NZ stair rules: the D1/AS1 limits
In New Zealand the stair class sets the limits, and the class follows what the stair serves. A stair up to a floor with only bedrooms and bathrooms is secondary private, and D1/AS1 Table 6 allows it a riser of up to 200mm, a tread of at least 250mm and a pitch of no more than 41°. A stair to living areas, a kitchen or a garage, and every outside private stair, is main private: 190mm, 280mm and 37°. A service or minor private stair can go to 220mm, 220mm and 47°. There is no 2R+G rule in New Zealand. Enter the total rise and the tread depth below and the calculator returns the riser count, the rise per riser and the pitch, and checks them for your stair class.
Last updated 26 October 2026. Limits from D1/AS1 Tables 6 and 7, Access Routes second edition amendment 6, in effect since 1 January 2017.
New Zealand has no 2R+G rule
This is the correction worth making loudly, because half the stair advice aimed at New Zealand builders is imported from British or Australian sources that do have one.
The United Kingdom uses twice the rise plus the going, and requires it to land between 550mm and 700mm. Australia has its own relationship. D1/AS1 does not. It sets maximum pitch, maximum riser and minimum tread independently, and a stair satisfies the Acceptable Solution when all three are met. Running an imported formula as an extra check only adds rejections: a 190mm riser with a 400mm tread gives 2R+G of 780mm, outside the British band, and it is a compliant main private stair. Using the formula instead of Table 6 is worse, because it passes stairs that fail: a 210mm riser with a 250mm tread gives 670mm, inside the band, and that riser is over the 200mm secondary private limit.
The stair class follows what the stair serves
D1/AS1 Table 6 has four rows, and which one a stair falls in is set by what it serves, not by whether it is the main stair in the house. Picking the wrong class is the other common error. A private stair is one used by the occupants of a single household unit, and the definitions at the front of D1/AS1 split it three ways.
- Main private serves frequently used spaces such as living areas, kitchens and garages. Every outside private stair is main private too, so deck and entry stairs take these limits.
- Secondary private serves another floor containing only bedrooms, bathrooms or similar. That is the usual stair in a two storey house with the living areas downstairs, and it stays secondary even when it is the only stair in the house.
- Minor private is off the main thoroughfare and gives infrequent access to a single room that is not a living area or kitchen. It shares a row with service stairs, used infrequently by service personnel for maintenance and moving goods.
- Common is any stair used by the public, whether as of right or not, that is not private, service or accessible. A stair shared between household units is common, and so is a stair in a shop or an office.
| Stair class | Maximum riser | Minimum tread | Maximum pitch | Rise between landings |
|---|---|---|---|---|
| Service, minor private | 220mm | 220mm | 47° | 4.0m |
| Secondary private | 200mm | 250mm | 41° | 4.0m |
| Main private | 190mm | 280mm | 37° | 4.0m |
| Common | 190mm | 280mm | 37° | 2.5m |
| Accessible | 180mm | 310mm | 32° | 2.5m |
Riser, tread and pitch from D1/AS1 Table 6, where common and main private share a row. Rise between landings from Table 7, which groups them differently: private and service stairs 4.0m, common and accessible 2.5m.
Maximum rise between landings depends on the class
D1/AS1 Table 7 caps the rise between landings at 4.0m for a private or service stair and 2.5m for a common or accessible one. A stair inside a house is private, so it can climb a full storey in one flight. A stair shared between household units is common, so the same flight in a block of units needs an intermediate landing once it rises more than 2.5m. Two physically identical stairs, different answer, decided by who uses them. The calculator flags when the total rise passes the limit for the class you picked.
Landings
Paragraph 4.3.1 asks for a landing at the top and bottom of every flight, and where a door opens into the stairway. The one exception: no landing is needed between a flight and a door where the flight rises no more than 600mm and the door slides or opens away from the steps. A landing is at least 900mm long (4.3.4) and no narrower than the access route it serves (4.3.3). Where landings are more than 8.0m apart vertically, the line of sight between them has to be broken by offsetting the flights, turning one by at least 30°, or a landing at least 1800mm long (4.3.6), which mostly matters on a stair running through several storeys.
Headroom
D1/AS1 Table 1 sets 2100mm of height clearance on a pedestrian access route of unlimited length, and 2000mm for "landings, stairways and corridors (less than 2 m in length)". Read that qualifier before relying on the lower figure. The text does not make clear whether it reaches a stair, and a flight up a full storey is well over 2m long, so 2100mm is the safe design figure. Headroom is the dimension most often lost when a stair is moved late in a design.
