Which part of the NCC covers waterproofing in an apartment bathroom?

NCC Volume One. F2D2(1) requires building elements in the wet areas of Class 2 and 3 buildings and Class 4 parts to be water resistant or waterproof in accordance with Specification 26 and to comply with AS 3740. F2D4 requires a floor waste in a bathroom or laundry above another sole-occupancy unit or public space, and S26C6(4) then makes that floor waterproof.

Can a house be waterproofed without AS 3740?

Yes. Volume Two H4D2 accepts either AS 3740 or Part 10.2 of the ABCB Housing Provisions, provided the wet areas are protected to Housing Provisions 10.2.1 to 10.2.6 and the falls comply with 10.2.12. So the what (waterproof or water resistant) and the falls are fixed; the how can follow either rule book.

When do I need a Performance Solution for internal waterproofing?

Whenever the design departs from the Deemed-to-Satisfy provisions: a window inside a shower area, a level entry with no waterstop, an unenclosed shower within 200 mm of the door, a membrane omitted under a tiled floor over another occupancy, a hob of a material not listed. The Performance Solution demonstrates compliance with F2P2 (Volume One) or H4P1 (Volume Two) by one of the A2G2 assessment methods, usually expert judgement and comparison with the Deemed-to-Satisfy provisions.

Who has to declare the waterproofing design in NSW?

For Class 2 buildings (since 1 July 2021) and Class 3 and 9c buildings (since 1 July 2023), waterproofing is a regulated design under the NSW Design and Building Practitioners Act. A registered design practitioner lodges the design and a design compliance declaration before the work starts, and the building practitioner declares that the work was built to it. Houses and most Class 5 to 9 buildings are outside the scheme, although the certifier still asks for evidence of suitability.

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Internal waterproofing compliance pathways by building class

Published 18 October 2026. Which NCC volume governs the wet areas of your building, which Deemed-to-Satisfy route applies, when a floor waste is mandatory, when you need a Performance Solution, and who signs what in NSW. NCC 2025 clause numbers; NCC 2022 applies in NSW until 1 May 2027 and the numbering is the same.

The first question a certifier asks about a wet area is not "is it waterproofed?" but "to what?". The answer depends on the class of the building, because the NCC splits internal waterproofing between two volumes with different structures, and New South Wales adds a declaration regime on top for some classes. This article sets out the pathway for each class, with the matrix at the end.

Check what must be waterproof → Compare the two house routes →

In this article The building classes, in one paragraph Class 1 and 10: Volume Two, two routes Class 2, 3 and 4 parts: Volume One, one route, plus the floor waste rule Class 5 to 9: Volume One, as if Class 2 When the Deemed-to-Satisfy route runs out: Performance Solutions New South Wales: who declares what What the certifier will ask for The matrix

The building classes, in one paragraph

Class 1 is a house or townhouse (1a) or a small boarding house (1b). Class 2 is a building with two or more sole-occupancy units, each a separate dwelling: apartments. Class 3 is residential accommodation for unrelated people: hotels, hostels, backpackers, the residential part of a school. Class 4 is the single dwelling inside a non-residential building: the caretaker's flat. Class 5 is offices, 6 shops and restaurants, 7 car parks and warehouses, 8 factories, 9 public buildings including health care (9a), assembly (9b) and aged care (9c). Class 10 is non-habitable: sheds, garages, pool houses. Class 1 and 10 live in Volume Two; everything else in Volume One.

Class 1 and 10: Volume Two, two routes

Deemed-to-Satisfy: H4D2 and H4D3Compliance with AS 3740 or Part 10.2 of the ABCB Housing Provisions satisfies Performance Requirement H4P1, provided the wet areas are protected to Housing Provisions 10.2.1 to 10.2.6 and the floor falls comply with 10.2.12.

Read that proviso carefully. Whichever route the builder takes, two things are fixed by the Housing Provisions: what must be waterproof or water resistant (10.2.2 to 10.2.5, the same words as Specification 26, with 10.2.1(d) adding that a floor drained by a floor waste is waterproof) and the falls to any floor waste (10.2.12: 1:80 minimum, 1:50 maximum). Only the construction practice is a choice: the Housing Provisions' own clauses 10.2.7 to 10.2.32, or AS 3740:2021 Sections 2 to 4.

