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AS 3740 vs the Housing Provisions: wet area construction compared

A house can be waterproofed to the Housing Provisions' own construction clauses or to AS 3740. They are not the same document. Pick a topic and see what each one says about the same element, with the differences flagged: the recessed leak control flange, the 25 mm step-down, hob materials, Type 1 showers, insert baths, bond breaker widths, the membrane inspection.

1Which route are you on?

Class 1 house, townhouse (NCC Volume Two)H4D2: compliance with AS 3740 or Housing Provisions Part 10.2 satisfies H4P1, provided the wet areas are protected to 10.2.1 to 10.2.6 (what must be waterproof) and the falls comply with 10.2.12 (1:80 to 1:50). So the what and the falls are fixed; the construction practice can follow the Housing Provisions 10.2.7 to 10.2.32 or AS 3740. Pick one route for the whole wet area; the differences below are what you are choosing between.
Class 2 to 9: apartments, hotels, offices, aged care (Volume One)F2D2 requires Specification 26 and AS 3740. The Housing Provisions do not apply. The AS 3740 column is your requirement; the comparison shows where a house detail would fall short of it. Check what must be waterproof.

2The comparison

Generated for indicative purposes only, not for construction. Clause text is paraphrased from the ABCB Housing Provisions (NCC 2025 Volume Two) and AS 3740:2021; read the clauses before relying on them. "Stricter" is our reading of which document asks more of the same element.

Need the wet areas designed to the right route and inspected?

Excelo designs internal waterproofing for houses and apartments, writes the specification to AS 3740 or the Housing Provisions, inspects the membrane before tiling and signs the NSW design declaration.

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Specification 26 checkerSpec 26 vs AS 3740 vs Housing ProvisionsCompliance pathway by building classDetail generator

Why two construction rule books exist

When the NCC split the house provisions out into the ABCB Housing Provisions, Part 10.2 took the wet area rules with it. Clauses 10.2.2 to 10.2.5 repeat Specification 26: what must be waterproof and what need only be water resistant. Clauses 10.2.6 to 10.2.33 then describe how to build it: materials, falls, hobs, step-downs, waterstops, flanges, flashings and doors. Clause 10.2.1(b) says a house may follow those clauses or AS 3740. Most builders and waterproofers work to AS 3740 because it is the document their training, the manufacturers' systems and the Class 2 market all use. The Housing Provisions route still exists, and a certifier can accept either.

The differences that matter on site

The floor waste. AS 3740 4.3.1 wants a leak control flange recessed into the substrate, flush, sealed to the riser and matching its diameter, and kept clear of the bond breakers. Housing Provisions 10.2.29 asks for a drainage flange with the membrane terminated at or in it, and lets it be cast in, set into the slab or set into the tile bed. A flange sitting on top of the slab under a membrane-on-screed system is acceptable under the Housing Provisions and not under AS 3740.

The step-down. Housing Provisions 10.2.15 fixes 25 mm. AS 3740 fixes nothing in general and allows 15 mm at a shower next to an exit. A 15 mm step-down on a house built to the Housing Provisions route is short.

The hob. The Housing Provisions accept masonry, concrete, AAC and extruded polyurethane foam. AS 3740 accepts masonry, concrete and corrosion-resistant metal, AAC only with an internal membrane and primed, never foam, and wants the top of the hob to fall into the shower. A foam hob former is a Housing Provisions detail.

Unenclosed showers. AS 3740 distinguishes Type 1 (a frameless panel with seals, or a 900 mm fixed panel over a bath) where the waterstop runs under the panel, from Type 2 (curtain or nothing) where it runs 1500 mm from the rose. The Housing Provisions have no Type 1: every unenclosed shower gets the 1500 mm waterstop, or the whole floor is waterproofed and drained.

Baths. Housing Provisions 10.2.20 requires every non-freestanding bath to have an upturn lip and be recessed into the wall. AS 3740 4.13 allows an insert bath without a lip provided the walls are waterproofed 150 mm above the edge, and it treats the floor around a freestanding bath as a Type 2 shower area, which the Housing Provisions do not.

Bond breakers, substrates, inspection. AS 3740 Table 4.10 fixes bond breaker widths by membrane class (100, 35 or 12 mm); the Housing Provisions only ask for compatibility. AS 3740 measures the substrate moisture content before the membrane goes down and requires a visual inspection before tiling, with an optional flood test or electronic leak detection; the Housing Provisions are silent on all three. AS 3740 accepts structural plywood as a water-resistant substrate; the Housing Provisions do not list it.

How to use the comparison

Choose the topic, or filter to "different" and "AS 3740 only" to see the gaps. Each card quotes both clauses in plain words and says which is stricter. If you are specifying a house to the Housing Provisions route, the "AS 3740 only" cards are the items you are not required to do and may want to anyway. If you are checking a Class 2 bathroom, the AS 3740 column is the requirement. For what must be waterproof in the first place, use the Specification 26 checker; for who signs what, read the compliance pathway by building class.