Width and handrails
D1/AS1 sets no minimum width for a stair inside a household unit. Paragraph 4.2.1 requires at least 900mm between handrails on an accessible stair, and between handrail and wall on a common stair. Its comment notes that C/AS2 requires 850mm for stairs in multi unit dwellings and calls that a practical minimum for any private stair.
Any stair up to 2.0m wide with two or more risers needs a handrail on at least one side, but one of two or three risers within, or giving access to, a household unit can go without (6.0.1). Over 2.0m wide it needs handrails on both sides and, past 4.0m, another down the centre, unless it is essentially an outdoor architectural feature, such as wide steps up to a deck, and not required to be accessible, in which case one is enough (6.0.2). Accessible stairs have them on both sides. The rail follows the pitch line, starts no further than the second riser from the bottom and runs the full length of the flight (6.0.4), and its top sits 900mm to 1m above the pitch line (6.0.6).
Tolerance, nosings and open risers
Every riser and every tread in one flight must match within 5mm either way, measured at the centreline of a straight flight (4.1.3). On a stair with closed risers the nosing can project up to 25mm, and with open risers the projection is 15mm to 25mm (4.1.6). A service stair with treads under 250mm must have open risers (4.1.5). In areas frequented by children under six, the gap between treads must not let a 100mm sphere through (4.1.8), so an open riser stair in a home with young children needs the gaps closed down.
Shallow is not automatically safer. A comment to 4.1.1 warns that a pitch line under 23° does not let a person use the stair with an acceptable gait, and that dangerous falls happen where the rhythm of movement is broken. The calculator flags a pitch under 23°.
Barriers are F4, not D1
Stair geometry is D1 Access Routes. The barrier alongside it is F4 Safety from Falling, a different clause with a different Acceptable Solution. If you are checking a stair, check both.
One warning about barriers specifically. New Zealand does not set a numeric non climbable zone the way Australia does. If you have seen a 150mm to 760mm rule, that is Australian and it does not transfer. F4/AS1 addresses climbability differently, so read it rather than importing a number.
The stair is one line on the programme
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Start free with Built SimpleFrequently Asked Questions
Is there a 2R+G rule in New Zealand? No. D1/AS1 sets maximum pitch, maximum riser and minimum tread independently. The 2R+G formula is British. Used as an extra check it rejects compliant New Zealand stairs, and used in place of Table 6 it passes stairs that fail.
What is the maximum stair pitch in New Zealand? It depends on the stair class: 47 degrees for a service or minor private stair, 41 for secondary private, 37 for main private and common, and 32 for accessible (D1/AS1 Table 6). D1/AS1 also warns against going under 23 degrees, which breaks the rhythm of walking.
Tread or going, which is right in New Zealand? Tread. D1/AS1 talks about tread depth and never uses going, the British and Australian term. Its Figure 12 shows how rise and tread depth are measured, so work from that drawing rather than an overseas method.
How much rise is allowed between landings? 4.0m for a private or service stair and 2.5m for a common or accessible one (D1/AS1 Table 7). Past that the stair needs an intermediate landing at least 900mm long and no narrower than the access route it serves.
What headroom does a New Zealand stair need? 2100mm on a pedestrian access route. D1/AS1 Table 1 allows 2000mm for landings, stairways and corridors less than 2m in length, so design a full flight to 2100mm.
Does a house stair need a handrail? Yes, on at least one side once it has two or more risers, with its top 900mm to 1m above the pitch line (D1/AS1 6.0.1 and 6.0.6). A stair of two or three risers within, or giving access to, a household unit can go without one.
What is the minimum stair width in a New Zealand house? D1/AS1 sets none inside a household unit. It requires 900mm on common and accessible stairs, and its commentary calls 850mm a practical minimum for any private stair.
Where are the barrier requirements? In F4 Safety from Falling, not D1. They are separate clauses. New Zealand has no numeric non climbable zone, so do not apply the Australian 150mm to 760mm rule.
Related calculators and guides
Sources
- D1/AS1 Access Routes, second edition amendment 6, Ministry of Business, Innovation and Employment, in effect since 1 January 2017: Definitions, Table 1 (height clearances), 4.1 and Table 6 (pitch, risers and treads), 4.2.1 (width), 4.3 and Table 7 (landings), 6.0 (handrails). Free Acceptable Solution.
- F4/AS1 Safety from Falling, Ministry of Business, Innovation and Employment.
- building.govt.nz, for the current editions.