The two construction rule books differ in ways that show up on site: the Housing Provisions want a 25 mm step-down and a lip on every non-freestanding bath, and accept a polyurethane foam hob; AS 3740 wants the leak control flange recessed, fixes bond breaker widths by membrane class, measures the substrate moisture, allows insert baths without a lip and a Type 1 unenclosed shower with a smaller waterstop, and requires a membrane inspection before tiling. Pick one route for the whole wet area and say which on the drawings; mixing them is how a job ends up compliant with neither. The full comparison is in the AS 3740 vs Housing Provisions tool.

A floor waste is not mandatory in a house bathroom outside South Australia (SA 10.2.33). If one is provided, 10.2.1(d) makes the floor waterproof and 10.2.12 fixes its falls. A shower area always has one (10.2.14(2)).

Check a house bathroom with a floor waste →

Class 2, 3 and 4 parts: Volume One, one route, plus the floor waste rule

Deemed-to-Satisfy: F2D2(1)Building elements in wet areas must be water resistant or waterproof in accordance with Specification 26, and comply with AS 3740. No alternative construction route.

Apartments, hotels and the caretaker's flat have no choice of rule book: Specification 26 says what, AS 3740 says how, and both apply. Then the floor waste rule bites. F2D4(1) requires a floor waste in any bathroom or laundry located above another sole-occupancy unit or a public space, and F2D4(2) fixes the fall to it between 1:80 and 1:50. Because the waste is required, S26C6(4) makes the whole floor of that room waterproof, together with its wall/floor junctions and its floor penetrations, whatever the substrate. A ground-floor apartment bathroom over a car park is "above a public space"; an apartment bathroom over another apartment is the common case. In practice every Class 2 wet area above ground gets a fully waterproofed floor, and our specification uses a dual membrane for it.

The shower is governed by S26C3 (floor, walls to 1800 above the substrate, junctions, penetrations), baths by S26C5, basins and WCs by S26C6, and AS 3740 supplies the shower types, the 1500 mm Type 2 extent, waterstops, hobs, terminations and the inspection.

Check a Class 2 bathroom above another unit → The same bathroom on the ground floor →

Class 5 to 9: Volume One, as if Class 2

Deemed-to-Satisfy: F2D2(2)In a Class 5, 6, 7, 8 or 9 building, building elements in a bathroom or shower room, a slop hopper or sink compartment, a laundry or a sanitary compartment must be water resistant or waterproof in accordance with Specification 26 and comply with AS 3740, as if they were in a Class 2 or 3 building.

So the office end-of-trip showers, the hospital ensuites, the aged care bathrooms and the restaurant WCs follow exactly the Class 2 reading of Specification 26 and AS 3740. The difference is the floor waste: F2D4(1) names only Class 2 and 3 buildings and Class 4 parts, so a Class 5 to 9 wet area is not required to have a floor waste by that clause, and a floor waste that is merely provided does not trigger S26C6(4). The floor outside the shower of a concrete-floored office shower room is water resistant under S26C4(1). Health care and aged care bring their own rules: F2D3 for rooms with urinals, and in Class 9c the usual expectation of fully waterproofed floors in resident bathrooms, which we specify regardless of the minimum.

Check a commercial shower room →

When the Deemed-to-Satisfy route runs out: Performance Solutions

The Deemed-to-Satisfy provisions describe a conventional bathroom. The moment the design leaves it, the pathway changes from "comply with the clause" to "demonstrate compliance with the Performance Requirement": F2P2 in Volume One, H4P1 in Volume Two. Both say the same thing: water must be prevented from penetrating behind fittings and linings and into concealed spaces of sanitary compartments, bathrooms, laundries and the like.

The triggers we see most:

A window inside the shower area, where the wall membrane cannot run across a frame.
A level, hobless entry with no waterstop at the shower, or a whole-floor shower with the waterstop at the door.
An unenclosed shower within 200 mm of the exit (AS 3740 4.8.5 says enclosed).
A membrane omitted under a tiled floor over another occupancy, relying on the slab.
A hob, base or lining of a material neither rule book lists.

A Performance Solution under A2G2 states the Performance Requirement, the assessment method (for wet areas almost always expert judgement with a comparison against the Deemed-to-Satisfy provisions), the acceptance criteria and the evidence, and it is signed by someone qualified to judge it. In NSW that person is a registered design practitioner where the DBP Act applies. Our waterproofing Performance Solutions page sets out the cases and what the report contains.

