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Guide 2 of 5 · the bathroom floor

The waterproofing comes first on a bathroom floor

On a tiled bathroom floor the treatment comes first, then the tiles. In NSW you must have a licence or certificate to do waterproofing work.

The rules below are the National Construction Code 2025's wet-area provisions, clause by clause, and the NSW licence pages. The clause numbers are the code's own.

Bathroom Tiles Waterproofing is trade work; a licence or certificate (NSW) Living room Boards Changing the floor in an apartment needs permission (NSW) Laundry Vinyl, flat tone Old backing: friable, for a licensed removalist (VIC, SA) Bedroom Boards over a subfloor Insulation and ventilation under the floor Hall Carpet Licence lines for floor work differ by state (QLD, NSW, VIC)
Not to scale.
  1. Living room · Boards Changing the floor in an apartment needs permission (NSW) Open the living room guide
  2. Hall · Carpet Licence lines for floor work differ by state (QLD, NSW, VIC) Open the hall guide
  3. Bedroom · Boards over a subfloor Insulation and ventilation under the floor Open the bedroom guide
  4. Bathroom · Tiles Waterproofing is trade work; a licence or certificate (NSW) Open the bathroom guide
  5. Laundry · Vinyl, flat tone Old backing: friable, for a licensed removalist (VIC, SA) Open the laundry guide

The rooms in the order they run through the house, from the front door to the back.

What waterproofing work is

NSW defines the work before it licenses it. Waterproofing is any protective treatment of a home to prevent water or moisture getting into it.

It is also the protective treatment of wet areas of a home, such as a shower, to stop the unwanted escape of water from those areas.

The treatment itself is a membrane: solid membranes, or membranes applied by brush, roller or any other method.

The tiling page describes the same step from the other side of it. Wall and floor tiling work and materials can include waterproofing wet areas to get them ready for tiling.

The State points to the full definition in schedule 4 of the Home Building Regulation 2014. The work is trade work.

The code's wet-area clauses

The code sets its wet-area rules as numbered clauses. A selection follows, each close to the code's wording.

  1. The falls in the floor. Where a floor waste is installed, the minimum continuous fall of a floor plane to the waste must be 1:80.
  2. The maximum fall. Where a floor waste is installed, the maximum continuous fall of a floor plane to the waste must be 1:50.
  3. The floor's own level of treatment. For concrete, compressed fibre-cement and fibre-cement sheet flooring, the floor of the room must be water resistant.
  4. The same, on timber. For timber floors, including particleboard, plywood and other timber based flooring materials, the floor of the room must be waterproof.
  5. The shower walls. For hobless showers, or showers with hobs or stepdowns, the membrane must be applied over the floor and up the vertical face of the wall substrate.
  6. How high the membrane goes. The wall substrate is treated to a minimum height of 1800 mm above the finished tile level of the floor. Penetrations within the shower area must be waterproof.
  7. The junctions. Bond breakers must be installed at all wall to wall, wall to floor and hob to wall junctions, and at movement joints where the membrane is bonded to the substrate.
  8. The stepdown. For stepdown showers, the highest finished floor level of the shower area must be stepped down a minimum of 25 mm lower than the finished floor level outside the shower.
  9. The hob. Where a shower has a hob, the membrane must be brought over the top of the hob and down the outside face.
  10. Where the membrane stops. It must terminate not less than 50 mm onto the floor, and timber must not be used for hob construction.
  11. The waste. Shower areas must incorporate a floor waste with falls complying with the falls clause, and the waste must suit the thickness of the tile and tile bed at the outlet position.
  12. Above or below the screed. Where a screed is used in conjunction with a waterproof membrane, the membrane can be installed either above or below the tile bed or screed.
  13. Penetrations in horizontal surfaces. Tap and spout penetrations must be waterproof where they occur in horizontal surfaces.
  14. The door jamb. Where the bottom of a door jamb does not finish above the floor tiling, the portion of the door frame below it must be waterproofed.
  15. What that seal joins. The waterproofing below the tiling provides a continuous seal between the perimeter flashing and the waterstop. An unenclosed shower needs its own waterstop, at a minimum horizontal distance of 1500 mm from the shower rose.
  16. The rest of the room. Outside the shower area, a concrete, compressed fibre-cement or fibre-cement sheet floor must be water resistant, and a timber floor must be waterproof. Wall and floor junctions must be waterproof.
  17. The flashing beside the junction. Where a flashing is used, its horizontal leg must be not less than 40 mm.
  18. The materials and the system. A waterproofing system required to be waterproof must use the materials the code nominates for it, including membranes complying with AS/NZS 4858.
  19. The other level's materials. A system required to be water resistant must use the materials nominated for that level, together with the surface materials that go with them.
  20. One worked example. The code names sheet vinyl or linoleum as a material that would satisfy the water-resistant requirements of this clause.
  21. Then the tiles. NSW's tiling page counts waterproofing wet areas to get them ready for tiling as part of wall and floor tiling work.

The two levels the code uses

The clauses above use two levels, waterproof and water resistant.

The code asks for waterproof in the shower area, on timber floors in the room, and at the wall and floor junctions outside the shower. It asks for water resistant on concrete and fibre-cement floors outside the shower area.

The levels decide which materials a system may use, so they are worth reading twice. A system that must be waterproof takes membranes complying with AS/NZS 4858.

A system that must be water resistant takes its own nominated materials together with the surface materials. Sheet vinyl or linoleum is named as one that would satisfy it.

Who may do the work in NSW

NSW's page for waterproofing work states it: a licence or certificate is required for waterproofing work, and an applicant needs the required qualifications and experience before applying. The page lists the qualifications to complete.

The money threshold comes with the licence, on the same page: a contractor licence is needed for residential building or trade work valued at more than $5000 in labour and materials, including GST.

Waterproofing is named among that work, which brings the licence to the wet-area floor.

The same page adds the terms of it: a licence or certificate runs for one, three or five years.

Your Home’s Minor home upgrades page writes for the householder. Waterproofing should be done by a professional, and the same page says you will need licensed experts for electrical, plumbing or waterproofing work and, as a rule of thumb, that where work must be certified for safety, health or compliance with regulations, licensed professionals must be used, waterproofing included.

The reason it gives is the cost of getting it wrong: waterproofing failures are among the most expensive building defects in Australia.

When the job brings approval with it

A bathroom is small, but the work in it can cross into approvals. Your Home's page for home upgrades says changes to services often require building approval as part of larger building work.

The services it names are plumbing, drainage, gas and electrical.

The examples the page gives are the ones a wet room meets: work requiring cutting through floors, or waterproofing.

Your Home puts the bathroom case directly: minor bathroom renovations will still need approval if there is waterproofing work required or there are changes to plumbing layouts.

Its advice on where to take the question is local: the best option is to check with your local council.

The licence for the floor itself is another guide on this plan: who may lay a floor, state by state, and the permission a floor over a neighbour's ceiling needs is hard floors in a strata apartment.