What are the D1/AS1 stair rules for a house in New Zealand?
Published · Updated · By Sai Nath
Acceptable Solution D1/AS1, Table 6, sets the house stair limits: a main private stairway has risers of 190 mm or less, goings of 280 mm or more and a pitch of 37° or less, and a secondary private stairway allows 200 mm, 250 mm and 41°. F4/AS1 puts the stair barrier 900 mm above the pitch line.
Which stair type is yours?
D1/AS1 Table 6 gives three limits for each type of stair: the tallest riser, the shortest tread depth (the going) and the steepest pitch. Pick the row by what the stair serves; the definitions are at the front of D1/AS1.
| Stairway | Riser, max | Going, min | Pitch, max | What it serves |
|---|---|---|---|---|
| Main private | 190 mm | 280 mm | 37° | Living areas, kitchens, garages and other frequently used spaces; every exterior private stair |
| Secondary private | 200 mm | 250 mm | 41° | A floor with only bedrooms, a bathroom or similar |
| Minor private, service | 220 mm | 220 mm | 47° | Minor: occasional access to one room that isn’t a living area or kitchen. Service: maintenance |
| Common | 190 mm | 280 mm | 37° | Stairs the public uses |
| Accessible | 180 mm | 310 mm | 32° | Stairs in buildings that must be accessible |
Outdoor steps catch people out: every exterior private stair is a main private stairway, so deck steps use 190 mm, 280 mm and 37° even if they only lead to the garden. Table 6 sets no minimum riser and no 2R + G range, unlike Australia’s NCC. A D1/AS1 comment adds that stairs flatter than 23° break a person’s stride.
How are the riser and going measured?
- Riser: from the top of one tread to the top of the next (Figure 12).
- Going: D1/AS1 calls it tread depth and measures it level from one nosing to the next, not across the board (Figure 12). A nosing may project up to 25 mm over a closed riser; with open risers the projection is 15 to 25 mm (4.1.6).
- Pitch: the angle of the pitch line, the line through the nosings, which is arctan(riser ÷ going).
- Uniformity: risers and tread depths in one flight within ± 5 mm, measured on the centreline of a straight flight (4.1.3).
That 5 mm goes quickly at the bottom step. Measure the total rise from finished floor to finished floor, so the tiles or carpet laid later don’t shorten the first riser.
Worked example: a 2.8 m floor-to-floor stair
A main private stair from the living floor to the floor above: 2800 mm finished floor to finished floor, under a 200 mm deep upper floor.
- Fewest risers: 2800 ÷ 190 = 14.7, rounded up to 15 risers of 2800 ÷ 15 = 186.7 mm. Under 190 mm.
- Treads: 15 − 1 = 14 treads at the 280 mm minimum, 14 × 280 = 3920 mm of going.
- Pitch: arctan(186.7 ÷ 280) = 33.7°. Under 37°.
- Headroom: 2000 mm, measured straight up from the pitch line (Table 1, Figure 3). The hole in the upper floor then has to run (200 + 2000) × 280 ÷ 186.7 = 3300 mm.
- Landings: one at the top and one at the bottom, each at least 900 mm long (4.3.1, 4.3.4). A private stair may rise 4.0 m between landings (Table 7), so 2800 mm needs no landing part way.
Two things follow, worked by hand from Table 6. With risers no taller than 190 mm and goings no shorter than 280 mm, the pitch can’t pass arctan(190 ÷ 280) = 34.2°, so the 37° never binds on a main private stair. And if the same stair served only bedrooms and a bathroom, the secondary row allows 2800 ÷ 200 = 14 risers of 200 mm and 13 treads of 250 mm: 3250 mm of going, 670 mm shorter, at arctan(200 ÷ 250) = 38.7°, under 41°. A stair set out with Australian numbers on a 240 mm going fails both rows; the NCC side is in stair requirements in Australia.
Doing it in MeisterCalc
Open Home ▸ Stairs, choose Rise Only and enter Total Rise 2800 mm and Going 280 mm. Under Advanced, keep Desired Riser Height at 190 mm, Floor / Joist Thickness at 200 mm and Headroom Height at 2000 mm, and tick Riser Limited. It shows Number of Risers 15, Actual Riser Height 186.7 mm, Number of Treads 14, Stairwell Opening 3300.0 mm and Incline Angle 33.69°. Its Total Run of 4200.0 mm is risers × going, one going more than the 3920 mm the treads cover. Stairs is free.
- Riser Limited rounds the riser count up, so no riser is taller than Desired Riser Height. Set that to the Table 6 maximum for your stair: 190 mm for main private, 200 mm for secondary private, 220 mm for minor private.
