The requirement
A stair has to be steep enough to fit the space, but shallow enough to climb safely. The New Zealand Building Code sets this with two numbers you set out with a tape — the riser and the going — plus rules for headroom and the handrail. These come from the D1/AS1 Acceptable Solution, the deemed-to-comply path.
- Riser — how tall each step is.
- Going — how deep each step is, the flat part you stand on (some call it the tread).
For the main stair in a house, each riser can be no more than 190 mm and each going must be at least 280 mm deep. Keep every step the same height so the stair is safe to climb. Secondary and service stairs are allowed to be a bit steeper — see the table.
| Dimension | Main house stair | Secondary | Service / minor |
|---|---|---|---|
| Riser (max) | 190 mm | 200 mm | 220 mm |
| Going (min) | 280 mm | 250 mm | 220 mm |
Two more numbers finish the stair off:
- Headroom — at least 2100 mm clear above the stair. You can drop to 2000 mm over a short landing, or a stair or corridor under 2 m long.
- Handrail — set it 900–1000 mm above the pitch line (the line running up the front edges of the steps).
- Width — the Acceptable Solution does not fix a minimum width for a stair inside a house. Set it to suit the space. (The 900 mm figure is for common or accessible stairs, not a private home stair.)
Guards & barriers
A barrier stops people falling off an edge. Under F4/AS1 you need a barrier anywhere a person could fall 1 m or more. The height depends on where it is.
| Where | Barrier height |
|---|---|
| Stairs, ramps and their landings | 900 mm |
| Balconies, decks and internal floor edges | 1000 mm |
| Trigger — barrier required | wherever the fall is 1 m or more |
The gaps in a barrier matter too, so a small child can’t slip through:
- On a house barrier, a 100 mm sphere must not pass through any gap. (In housing the Code always treats the building as used by children under 6.)
- In the triangle formed by a stair’s riser, tread and rail, a 150 mm sphere must not pass.
Work it out on site
Say your floor-to-floor height is 2800 mm and you want an even, comfortable main stair.
- Pick how many risers. 2800 ÷ 190 (the tallest a riser can be) = 14.7. You can’t have part of a step, so round up to 15 risers. 2800 ÷ 15 = 187 mm per riser. That’s under the 190 limit — good.
- Set the going. Try 280 mm, the minimum for a main stair. Fifteen risers means 14 goings, so the stair runs 14 × 280 = 3920 mm along the floor. Check it fits the space you have.
- Even it up. If 15 risers don’t fit the run, try 16 (2800 ÷ 16 = 175 mm) and re-measure. Keep every riser the same height.
The calculator does this rounding for you and keeps the risers even.
Do it in 5 seconds
Related
- New Zealand Building Code hub — how the one national Code and its Acceptable Solutions work.
- NCC stair requirements (Australia) — the Australian numbers, for anyone comparing across the ditch.
Sources
- NZBC D1/AS1 — Access routes, Table 6 (riser and tread), clause 1.4 (headroom) and clause 6.0.6 (handrail height). The deemed-to-comply path for stairs.
- NZBC F4/AS1 — Safety from falling, Table 1 (barrier heights and the 1 m fall trigger) and clause 1.2.1 (barrier openings). Confirm each figure and the current amendment at building.govt.nz.
Read this first. New Zealand has one national Building Code, so these rules apply the same everywhere. But the numbers above are the Acceptable Solution (deemed-to-comply) path. A designer may instead use a Verification Method or an Alternative Solution, which can carry different numbers — so treat these as the standard path, not the only legal one. Always re-check the current amendment on building.govt.nz before you sign off.
Related building rules
More New Zealand rules