AS 3740:2021 Explained: Scope, Changes from 2010, and How the NCC Calls It Up

AS 3740:2021 Waterproofing of domestic wet areas is the edition NCC 2025 calls up in its wet-area provisions (Schedule 2: Volume One F2D2; Volume Two H4D2 and H4D3; Housing Provisions 10.2.20). It replaced the 2010 edition in 2021. This guide is for the people who specify, install and certify against it. It explains what the standard covers, what changed from 2010 with clause references, which NCC clause calls it up for your building class, and the numbers you need at hand.

1. Scope

AS 3740:2021 sets minimum requirements for the materials, design and installation of waterproofing. It applies to internal wet areas in domestic buildings as defined by the NCC: bathrooms, ensuites, laundries and areas with a basin or a floor waste.

It does not cover:

• Flooding from plumbing failure or overflowing vessels.

• Concrete admixtures or penetrant sealers used alone.

• Purely decorative coatings.

• Communal wet areas such as pool changerooms.

The standard is organised in four sections plus six appendices. The sections are Section 1 Scope and general, Section 2 Design, Section 3 Materials and Section 4 Installation. The appendices are Appendix A (design considerations and risk categories), B (falls in floor finishes), C (membrane continuity testing, normative), D (a suggested installation checklist), E (compatibility) and F (moisture testing of subfloors).

2. How the NCC calls it up

Building class	NCC 2025
Class 1 houses and Class 10	Volume Two H4D2 and H4D3: waterproof or water resistant to Housing Provisions 10.2.1 to 10.2.6, then either AS 3740 plus 10.2.12, or the self-contained provisions in 10.2.7 to 10.2.32 (South Australia's variation of 10.2.1 names AS 3740 directly)
Class 2 to 9	Volume One F2D2: waterproof or water resistant to Specification 26 and complying with AS 3740 (F2D2(1) for Class 2 and 3 buildings and Class 4 parts; F2D2(2) for bathrooms, laundries and sanitary compartments in Class 5 to 9). The rewritten Part F1 deals with external membranes, roofs and podiums, not internal wet areas

This has two consequences. First, the standard's details apply to a Class 2 apartment bathroom too. That bathroom is not "domestic" for the purposes of the standard's own scope, but F2D2 sends you to AS 3740 for installation. Second, the NCC schedule of referenced documents fixes the edition. A specification that says "AS 3740-2010" on a project assessed under NCC 2025 is citing a superseded document.

3. What changed from AS 3740:2010

The preface lists nine changes. In practice they come down to these:

Change	Where	Why it matters on site
Three risk categories for wet areas	Appendix A.3; used throughout Section 2	Category 1 (shower areas and baths with unenclosed showers) is high risk and water must be retained inside it; Category 2 is the whole bathroom outside an unenclosed shower (A.3.3); Category 3 is the bathroom outside an enclosed shower, or a wet area with no shower (A.3.4)
Shower classification: enclosed, unenclosed Type 1, unenclosed Type 2	Clause 2.2	Frameless screens are Type 1 unless fitted with seals and deflectors that control the spread of water (2.2.2.1(a)(i)); curtains, no screen, and screens the spray can pass are Type 2. The type drives the waterstop and extent-of-waterproofing rules
Falls stated per category	Clause 2.3	Substrate under the membrane 1:100 minimum where there is a floor waste (2.3.1); shower floor finish 1:80 minimum (2.3.2); Category 2 floor finish 1:100 minimum (2.3.3); a whole bathroom designed as an unenclosed shower needs 1:80 in the substrate (2.3.5)
Unenclosed showers: 1 500 mm extent	Clauses 2.1.1 and 4.8.2	Waterproofing extends at least 1 500 mm from the substrate connection of the shower rose (2.1.1). A Type 2 waterstop sits at least 1 500 mm from the rose (4.8.2(b)); a Type 1 waterstop sits under the splash restriction device and across the opening (4.8.2(a))
Vertical membrane termination	Clause 4.6.3	Shower walls: 1 800 mm above finished floor or 50 mm above the rose, whichever is higher; full height where the rose is ceiling mounted. Hobbed or stepped showers: 150 mm above the finished tile level of the floor or 25 mm above the maximum retained water level, whichever is the greater (4.6.3(a)). Hobless: 150 mm above the highest finished floor in the shower
Hobless and step-down showers detailed	Clauses 4.8.3 to 4.8.5, 4.15; Figures 4.8.2 and 4.8.4	A step-down of at least 15 mm where the shower is within 200 mm of an exit (4.8.5(b)(iii)), or a waterstop finishing at least 5 mm above the outer floor (4.8.4); screen placement rules for each case
Linear drains	Clause 4.3.2; Appendix A.6	Connection details for channel drains and four whole-of-bathroom design solutions with linear drains
Niches	Clause 4.12.4; Figure 4.12.4	Lined on all faces with a water-resistant substrate, fillets or bond breakers at every junction, base graded at least 1:100 towards the shower
Hob construction	Clause 4.7	Hob top falls towards the shower; no timber hobs; joints made flush before the membrane goes on
Membrane inspection and continuity testing	Clauses 4.5.3 and 4.5.4; Appendix C (normative)	Visual inspection before any finish is laid; flood testing to C.2 only after full cure, with the shower and the outer floor tested separately where a hob or waterstop divides them
Compatibility as a system	Clause 3.2; Appendix E	Every component from primer to grout must be compatible with the membrane; the "compatibility chain" in Figure E.1 is the checklist
Moisture in subfloors	Clause 4.4.3; Appendix F	A test method for deciding whether a concrete or timber subfloor is dry enough for the membrane