New South Wales: who declares what

The Design and Building Practitioners Act 2020 adds a layer above the NCC for some classes. Waterproofing is a regulated design for Class 2 buildings (since 1 July 2021) and for Class 3 and 9c buildings (since 1 July 2023), including mixed-use buildings with those parts. For those buildings a registered design practitioner prepares the waterproofing design and lodges a design compliance declaration before the work starts; the registered building practitioner then declares that the building work complies with the declared design, and any variation needs a varied design. The declaration covers the Deemed-to-Satisfy route and any Performance Solution alike. Houses, Class 4 parts of other buildings and Class 5 to 9 buildings outside 9c sit outside the scheme, which does not relieve them of the NCC: the certifier still needs evidence that the wet areas comply. Our guide to DBP Act declaration thresholds covers the detail, and the process of waterproofing a Class 2 building walks through a declared job.

What the certifier will ask for

The route, named. Volume One: Specification 26 + AS 3740. Volume Two: Housing Provisions 10.2 with the construction route stated (10.2.7 to 10.2.32 or AS 3740).
The extent drawings. Which floors, walls and junctions are waterproof and which water resistant, with the 1800 shower height, bath and basin bands and the unenclosed shower extent marked. The Specification 26 checker produces the list.
The details. Floor/wall junction, threshold, floor waste, screen waterstop or hob, bath junction, penetrations, drawn for the actual build-up. The detail generator gives the generic starting set.
Evidence of suitability (A5G3) for the system: membranes to AS/NZS 4858, the manufacturer's system and compatibility, WaterMark on the floor waste and flanges.
The membrane inspection before tiling, required by AS 3740 4.5.3, with a flood test or electronic leak detection where specified.
In NSW, for Class 2, 3 and 9c: the lodged design, the design compliance declaration and the building compliance declaration.

The matrix

Class	NCC volume and DtS clause	What must be waterproof	Construction practice	Floor waste	Performance Requirement	NSW DBP declaration
Class 1a, 1b	Volume TwoH4D2, H4D3	Housing Provisions 10.2.1 to 10.2.6 (same words as Spec 26; floor waterproof wherever a waste drains it)10.2.1(d)	Housing Provisions 10.2.7 to 10.2.32 or AS 3740:2021; falls 1:80 to 1:50 either way10.2.1(b), 10.2.12	Not required except SA; always in a shower areaSA 10.2.33, 10.2.14(2)	H4P1	No
Class 10a, 10b	Volume TwoH4D2	As Class 1 where a wet area exists (pool house bathroom, laundry in a garage)	As Class 1	As Class 1	H4P1	No
Class 2	Volume OneF2D2(1)	Specification 26S26C3 to S26C6	AS 3740:2021, no alternative	Required above another unit or public space; floor then waterproof; falls 1:80 to 1:50F2D4, S26C6(4)	F2P2	Yes, since 1 July 2021: design declaration + building declaration
Class 3	Volume OneF2D2(1)	Specification 26	AS 3740:2021	As Class 2F2D4	F2P2	Yes, since 1 July 2023
Class 4 part	Volume OneF2D2(1)	Specification 26	AS 3740:2021	As Class 2F2D4	F2P2	Only if the building is a Class 2, 3 or 9c building
Class 5, 6, 7, 8	Volume OneF2D2(2)	Specification 26, as if Class 2	AS 3740:2021	Not required by F2D4; a provided waste does not trigger S26C6(4)	F2P2	No (unless part of a mixed Class 2, 3 or 9c building)
Class 9a, 9b	Volume OneF2D2(2), F2D3	Specification 26, as if Class 2; urinal rooms per F2D3	AS 3740:2021	Not required by F2D4	F2P2	No
Class 9c	Volume OneF2D2(2)	Specification 26, as if Class 2	AS 3740:2021	Not required by F2D4 (clinical basins excepted)	F2P2	Yes, since 1 July 2023

Where the Deemed-to-Satisfy route cannot be met in any class, the pathway is a Performance Solution against the Performance Requirement in the sixth column, assessed under A2G2.

Need the pathway sorted for your building, the wet areas designed and the NSW declaration signed? Talk to our waterproofing engineers. We work across Class 1 houses, Class 2 and 3 apartments and hotels, and Class 9 health and aged care.