NZ Stair & Barrier Rules: Riser, Tread, Handrails, Barriers

The requirement

For the main stair in a house, each riser can be no more than 190 mm tall. Each going must be at least 280 mm deep. Keep every riser in the flight the same height. Main private stairs also have a 37° maximum pitch in Table 6. The numbers come from D1/AS1, the deemed-to-comply Acceptable Solution under the NZ Building Code.

The riser is how tall each step is. D1/AS1 calls its 280 mm limit tread depth. Use its Figure 12 to measure that depth and any nosing. Do not confuse it with the timber board width. A stair has to be steep enough to fit the space. It also has to be shallow enough to climb safely. Secondary and service stairs are allowed to be a bit steeper. The table shows all three.

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 pitch line runs 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.

The gaps in a barrier matter too. A small child must not 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. You want an even, comfortable main stair.

1. 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 = 186.67 mm per riser (rounded for display). That is under the riser limit, but does not prove the whole stair complies.
2. 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.
3. Check the space before changing the count. At the same 280 mm going, 16 risers would need 15 goings and 4200 mm of run. Adding a riser lowers the rise but makes this straight flight longer. If 3920 mm does not fit, redesign the layout with the required landings and clearances. Keep every riser equal and recheck all applicable limits.

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). Official D1 PDF.
• 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 in the official F4 PDF.

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 propose 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.