NZ stair calculator, built to D1/AS1
Enter the total rise and the tread depth and this returns the riser count, the rise per riser and the pitch, then checks all three against the D1/AS1 Table 6 limits for your stair class. There is no 2R+G rule in New Zealand and this does not apply one.
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. Applying an imported formula on top of that will reject stairs that are perfectly compliant and, worse, can pass ones that are not.
The four stair classes
D1/AS1 Table 6 works by stair class, and picking the wrong class is the other common error. The classes are Service and minor private, Secondary private, Common and main private, and Accessible. They get progressively more generous as more people use them and as the users become less familiar with the stair.
Note that main private and common are grouped together as one class. A stair is not put in a gentler class simply because it is the main one in a house.
Maximum rise between landings depends on the class
A private stair can climb further between landings than a common one. The calculator flags when the total rise exceeds the limit for the class you picked and tells you an intermediate landing is needed.
The distinction it draws attention to matters. The tighter figure applies to a common area, which means a stair shared between household units. A main stair inside a single household unit is a private stair and gets the more generous limit. Two physically identical stairs, different answer, decided by what the building is.
Headroom
Headroom on an access route is 2100mm, relaxed to 2000mm over the stairway itself. The relaxation is what makes a stair fit under an upper floor in a lot of houses, and it is the measurement most often missed when a stair is repositioned late in a design.
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
Built Simple runs scheduling, estimating and the crew from one app. Free to start.
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, and applying it in New Zealand will give you wrong answers in both directions.
What is the maximum stair pitch in New Zealand? It depends on the stair class. Service and minor private stairs are allowed the steepest pitch, accessible stairs the shallowest, with secondary private and common or main private in between. The calculator applies the D1/AS1 Table 6 figure for the class you select.
Tread or going, which is right in New Zealand? Tread. Going is the British and Australian term for the same measurement. New Zealand documents say tread, measured nosing to nosing.
How much rise is allowed between landings? It depends on the class. A private stair is allowed more than a common one. The calculator flags when you exceed the limit for the class you picked, and an intermediate landing of at least 900mm is the fix.
What headroom does a New Zealand stair need? 2100mm on an access route, relaxed to 2000mm over the stairway itself.
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. Free Acceptable Solution.
- F4/AS1 Safety from Falling, Ministry of Business, Innovation and Employment.
- building.govt.nz, for the current editions.
