The Block 2025 Bathroom Week: What the Reveals Show About AS 3740 and the Housing Provisions
The Block 2025 bathroom week: adhesive failures, high vanities and an unfinished room. Every one of those maps to a clause, and the clauses for a Class 1 house are not the ones most articles cite. A verified checklist for waterproofing, ventilation, livable housing, electrical and plumbing.
The Block's 2025 bathroom week in Daylesford produced a winning room for Robby and Mat and, on the way there, tiles ripped off walls because the adhesive did not suit the substrate, vanities set too high on nearly every team, and one bathroom unfinished at tools down. For anyone who builds or certifies bathrooms for a living, the interesting part is not the drama. It is that every one of those problems is addressed by a clause, and that the clauses for a house are not the ones most articles cite.
1. What went wrong, and where the rule is
| What the reveals showed | The governing provision for a Class 1 house | What it requires |
|---|---|---|
| Tiles removed and re-laid after adhesive failed to bond | AS 3740:2021 Clause 3.2 and Clause 3.7; Appendix E | Every component of the waterproofing system, adhesive included, must be compatible with the membrane and the substrate. "Wet-area rated" on the tub is not a compatibility statement; the membrane manufacturer's tested system, or a written statement, is |
| Substrate preparation under time pressure | AS 3740:2021 Clause 4.4 | Clean, dry, smooth, free of protrusions and voids before the membrane goes on; moisture content of the subfloor tested (Appendix F) |
| Large-format, floor-to-ceiling tiling run out of time | AS 3740:2021 Clauses 4.5.2 and 4.5.3; Appendix C | The membrane must reach the overlay stage before any finish is laid and full cure before flood testing (4.5.2), and be inspected before tiling. Programme has to allow for it |
| Vanity heights judged too high | Not a code item | There is no NCC or AS 3740 vanity height for a house. The 850 to 900 mm figure is an industry convention, and the judges' complaint was ergonomic, not regulatory. Where a dwelling is designed to the Livable Housing Standard, what matters is clearances, not benchtop height |
| Open, unenclosed shower designs | Housing Provisions 10.2.18; AS 3740:2021 Clauses 2.1.1 and 4.8.2 | The waterstop sits at least 1 500 mm horizontally from the shower rose, and the floor between rose and waterstop is waterproof. AS 3740 applies the 1 500 mm to a Type 2 shower (curtain, no screen, or a screen the spray can pass); a Type 1 waterstop sits under the screen and across the opening (4.8.2) |
Two things this post used to say need correcting. NCC 2025 Volume One Specification 26 (via F2D2) applies to Class 2 to 9 buildings; a Class 1 house in Daylesford is assessed under NCC 2025 Volume Two (H4D2), which sends you to Part 10.2 of the ABCB Housing Provisions or to AS 3740, with Housing Provisions 10.2.1 to 10.2.6 and 10.2.12 applying either way. And the toilet clearances, 850 mm doors, 1 200 mm circulation and grab-rail backing that appeared in the earlier checklist are not general NCC requirements for a house. They come from the Livable Housing Design Standard, which applies to new Class 1a dwellings in Victoria, Queensland, SA, the ACT and the NT, and in Tasmania as its Director's Determination sets out, but not in NSW or WA, and with different figures from the ones we printed.
2. Class 1 bathroom checklist, with the right clauses
Verified against NCC 2025 (Volume Two, the ABCB Housing Provisions and the ABCB Livable Housing Design Standard 2025) and AS 3740:2021.
Waterproofing
| Item | Requirement | Provision |
|---|---|---|
| Shower walls | Waterproof to not less than 1 800 mm above the floor substrate | Housing Provisions 10.2.2; AS 3740 Clause 4.6.3(c) adds "or 50 mm above the rose, whichever is higher" |
| Shower floor | Waterproof, including any hob or step-down | Housing Provisions 10.2.2 |
| Floor outside the shower | Waterproof if timber; water-resistant if concrete or compressed fibre cement | Housing Provisions 10.2.3 |
| Falls to the floor waste | Floor plane between 1:80 and 1:50 to the waste | Housing Provisions 10.2.12 (AS 3740 Clause 2.3: 1:80 in the shower finish, 1:100 in the substrate and in the adjacent floor) |
| Unenclosed shower | Waterstop at least 1 500 mm from the rose; in AS 3740 that is the Type 2 rule, and a Type 1 waterstop sits under the screen (4.8.2) | Housing Provisions 10.2.18; AS 3740 Clause 4.8.2 |
| Membrane termination | 150 mm up the wall from the shower floor tiles, or 25 mm above the maximum retained water level if greater (hobbed or step-down); 150 mm above the highest floor tile (hobless); niches lined and graded 1:100 to the shower | AS 3740 Clauses 4.6.3 and 4.12.4 |
| Materials | Membrane to AS/NZS 4858; substrates from AS 3740 Clause 3.3.2; the whole system compatible | AS 3740 Clauses 3.2 and 3.3 |
| Testing | Visual inspection after cure; flood test where specified | AS 3740 Clauses 4.5.3 and 4.5.4; Appendix C |
Ventilation
| Item | Requirement | Provision |
|---|---|---|
| Exhaust rate | 25 L/s for a bathroom or sanitary compartment (40 L/s for a kitchen or laundry), for any exhaust system installed | Housing Provisions 10.8.2(1) |
