NCC stair geometry: riser, going and flight dimensions for Class 1 homes

TL;DR

For Class 1 residential stairs, NCC 2022 (via ABCB Housing Provisions Part 11.2) sets risers between 115 mm and 190 mm, goings between 240 mm and 355 mm, maximum 18 risers per flight. Adjacent risers and goings may vary by no more than 5 mm; total spread within a flight must not exceed 10 mm. Lock stair geometry before structural framing is complete: changing floor-to-floor height after the slab is poured forces a stair rebuild. For balustrade heights, barrier rules, and handrail requirements under the same Part H5, see NCC stairs, balustrades and handrails.

Scope

This article covers stair geometry only: dimensional limits for risers, goings, flights, landings, winders, and slip resistance for Class 1a, 1b, and Class 10a buildings. All dimensional values come from Part 11.2 of the ABCB Housing Provisions Standard 2022, which is the deemed-to-satisfy (DTS) path under NCC 2022 Volume Two Part H5.

For the full H5 picture including balustrade heights, the 125 mm sphere test, climbability restrictions, and handrail rules, see NCC stairs, balustrades and handrails.

Standard stair dimensions (habitable spaces)

The following limits apply to all stairs serving habitable rooms: bedrooms, living areas, kitchens, bathrooms, ensuite, laundry, and any stair a resident is expected to use regularly (Housing Provisions clause 11.2.2(1)).

Dimension	Minimum	Maximum
Riser height (R)	115 mm	190 mm
Going (tread depth, G)	240 mm	355 mm
Slope relationship (2R + G)	550 mm	700 mm

The slope relationship check (2R + G) is a comfort test. A riser of 180 mm with a going of 250 mm gives 2(180) + 250 = 610 mm, which falls within the 550 to 700 mm band and is compliant. A riser of 190 mm with a going of 240 mm gives 620 mm, also within band.

(Verified 2026-05-09 via ncc.abcb.gov.au/editions/ncc-2022/adopted/housing-provisions/11-safe-movement-and-access/part-112-stairway-and-ramp-construction.)

Non-habitable access stair dimensions

Stairs serving non-habitable spaces (storerooms, attics, ceiling access) carry less stringent geometry under clause 11.2.2(2).

Dimension	Minimum	Maximum
Riser height	130 mm	225 mm
Going	215 mm	355 mm

These stairs are typically used by the owner for occasional access, not as a primary circulation route. If any doubt exists about whether a space is habitable, use the habitable limits.

Spiral stairs

Spiral stairs have a separate geometry table because their tread shape means the going varies across the tread width. The limits below apply to the going measured at the walking line (clause 11.2.2(3)).

Dimension	Minimum	Maximum
Riser height	140 mm	220 mm
Going	210 mm	370 mm
Slope relationship (2R + G)	590 mm	680 mm

Uniformity within a flight

Riser and going uniformity is one of the most common stair defects at PCI because it is caused by cumulative small errors during framing and fit-out, not a single wrong measurement.

The rules under clause 11.2.2(1)(c):

Adjacent risers must not differ by more than 5 mm.
Adjacent goings must not differ by more than 5 mm.
The spread between the smallest and largest riser within a flight must not exceed 10 mm.
The same 10 mm spread rule applies across all goings within a flight.

Practical implication: if string lines, set-out, and stringer cutting are all square, the 5 mm and 10 mm tolerances are easy to meet. Problems arise when floor-to-floor height is measured at the wrong point (between finished floor levels, not subfloor to subfloor), or when timber treads are installed before acclimatisation and shrink unevenly after fixing.

Flight limits

Under clause 11.2.2(1)(a) and (1)(b):

Minimum 2 risers per flight.
Maximum 18 risers per flight.

A flight exceeding 18 risers requires a landing to break the run. The maximum 18-riser rule catches long straight stairs to upper floors: a floor-to-floor height of 3 m at 167 mm per riser equals 18 risers exactly. At a riser of 190 mm, 3 m gives only 15.8 risers, so 16 risers is the practical upper limit at that height.

Landings

A landing is required between flights when the total rise exceeds 3 risers or 570 mm (clause 11.2.5(1)).

Condition	Minimum landing length
Habitable stair landing	750 mm
Non-habitable stair landing	600 mm

Landing gradient must not exceed 1:50 (clause 11.2.5(3)). A door opening onto a stair run requires a landing where the level change applies: the door cannot swing directly onto the first stair nosing.

Winders

Winders are tapered treads used to turn a stair flight through a corner without a separate landing platform. They are permitted under clause 11.2.3 within the following limits:

Maximum 3 consecutive winders substituting for a quarter landing (90-degree turn).
Maximum 6 consecutive winders substituting for a half landing (180-degree turn).

Winder geometry follows the standard riser and going limits above, measured at the walking line (typically 225 mm from the narrow end of the tread). The narrow end of the winder must not be less than 50 mm wide (clause 11.2.3(1)(b)).

