NCC Balustrade Requirements: Heights, Gaps, Climbability, Glass and Wire Barriers (2025 Guide)
Every NCC balustrade figure in one place: the 1 m fall trigger, 1 m and 865 mm heights, the 125 mm sphere and 40 mm face gap, the 150 to 760 mm climbability zone above 4 m, wire barrier tables, AS 1288 glass rules and the 2 m and 4 m openable window limits.
NCC balustrade requirements come down to a handful of numbers: a barrier where the fall is 1 m or more, a height of 1 m on a balcony or deck (865 mm on a stair), no opening that lets a 125 mm sphere through, and nothing to climb on between 150 mm and 760 mm where the drop is more than 4 m. Openable windows have their own set: protection where a bedroom floor is 2 m or more above the ground, 4 m for other rooms. This guide walks through each figure in the ABCB Housing Provisions and NCC Volume One, what AS 1288 asks of a glass balustrade, how the wire barrier tables work, and what has changed between NCC 2022 and NCC 2025. Stair flights and stair handrails are in the stairs guide.
The short answer
For a house or its garage (Class 1 and 10), Part 11.3 of the ABCB Housing Provisions applies. A continuous barrier is required along the side of any balcony, deck, verandah, mezzanine, landing or roof top space where it is possible to fall 1 m or more (11.3.3). It must be at least 1 m high above the floor of those places, or 865 mm above the nosings on a stair flight (11.3.4(2)); its openings must not let a 125 mm sphere through (11.3.4(4)); and where the fall is more than 4 m it must have no horizontal element between 150 mm and 760 mm above the floor that facilitates climbing (11.3.4(8)). A glass barrier must also comply with H1D8, which calls up AS 1288 for glazing used in balustrades (11.3.4(10)), and every barrier except a window serving as a barrier is designed for the loads in AS/NZS 1170.1 (11.3.4(11)).
For every Class 2 to 9 building, NCC Volume One D3D17 to D3D21 carry the same figures and D3D29 covers openable windows. The numbers are identical in NCC 2022 and NCC 2025, so the edition in force in your state changes the clause numbers you cite, not the dimensions you build to.
1. When a barrier is required: the 1 m rule
Housing Provisions 11.3.3(1) requires a continuous barrier along the side of a trafficable surface where it is possible to fall 1 m or more, measured from the level of the trafficable surface to the surface beneath. The clause lists a stairway or ramp; a floor, corridor, hallway, balcony, deck, verandah, mezzanine or access bridge; a roof top space to which general access is provided; and any delineated path of access to a building. Volume One D3D17(1) uses the same list and the same trigger.
Three exemptions appear in 11.3.3(2): a retaining wall, unless it forms part of a delineated path of access to the building from the road or between buildings; a barrier to an openable window, which 11.3.7 and 11.3.8 deal with; and a barrier complying with AS 1657 serving a fixed platform, walkway, stairway or ladder under 11.2.7(a). D3D17(2) adds the perimeter of a stage, rigging loft or loading dock, and the plant rooms and rarely used non-habitable rooms covered by D3D23.
2. Barrier height: 1 m on the balcony, 865 mm on the stair
Housing Provisions 11.3.4(2) sets two heights. The barrier must be not less than 1 m above the floor of any landing, corridor, hallway, balcony, deck, verandah, access path, mezzanine, access bridge or roof top space to which general access is provided. On a stair flight or ramp it must be not less than 865 mm above the nosings of the treads or the floor of the ramp. A landing barrier may also drop to 865 mm where it runs along the inside edge of the landing and does not exceed 500 mm in length, and a transition zone may be used where the height steps from 865 mm on the flight to 1 m at the landing (11.3.4(3)).
Volume One D3D18(1) gives the same figures: 865 mm for stairways or ramps with a gradient of 1:20 or steeper, 865 mm for the short inside-edge landing barrier, and 1 m for all other locations. Heights are measured vertically from the surface beneath, except on stairs, where they are measured above the nosing line (D3D18(2)).
One state variation applies. NSW D3D18(1) rewrites the auditorium case and, for a Class 9b entertainment venue, requires 1 m for stairways, ramps and access paths inside the building and 1200 mm where they are external. Nothing else in the barrier provisions is varied by any state in NCC 2025, and Part 11.3 of the Housing Provisions is national text.
3. Openings: the 125 mm sphere and the 40 mm face gap
Housing Provisions 11.3.4(4) is the gap rule most people are searching for: openings in barriers, including decorative balustrades, must not permit a 125 mm sphere to pass through. The sphere is the test, and it applies between balusters, below the bottom rail, between panels and at posts. On a stair the opening is measured above the nosing line (11.3.4(4); D3D19(1) and (5)).
