We get asked this question a lot, so we’ve put together a dedicated page with the basic compliance information for residential spiral and curved stairs.

Our goal is to summarise the key points, so you don’t have to dig through hundreds of pages in the NCC to figure it out yourself. All you need to do is follow this process below:

1. Identify what type of staircase you have – spiral or tapered treads.
2. Determine the width of the unobstructed path.
3. Understand where the going(s) are measured from and how to calculate them.
4. Measure the rise height.
5. Calculate the slope relationship.

The first thing to do is clarify which type of curved stair you’re dealing with, from a compliance point of view. You’ve probably heard terms like spiral, helical, and elliptical — and might be wondering what the actual difference is?

There are two main types we’ll cover:

– Spiral Staircases
– Tapered Tread Staircases (which includes helical stairs)

Even if your stair looks “spiral” in shape, it doesn’t necessarily mean it’s technically classified as a spiral stair under the NCC. Here’s a couple important definitions explaining the types of stairs we are covering today.

NCC Definition of a Spiral Staircase:
“Spiral stairway: A stairway with a circular plan, winding around a central post with steps that radiate from a common centre or several radii.” (See Figures 11.2.2d and 11.2.2e in the ABCB Housing Provisions)

So — if your stair has a centre supporting post or column, it’s a spiral staircase.
NCC Definition of a Tapered Tread Staircase:
“Tapered tread: A stair tread with a walking area that grows smaller towards one end.”
If your staircase is curved without a centre post, such as a helical stair, it is classified as having tapered treads, not a spiral.

Theres another important dimension we will need for this exercise and that’s called the Unobstructed Path.

Definition from the NCC:
“Unobstructed path (or unobstructed width): The continuous, clear space along the stair flight that allows safe and unimpeded movement by users. This includes the full width free from any physical obstructions like handrails, posts, doors, protrusions, or overhead hazards.”

In most cases, this will be the clear walking width between the inner wall of the balustrade and the handrail. Be careful not to confuse this with tread width.
This table below gives you a good example.

Theres another important dimension we will need for this exercise and that’s called the Unobstructed Path.

Definition from the NCC:
“Unobstructed path (or unobstructed width): The continuous, clear space along the stair flight that allows safe and unimpeded movement by users. This includes the full width free from any physical obstructions like handrails, posts, doors, protrusions, or overhead hazards.”

In most cases, this will be the clear walking width between the inner wall of the balustrade and the handrail. Be careful not to confuse this with tread width.
This table below gives you a good example.

Once you’ve identified whether your stair is a spiral or has tapered treads and you have worked out what your unobstructed path is, you’ll need to calculate the goings. Each type has different methods and requirements for measuring goings, rises, and slope relationships.

Let’s start with Spiral Stairs (remember, spiral stairs must have a centre column or pole in the middle):
Spiral stairs have a single going per tread, and that going is measured at 7/10ths of the width of the unobstructed path.

Tapered Tread Stairs (e.g., Helical, Elliptical):
– If the unobstructed path is less than 1 metre: measure one going per step at the midpoint of the unobstructed path.

A riser is the vertical height between one tread and the next. It determines how high a person must lift their foot from step to step. The NCC specifies limits and consistency requirements for riser heights.

Now that you have the rise and going measurements, you can calculate the slope relationship — this tells you how steep or shallow your stairs are.

Simple Formula:
(Rise × 2) + Going = Slope Relationship

Example:
If the rise is 188 mm and the going is 250 mm:
(188 × 2) + 250 = 626

Your rises, goings and slope relationship must fall within the NCC-specified range for the type of stair you are building. Here’s a snippet of the table below.

This page only covers the basics of stair compliance. For anything more advanced, it’s always best to work with professionals who understand the NCC and deal with stair design every day — like us.

We’ve had countless clients come to us after getting burned by unqualified or overseas suppliers selling non-compliant staircases.

One client had to throw a $50,000 staircase in the bin that didn’t meet compliance so we could install a new one. The cost of rectification is enormous.

– All goings and risers must be consistent, but the NCC allows up to 5 mm variation between steps, so don’t let your certifier push you around on this one.
– Handrail height must be between 865 mm and 1000 mm — we recommend aiming for 900 mm.
– No gaps in the stair (like open risers) should allow a 125 mm sphere to pass through — use features like drop-down nosings to help with this.

– You must have a handrail to at least one side of the staircase, obviously curved stairs, the larger side of the staircase is the best place to have this.

– Does your stair have more than 18 rises or something else non-compliant? There’s times when you can get an access consultant to write a performance solution which will allow the certifier to sign it off. So for a few extra dollars, you may be able to bend the rules a bit.