- Without Riser Limited, Rise Only takes the count from a 600 mm comfort rule, a target riser of (600 − 280) ÷ 2 = 160 mm: 18 risers of 155.6 mm and 17 treads, 4760 mm of going. That passes too, on a longer stair.
- In Rise Only the Incline Angle is the pitch of the nosing line. In Rise + Run it is total rise over total run, which comes out steeper, so check the 37° as arctan(riser ÷ going).
- The amber warnings use Australian figures (a riser over 190 mm or under 115 mm), not D1/AS1. A 200 mm riser on a secondary private stair is flagged although Table 6 allows it, and no warning is tied to the NZ 280 mm going.
Landings, handrails, headroom and winders
- Landings: at the top and bottom of every flight and where a door opens onto the stair, at least 900 mm long. A flight that rises 600 mm or less needs no landing at a door that slides or opens away from the steps (4.3.1, 4.3.4).
- Rise between landings: up to 4.0 m on a private stair (Table 7).
- Handrails: a stair up to 2.0 m wide with two or more risers needs one on at least one side, though a stair of two or three risers in or into a house can go without. The top of the rail sits 900 to 1000 mm above the pitch line, starts no higher than the second riser and runs the full flight (6.0.1, 6.0.4, 6.0.6).
- Headroom: 2000 mm above the pitch line (Table 1, Figure 3).
- Winders: allowed on private stairs when the risers match the straight flight, the tread depth on the pitch line is no less than on the straight flight, the taper is even and the winders turn through no more than 180° (4.5.1).
- Open risers: where children under 6 are likely, the gap between treads must not pass a 100 mm sphere (4.1.8).
- Width: D1/AS1 sets no minimum inside a household unit; its comment calls 850 mm a practical minimum for a private stair.
What barrier does a stair need?
Where people could fall 1 m or more, the Building Code asks for a barrier (clause F4.3.1). F4/AS1 Table 1 sets the minimum height:
| Building | Where | Barrier height |
|---|---|---|
| Detached house, or inside a household unit of a multi-unit dwelling | Stairs, ramps and their intermediate landings | 900 mm |
| Detached house, or inside a household unit of a multi-unit dwelling | Balconies, decks and the edges of internal floors or mezzanines | 1000 mm |
| Other buildings, and common areas of multi-unit dwellings | Stairs and ramps; most other places | 900 mm; 1100 mm |
On a stair the height is measured straight up from the pitch line or the nosings; on floors and landings, from the finished floor, ignoring carpet or vinyl (Table 1, Note 1). A handrail fixed on top of a stair barrier may rise to 1100 mm at an intermediate landing (Note 5), and F4/AS1 notes that a handrail can be part of the barrier, so one rail 900 to 1000 mm above the pitch line can serve as both.
The openings are the other half of the rule: in housing no gap may let a 100 mm sphere through, and the triangle under the bottom rail of a stair barrier must stop a 150 mm sphere (F4/AS1 1.2.1). The layout sums are in the maximum gap between balusters in New Zealand. In the app, set Baluster Spacing’s Max Spacing to 100; it starts at 125 mm.
Before you build
D1/AS1 (2nd edition, amendment 6) and F4/AS1 (3rd edition, amendment 2) have been in force since 1 January 2017 and were the current versions listed on building.govt.nz on 1 November 2026. They are one way to comply with clauses D1 and F4. Your consented plans and your building consent authority decide what your stair needs, so check with them before you cut a stringer.
Sources
Checked on 1 November 2026. These pages explain the rules; the code itself, your plans and your council, building consent authority, building control body or certifier decide what a job needs.
- MBIE, Acceptable Solution D1/AS1 Access routes, 2nd edition, amendment 6 (PDF): definitions of main, secondary and minor private stairways; Table 6; 4.1.3, 4.1.6, 4.1.8; Figures 3, 11 and 12; Table 1 height clearances; 4.3.1, 4.3.4 and Table 7 landings; 4.5.1 winders; 6.0.1, 6.0.4 and 6.0.6 handrails (checked 1 November 2026)
- MBIE, D1 Acceptable Solutions and Verification Methods: lists 2nd edition, amendment 6, effective 1 January 2017, as the current version (checked 1 November 2026)
- MBIE, Acceptable Solution F4/AS1 Safety from falling, 3rd edition, amendment 2 (PDF): Building Code clause F4.3.1; 1.1.1 and its comment; 1.2.1; Table 1 and its notes (checked 1 November 2026)
- MBIE, F4 Acceptable Solutions and Verification Methods: lists 3rd edition, amendment 2, effective 1 January 2017, as the current version (checked 1 November 2026)
Do the maths in MeisterCalc
MeisterCalc does the arithmetic behind these rules on an Android phone, with no signal needed: Stairs, Concrete and Check Square are free, and the other calculators come with Pro. It runs on Android 7.0 or later.