A second dimension catches face-fixed barriers. Where a required barrier is fixed to the vertical face forming the edge of a landing, balcony, deck or stairway, the opening between the barrier and that face must not exceed 40 mm, measured horizontally from the edge of the trafficable surface to the nearest internal face of the barrier (11.3.4(5) and (6); D3D19(6) and (7)).
4. Climbability: the 150 mm to 760 mm zone above a 4 m fall
Where it is possible to fall more than 4 m, any horizontal element within the barrier between 150 mm and 760 mm above the floor must not facilitate climbing (11.3.4(8)). The 4 m is measured from the floor of the trafficable surface to the surface beneath. Volume One D3D20 applies the same zone to a barrier on a floor more than 4 m above the surface beneath, exempting internal emergency areas and Class 7 non-carpark and Class 8 buildings.
In practice this rules out horizontal rails, horizontal wires and any ledge wide enough to stand on in that band on a second-storey balcony and above. Vertical balusters, glass panels and vertical wires pass; a mid-rail at 600 mm does not. The explanatory note under 11.3.4 adds that where a window forms part of a barrier, a sill, transom or rail between 150 mm and 760 mm is deemed to facilitate climbing.
5. Wire barriers: the tension and deflection tables
A wire barrier is deemed to meet the 125 mm sphere rule if it is built to Housing Provisions 11.3.6 (11.3.4(9)); Volume One D3D21 does the same job for Class 2 to 9 buildings.
Horizontal wires (11.3.6(2)). Either the tension measured with a strain indicator meets Table 11.3.6a, or the deflection under a 2 kg mass hung at mid-span does not exceed Table 11.3.6b. Table 11.3.6a is indexed by wire diameter (2.5, 3.0 or 4.0 mm), lay (7x7, 1x19 or 7x19), wire spacing (60, 80 or 100 mm) and clear distance between posts (600 mm to 2500 mm). The numbers climb quickly: 2.5 mm 7x7 wire at 80 mm spacing needs 382 N with posts at 600 mm, 730 N at 900 mm and 1,288 N at 1,500 mm; from 1,800 mm the cell reads "x", meaning the combination is not permitted.
Continuous vertical wires (11.3.6(4)). Wires of not more than 2.5 mm diameter with a 7x7 or 7x19 lay, changes of direction around a pulley block, supporting rails not more than 900 mm apart, and tension in the span furthest from the tensioner to Table 11.3.6c, from 130 N (7x7 at 80 mm spacing) to 610 N (7x19 at 110 mm).
6. Glass balustrades: what AS 1288 adds
Housing Provisions 11.3.4(10) requires a glass barrier, or a window serving as a barrier, to comply with H1D8 as well as the height, opening and climbability rules. H1D8(2)(b) lists glazing used in balustrades among the assemblies that must be designed and constructed to AS 1288, and Section 7 of AS 1288:2021, "Barriers or balustrades", is the part that applies.
Clause 7.1 classifies glass panels as structural or infill; an infill panel is not required to resist line loads along its top edge because the handrail does that. Clause 7.2 classifies handrails as load supporting (fixed to the structure, normally used with infill), non-load supporting (fixed to the glass and relying on it), or interlinking, which must resist the design loads in the event that any one glass panel, including an end panel, has been broken. Clause 7.4 then sets the glass:
Grade A safety glass in all barriers, and no monolithic toughened glass in a barrier protecting a fall of 5 m or more (7.4.1).
A structural barrier protecting a difference in level of 1 000 mm or more with an interlinking handrail: monolithic toughened, laminated heat-strengthened or laminated toughened safety glass at a minimum 10 mm, with the handrail connected to the structure at either end or to three or more adjacent panels each at least 1 000 mm wide (7.4.5).
A structural barrier at 1 000 mm or more with no handrail or a non-load supporting one: laminated glass only, designed to 3.3.2 or tested to Appendix H, and limiting outward deflection after failure of all layers to 250 mm under a 200 N serviceability load (7.4.6). Note 4 says there is no deemed-to-satisfy solution for this configuration.
The loads come from AS/NZS 1170.0, 1170.1 and 1170.2 (7.3.1), applied at 1 000 mm or at the barrier height if lower.
7. Openable windows: the 2 m and 4 m rules
In a house, 11.3.7 covers bedrooms and 11.3.8 every other room; in a Class 2 or 3 building or Class 4 part, D3D29 covers both and also brings in Class 9b early childhood centres.
