Stairs are among the most inspected parts of any job, and among the most dangerous when they're wrong. Small inconsistencies trip people, because we stop looking at our feet after the first step or two. These are the core rules for stairs in houses (Class 1 buildings) under the National Construction Code (NCC) Housing Provisions, Part 11.2 for stairs and Part 11.3 for barriers and handrails. Always confirm with your building surveyor or certifier, since states can add their own variations.
The key dimensions
| Item | Rule |
|---|---|
| Riser | 115–190 mm |
| Going | 240–355 mm |
| 2R + G | 550–700 mm |
| Risers per flight | 2 minimum, 18 maximum |
| Landings | At least 750 mm long |
| Headroom | 2.0 m minimum above the nosing line |
| Handrail | At least 865 mm above the nosings, where the stair rises more than 1 m |
| Balustrade | Where the drop is more than 1 m: at least 865 mm high on the stair, 1 m on landings and decks |
| Openings | 125 mm sphere must not pass (balustrades and open risers) |
Laying out a flight
- Measure the total rise from finished floor to finished floor. Allow for floor finishes at both ends: carpet, tile and screed all change it.
- Divide by the maximum riser and round up to get the number of risers.
- Divide the total rise by that number for the exact riser height.
- Treads = risers − 1. Total run = treads × tread depth.
- Check the total run fits the space, and check headroom along the whole flight against the floor or ceiling above.
- Work out the stringer length and the angle, then mark out a pattern stringer.
A comfortable house stair often lands around 175–185 mm rise and 250–280 mm going, giving a 2R + G of about 610–640 mm. The steeper the stair, the more it saves space but the harder it is to use, especially for children and older people.
Winders and landings
Winders (tapered treads that turn a corner) save space but need care. The NCC allows winders in place of a landing (no more than three in place of a quarter landing, and six in place of a half landing), with the going measured at the centre of the tread on stairs up to 1 m wide. Check the current NCC wording before building winders. Landings must be at least 750 mm long, with a gradient no steeper than 1:50. Where a door opens onto a stair that rises more than three risers (570 mm), a landing must run across the full width of the doorway.
Handrails and guards
A stair that rises more than 1 m needs a handrail on at least one side, at least 865 mm above the nosings. A balustrade is required where a stair, landing or deck is more than 1 m above the floor or ground below, with no opening a 125 mm sphere can pass. Where the drop is more than 4 m, rails or footholds between 150 and 760 mm above the floor that make the balustrade climbable aren't allowed. Guards must resist a set load, so fix posts and balusters properly, not just with nails into the trim.
Common failures
- The top or bottom riser is a different height because the floor finish wasn't allowed for.
- Headroom too low under a beam or at the edge of the stair opening.
- Balusters spaced just over the 125 mm limit.
- A missing handrail where one is required, or handrails that stop short of the last riser.
- Nosings missing or inconsistent, which changes the effective going.
- Gaps under open risers that a child could slip through.
External steps and decks
The same principles apply outside, and consistency matters even more on wet, uneven ground. Make every step the same, give treads a slight fall so water runs off, and add lighting for steps used after dark.
Pricing stairs
Stairs take far longer per material dollar than most carpentry. Allow time for setting out, cutting a pattern stringer, test fits, and the finish work on treads, nosings and handrails. A stair that's "nearly right" has to be rebuilt, so price enough time to get it right first.
The stair calculator runs these checks as you type, the spindle calculator spaces guards to the limit, and the ramp calculator covers access ramps.
A worked example
A floor-to-floor height of 2600 mm. 2600 ÷ 190 = 13.7, so 14 risers at 185.7 mm. That gives 13 treads; with a 250 mm going, the total run is 3.25 m. 2R + G = 621 mm and the angle is about 36.6°, comfortably within the rules. A 900 mm wide stair takes three stringers.
Common questions
Can I build a steeper stair to save space?
Only within the limits above. A riser of 190 mm and a going of 240 mm is as steep as a compliant house stair gets. Ladders and steep access stairs are a different matter, so ask your building surveyor or certifier before planning one.
Do deck and porch stairs follow the same rules?
Yes. Deck and verandah stairs follow the same riser, going and 2R + G rules, and need a handrail where they rise more than 1 m and a balustrade where the drop is more than 1 m. Use treated or durable timber and a slip-resistant tread or nosing.
Are open risers allowed?
Yes, but the gap between treads must not let a 125 mm sphere pass. A riser bar or a deeper tread closes the gap.
When is a handrail needed?
Where a stair rises more than 1 m, it needs a handrail on at least one side, at least 865 mm above the line of the nosings and running the full length of the flight. Many builders fit one to every stair anyway, because it costs little and people use it.
How many risers can one flight have?
Between 2 and 18. A longer stair needs a landing, at least 750 mm long, to break it into flights, and every riser and going within a flight must be the same.
Before you build
Mark out the stair at full size on the floor or a wall, including the floor finishes, to check headroom and landing space. Confirm the design with the inspector before cutting, especially for winders, open risers and attic conversions.
This guide is general information for estimating. It is not engineering, legal or tax advice. Check the NCC, Australian Standards and your building surveyor or certifier for your project.