| Discharge | Directly, or by shaft or duct, to outdoor air; never into the roof space | Housing Provisions 10.8.2(2) |
| Control | Where the bathroom or toilet is not naturally ventilated to 10.6.2(a), an exhaust that does not run continuously must be interlocked with the light switch and run on for 10 minutes after the light is switched off | Housing Provisions 10.8.2(4) |
| Make-up air | Where the room is not naturally ventilated to 10.6.2(a), an opening to an adjacent room with a free area of 14 000 mm² (a 20 mm undercut to a 700 mm wide door achieves it), or make-up air to AS 1668.2 | Housing Provisions 10.8.2(5) |
Livable housing (Victoria, Queensland, SA, Tasmania, ACT, NT)
| Item | Requirement | Provision |
|---|---|---|
| Doors | 820 mm clear opening to the entry-level bathroom and toilet (an 870 mm leaf usually achieves it); threshold level or ramped at 1:8 within the jamb | Livable Housing Design Standard Clauses 3.1 and 3.2 |
| Corridor to it | 1 000 mm clear between finished wall surfaces | Clause 3.3 |
| Toilet | At least one on the entry level; 900 mm between the walls of a separate compartment; fixed obstructions at least 450 mm from the pan centreline; 1 200 mm by 900 mm clear in front of the pan | Clauses 4.1 and 4.2 |
| Shower | At least one hobless, step-free shower (a 5 mm lip is allowed for water retention) | Clause 5.2 |
| Grab-rail reinforcing | 12 mm structural plywood, 25 mm timber or steel noggings in the wall zones shown in Figures 6.2a to 6.2g around the bath, shower and toilet; not needed in masonry or concrete walls | Clauses 6.1 and 6.2 |
Electrical and plumbing
| Item | Requirement | Provision |
|---|---|---|
| Wet-area zones | Fittings in the shower zones rated for the zone (IPX4 in Zone 1 as a minimum), switches outside the zones | AS/NZS 3000:2018 Section 6 (damp situations) |
| RCD protection | 30 mA RCD on the final subcircuits | AS/NZS 3000:2018 Clause 2.6.3 |
| Hot water at the outlet | Not more than 50 °C at outlets used for personal hygiene, via a thermostatic mixing valve, thermostatically controlled tap, tempering valve or temperature-limited water heater | NCC 2025 Volume Three B2D5 and B2D6 (a lower 45 °C limit applies in some other building types; NSW, SA and WA vary B2D5) |
| Flexible hoses (2025 editions) | Class 2 or 3 hoses between fixed points, an isolating valve immediately before each hose | AS/NZS 3500.1:2025 Clauses 2.3.2 and 5.4.2; AS/NZS 3500.4:2025 Clause 10.10.2 |
| Backflow | Backflow prevention appropriate to the hazard rating | AS/NZS 3500.1 Section 4 |
Approvals and evidence
A building permit where the work is structural or creates a new wet area; check the local threshold. In Victoria, a registered building practitioner and a building surveyor for work above the domestic building contract threshold.
Plumbing work by a licensed plumber, with a compliance certificate where the state requires one (Victoria: for most sanitary and water-supply work).
Electrical work by a licensed electrician with a certificate of electrical safety.
A waterproofing certificate from the installer, naming the membrane system and the standard, before tiling. Photograph the membrane, the waterstops and the flanges before they are covered.
Manufacturer compatibility statements for every substitution in the waterproofing system, kept with the certificate.
3. What the show gets right
Waterproofing is the trade that cannot be checked after the tiles go on, and The Block films the stage that is normally invisible. The teams that had to strip tiles were not failing an obscure rule. They were skipping the compatibility check that AS 3740 puts in Clause 3.2, one sentence long, and the programme time that curing needs: the overlay stage before tiling and full cure before any flood test (Clause 4.5.2). On a real job those are the two items that separate a bathroom from a defect claim within the warranty period.
Sources: NCC 2025 Volume One F2D2 and Specification 26; NCC 2025 Volume Two H4D2 and H4D3; ABCB Housing Provisions Standard 2025, Parts 10.2 and 10.8; NCC 2025 Volume Three B2D5 and B2D6; AS 3740:2021; ABCB Livable Housing Design Standard 2025 and the state adoption information published by the ABCB; AS/NZS 3500.1 and 3500.4:2025; AS/NZS 3000:2018. The Block details are as broadcast by the Nine Network in Week 1 of the 2025 season. First published 4 August 2025; rewritten 2 September 2026 with the checklist re-attributed to the provisions that apply to a Class 1 house; updated 28 September 2026 to cite NCC 2025.
Questions this guide answers
Why did tiles fail on The Block 2025 bathrooms?
The adhesive did not suit the substrate. AS 3740:2021 Clause 3.2 and Appendix E require every component of the waterproofing system, adhesive included, to be compatible with the membrane and the substrate; "wet-area rated" on the tub is not a compatibility statement.
Is there an NCC vanity height for a house?
No. There is no NCC or AS 3740 vanity height for a house; the 850 to 900 mm figure is an industry convention, and the judges' complaint was ergonomic, not regulatory.
Which code applies to a Class 1 house bathroom?
A Class 1 house is assessed under NCC 2025 Volume Two (H4D2 and H4D3), which sends you to Part 10.2 of the ABCB Housing Provisions or to AS 3740. Volume One Specification 26, called up by F2D2, applies to Class 2 to 9 buildings.