Bedrooms (11.3.7; D3D29(1)). Protection is required where the floor below the window is 2 m or more above the surface beneath. If the lowest level of the opening is less than 1.7 m above the floor, the openable portion must be protected by a device that restricts the opening or a screen with secure fittings. That device or screen must not permit a 125 mm sphere to pass, must resist an outward horizontal action of 250 N, and must have a child-resistant release mechanism if it can be removed, unlocked or overridden (11.3.7(2)). Where it can be released, a barrier not less than 865 mm above the floor is also required, and that barrier must stop a 125 mm sphere and have no climbable element between 150 mm and 760 mm (11.3.7(3) and (4)). If the openable part is at least 1.7 m above the floor, no further protection is required.
Other rooms (11.3.8; D3D29(3)(b)). The trigger is 4 m or more. Protection is a barrier not less than 865 mm above the floor that stops a 125 mm sphere and has no climbable element between 150 mm and 760 mm.
The explanatory notes settle the site questions. A wall or fixed glazing whose transom is at least 865 mm above the floor can be the barrier. A screen pop-riveted to the frame so it cannot be removed without a drill is a fixture, not a release mechanism, so the 865 mm barrier is not needed. D3D29(5) lets a window barrier in a fire-isolated stair or a Class 7 non-carpark or Class 8 building stop a 300 mm sphere instead.
8. Loads: AS/NZS 1170.1, and the window exception
A barrier, except a window serving as a barrier, must be designed to take loading forces in accordance with AS/NZS 1170.1 (11.3.4(11)). The note to 11.3.1 explains the exception: a window forming part of a barrier is designed under the glazing provisions of Section 8, which consider wind loading and human impact, and Section 8 exempts it from AS/NZS 1170.1.
9. NCC 2022 versus NCC 2025, and which one applies to you
Every figure in this guide is unchanged between NCC 2022 and NCC 2025. The 2022 text of Housing Provisions 11.3.3, 11.3.4, 11.3.7 and 11.3.8, and of Volume One D3D17 to D3D20 and D3D29, carries the same 1 m, 865 mm, 125 mm, 40 mm, 150 mm to 760 mm, 4 m, 2 m, 1.7 m and 250 N values under the same clause numbers, and the wire barrier rules in 11.3.6(4) are word for word the same.
So the edition question affects your citations, not the barrier. Victoria, Tasmania, Western Australia and the ACT apply NCC 2025 from 1 May 2026; New South Wales, Queensland and South Australia stay on NCC 2022 until 1 May 2027; the Northern Territory remains on NCC 2022. The state-by-state adoption guide tracks the transition rules.
Checklist
Fall height measured from the finished trafficable surface to the finished surface beneath; barrier required at 1 m or more (11.3.3 / D3D17).
Height 1 m above the balcony, deck, landing or mezzanine floor; 865 mm above nosings on the flight; transition zone drawn (11.3.4(2) and (3) / D3D18).
No opening passes a 125 mm sphere; face-fixed barriers within 40 mm of the floor edge (11.3.4(4) to (6) / D3D19).
Where the fall exceeds 4 m, no horizontal element between 150 mm and 760 mm, including window sills and transoms (11.3.4(8) / D3D20).
Wire: tension to Table 11.3.6a or 11.3.6c, or deflection to Table 11.3.6b; no combination marked "x" (11.3.6 / D3D21).
Glass: Grade A safety glass, structural or infill classification, handrail type, minimum 10 mm structural panels at 1 m or more, laminated only where there is no load-supporting or interlinking handrail (AS 1288:2021 Section 7).
Bedroom windows 2 m or more above ground: sill at 1.7 m, or restrictor or screen to 125 mm and 250 N with child-resistant release plus an 865 mm barrier; other rooms at 4 m or more: 865 mm barrier (11.3.7, 11.3.8 / D3D29).
Check it against the source
AEC Assistant searches the full text of NCC 2025 and NCC 2022 and Australia-wide planning information, resolves the edition in force for the state you are working in, and returns the clause that applies to your project with the source alongside it. Paid plans add deeper knowledge of the standards the code references. Try it free. No credit card.
Sources: ABCB Housing Provisions 2025 clauses 11.3.1, 11.3.3, 11.3.4, 11.3.6, 11.3.7 and 11.3.8 and Tables 11.3.6a, 11.3.6b and 11.3.6c, with their explanatory notes; NCC 2025 Volume One D3D17, D3D18 (including NSW D3D18), D3D19, D3D20, D3D21, D3D23 and D3D29; NCC 2025 Volume Two H1D8; NCC 2022 Housing Provisions Part 11.3 and Volume One D3D17 to D3D20 and D3D29; AS 1288:2021 Section 7 (clauses 7.1 to 7.4.7, pages 95 to 102). Figures verified against the ABCB's published text on 4 September 2026. Diagram by AEC Assistant. This article is general guidance; the building surveyor or certifier for your project determines compliance.
