Stair geometry
Stair geometry is the NCC residential dimensional set: riser 115-190 mm, going 240-355 mm, 2R+G 550-700 mm, max 5 mm variation, max 18 risers per flight.
Ask Chalkline about this →Stair geometry is the dimensional set governing residential stair construction: the riser height, going, slope relationship (2R + G), flight length, and uniformity tolerances that together make a stair compliant under ABCB Housing Provisions Part 11.2. The deeper detail lives in the NCC stair geometry regulation article.
The numbers in one place
| Dimension | Standard residential range |
|---|---|
| Riser (R) | 115 to 190 mm |
| Going (G) | 240 to 355 mm |
| 2R + G | 550 to 700 mm |
| Adjacent variation | ≤ 5 mm |
| Spread across a flight | ≤ 10 mm |
| Risers per flight | 2 to 18 |
(Verified 2026-05-28.)
Why the set matters as a group
The trap is treating each number on its own. A flight that hits the riser range, the going range, AND the 2R + G slope-relationship range will feel right and pass inspection. A flight that hits two of three falls foul of Part H5 on safe passage even if the individual numbers look fine on paper. The 2R + G band is the one builders most often miss.
Locking the geometry before structural framing
The cheap moment to fix stair geometry is before the floor framing goes in around the stair void. Set out the geometry, work back to a floor-to-floor height that divides cleanly by your chosen riser, and confirm the going fits the planned tread material. Rebuilding a stair after the upper floor is framed is the classic late-stage rework.
Category: Stairs / NCC Housing Provisions.
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See also
Last updated: 2026-05-28. Verified: 2026-05-28. Quarterly review for currency.