250 mm going) — not the more generous private limits. Using a 220 mm rise on a shared stair is among the most frequent failures on HMO and flat-conversion projects.

Other Part K rules to know

Part K also applies the "2R + G" comfort rule, expecting twice the rise plus the going to fall between 550 and 700 mm. Open risers must not allow a 100 mm sphere to pass, with treads overlapping at least 16 mm. A private flight is generally limited to 16 risers before a landing is required, and minimum headroom is 2.0 m (relaxed to 1.8 m at the centre for constrained loft conversions).

Other codes

Compare with IRC 2018, IRC 2021, IRC 2024, IBC, Australia NCC / BCA, Eurocode / EN.