Winders are a chippy’s measurement challenge: each tread is a different shape, and the walking-line going must stay within the 240 to 355 mm band for habitable stairs.

Slip resistance

Slip ratings apply to all stair treads under Table 11.2.4 of the Housing Provisions. The required rating depends on the exposure condition of the tread.

Surface condition	Pendulum rating	Ramp rating
Internal dry treads	P3 or R10	P3 or R10
External or wet-exposed treads	P4 or R11	P4 or R11

External stairs, alfresco treads, stairs into a garage from a covered outdoor area, and any tread that can receive rain or splash fall into the wet/exposed category. Smooth hardwood, polished concrete, and glazed porcelain tile all require testing or product certification to confirm they meet P4/R11 in wet conditions.

Specifying the slip rating in the finishes schedule before procurement avoids a PCI hold when the tiler or flooring subbie supplies material that doesn’t meet the minimum.

(Verified 2026-05-09 via ncc.abcb.gov.au/editions/ncc-2022/adopted/housing-provisions/11-safe-movement-and-access/part-112-stairway-and-ramp-construction.)

What to lock before framing

Stair geometry is set by floor-to-floor height and horizontal run distance. Both are fixed by the structural framing. Changing either after the slab is poured or the frame is erected means rebuilding the stair.

Before framing is locked:

Measure floor-to-floor height as the finished floor level dimension, not the subfloor dimension. Tile, screed, and overlay thickness changes the riser count.
Confirm the stair type with the client and designer: standard, spiral, or winder. Each has different geometry rules and different stringer profiles.
Spec the tread finish and check the slip rating requirement. Changing tread material after the stringer is cut adds cost.
Confirm any door swing over the stair run. Doors require landings; a landing adds at least 750 mm to the horizontal run.

Common inspection failures at PCI

Defect	Root cause
Riser variation over 5 mm between adjacent treads	Floor-to-floor height measured on subfloor instead of finished floor; timber shrinkage after fixing
Going under 240 mm on standard stair	Horizontal run cut too short to fit the required riser count; builder reduced going to compensate
External treads rated P3 in wet area	Smooth hardwood or polished concrete specified without wet-area slip check
Landing depth under 750 mm	Stair designed to clear a lower ceiling or fit within a tight floor plan without checking landing rule
Winder narrow end under 50 mm	Winders set out from the corner post without applying the minimum narrow-end rule

Workmanship tolerances

Dimensional tolerances for riser variation, stringer squareness, and tread fixing are specified in the HIA Guide to Materials and Workmanship. HIA membership is currently deferred; verified workmanship tolerance values will be added when access is available. [HIA-071]

The NCC dimensional limits (riser 115 to 190 mm, going 240 to 355 mm, uniformity 5 mm adjacent / 10 mm spread) are the compliance floor. The HIA Guide documents the workmanship acceptance criteria inspectors apply at PCI.

What this article doesn’t cover

This article covers stair geometry only. The following are in NCC stairs, balustrades and handrails:

Barrier (balustrade) heights: when a barrier is required, minimum heights along stairways and on balconies/decks
Opening restrictions: the 125 mm sphere test and the 40 mm base gap limit
Climbability zone: horizontal element restrictions where falls exceed 4 m
Handrails: when required, height, graspability
Pool fencing (NCC Part H7, AS 1926.1)
Livable housing accessibility (NCC Part H8)

Source links

ABCB Housing Provisions Part 11.2 Stairway and ramp construction: https://ncc.abcb.gov.au/editions/ncc-2022/adopted/housing-provisions/11-safe-movement-and-access/part-112-stairway-and-ramp-construction
ABCB NCC 2022 Part H5 Safe movement and access: https://ncc.abcb.gov.au/editions/ncc-2022/adopted/volume-two/h-class-1-and-10-buildings/part-h5-safe-movement-and-access

References

Australian Building Codes Board, Part 11.2 Stairway and ramp construction, ABCB Housing Provisions Standard 2022. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/housing-provisions/11-safe-movement-and-access/part-112-stairway-and-ramp-construction (verified 2026-05-09).
Australian Building Codes Board, Part H5 Safe movement and access, NCC 2022 Volume Two. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/volume-two/h-class-1-and-10-buildings/part-h5-safe-movement-and-access (verified 2026-05-09).

NCC stairs, balustrades and handrails: the full Part H5 article including barrier heights, sphere test, handrail rules
ABCB Housing Provisions: where the DTS stair dimensions live
NCC 2022 Volume Two: full residential code overview
Chippy: the trade setting out and building the stair
Tolerance: what workmanship tolerance means on a building site
PCI: where stair defects are most commonly found and re-inspection fees are triggered
Deemed to satisfy: what DTS compliance means
Workmanship: general site workmanship standard