4. Materials: waterproof or water-resistant

Section 3 sorts materials into two groups. Materials deemed waterproof stand alone (Clause 3.3.1). They are:

• Stainless steel.

• 99.9% copper to AS 1566.

• Flexible sheet flooring with sealed and welded joints meeting AS/NZS 4858.

• Wet-area membranes meeting AS/NZS 4858.

• Glass to AS 1288.

• PVC to AS/NZS 3500.2.

Everything else in a wet area is at best water-resistant (Clauses 3.3.2 and 3.3.3). Wherever the NCC requires a waterproof element, a water-resistant material needs a waterproof layer somewhere in the build-up. Our companion article on waterproof versus water-resistant materials works through the lists and the compatibility chain.

5. The numbers to keep at hand

Item	Requirement	Clause
Shower wall waterproofing height	1 800 mm above finished floor, or 50 mm above the rose, whichever is higher	4.6.3(c)
Unenclosed shower extent	1 500 mm from the rose connection	2.1.1, 4.8.2
Fall in shower floor finish	1:80 minimum	2.3.2
Fall in substrate to floor waste	1:100 minimum	2.3.1
Fall in Category 2 floor finish	1:100 minimum	2.3.3
Step-down at shower extremity	15 mm minimum where the shower is within 200 mm of an exit	4.8.5(b)(iii)
Membrane up wall, hobbed or stepped shower	150 mm above the finished tile level or 25 mm above the maximum retained water level, whichever is the greater	4.6.3(a)
Niche base fall	1:100 towards the shower	4.12.4
Bath walls (shower over bath)	Waterproof to 150 mm above the bath edge; junctions and penetrations to 1 800 mm above the bath floor	4.13.3

The Housing Provisions carry their own figures for a Class 1 house, and they are not identical. The floor plane must fall to the waste at between 1:80 and 1:50 (10.2.12). Shower walls must be waterproof to not less than 1 800 mm above the floor substrate (10.2.2). For a Class 1 house these apply on both routes: NCC 2025 Volume Two H4D3 requires Housing Provisions 10.2.1 to 10.2.6 in every case and adds 10.2.12 to the AS 3740 route, so the falls must sit between 1:80 and 1:50 even where the rest of the detail follows AS 3740.

6. Common errors the standard was written to stop

• Membrane over a substrate with no fall, so water ponds under the tiles even though the tile surface drains (Clause 2.3.1).

• A 1 800 mm wall height measured from the tile bed rather than finished floor, or ignored where a rain-head sits higher (4.6.3).

• Type 2 unenclosed showers with the waterstop at the screen line instead of 1 500 mm from the rose (4.8.2(b)).

• Tiling before the membrane has cured, then flood testing a wet membrane (4.5.2, C.2).

• A primer, bond breaker or tile adhesive from a different system to the membrane, with no compatibility statement (3.2, Appendix E).

7. Who may do the work

The standard is silent on who holds the trowel, but the state licensing regimes are not. Queensland and New South Wales license waterproofing as a trade in its own right. Other states regulate it through the builder's registration and the inspection regime. A waterproofing certificate from the installer, naming the system and the standard, is routine evidence at the pre-tiling inspection. It is worth specifying on every job.

Sources: AS 3740:2021 (Standards Australia), preface, Sections 2 to 4 and Appendices A, C, E and F. NCC 2025 Volume One F2D2, Specification 26, Part F1 and Schedule 2; NCC 2025 Volume Two H4D2 and H4D3; ABCB Housing Provisions Standard 2025, Part 10.2. Figures A.6(A) and A.6(B) reproduced for review and commentary. First published 1 September 2026; rewritten with clause references 2 September 2026; updated 28 September 2026 to cite NCC 2025.