Floor wastes are one of those jobs that look trivial and then quietly cause half the water damage claims in the country. Get the fall wrong by a whisker and you have a puddle that never leaves.
There is also a persistent myth doing the rounds about when you actually need one. Worth clearing that up first, because it changes the budget on a lot of renos.
The myth, and what the code really says
Plenty of people believe that an unenclosed or walk-in shower automatically forces you to waterproof the entire bathroom floor and add a second floor waste out in the open. That is not quite right, and the distinction is worth money.
A floor waste must be installed in the shower area, with a minimum fall to the waste of 1 in 80 and a maximum of 1 in 50 under clause 10.2.12 of the Housing Provisions. So yes, the shower needs one. That part is not optional.
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Outside the shower area is a different story. The ABCB is explicit that clause 10.2.12 is not making you install a floor waste, and notes that a floor waste may not be required outside an enclosed shower area in a Class 1 building, but if you do install one, the floor must be graded to it.
Read that twice, because it cuts both ways
You probably do not need a floor waste in the middle of the bathroom. But the moment you decide to put one in, you have signed up to grading the whole floor towards it. Plenty of renovators add a floor waste thinking it is cheap insurance, then discover the screeding bill is the expensive part.
One caveat worth naming. This is the national picture, and Queensland has its own variation on floor waste requirements. Always check your own state before you commit.
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Where the shower area actually ends
This is the bit that catches people out on open showers, and it is a hard number rather than a judgement call.
For an unenclosed shower, the shower area is the floor within a 1500mm horizontal radius of the shower rose connection, and a water stop must be placed at that 1500mm radius with the waterproofing running from the water stop back to the waste. That is the Victorian regulator's reading of the Housing Provisions, and it reflects the national clauses.
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So the shower area is defined by the rose, not by the glass. Pull the screen out and your waterproofing zone does not shrink, it becomes a 1.5 metre radius circle drawn from the rose.
Two situations where this bites unexpectedly. A shower over a bath with no screen is treated as unenclosed, so the 1500mm radius applies and will usually take in floor area outside the bath. And for a shower over a freestanding bath, any wall inside that radius without a screen has to be waterproofed to at least 1800mm up from the floor.
That last one surprises a lot of people doing the fashionable bath-in-the-shower-zone layout. The design is fine. It just quietly expands your waterproofing scope.
Getting the falls right
Falls are where good intentions go to die. The tolerance is tighter than most people assume.
|
Spec |
Number |
In plain terms |
|---|---|---|
|
Minimum fall to waste |
1 in 80 |
12.5mm drop over a metre |
|
Maximum fall to waste |
1 in 50 |
20mm drop over a metre |
|
Your working window |
Between the two |
Roughly 7mm of latitude per metre |
|
Too flat |
Under 1 in 80 |
Standing water, staining, mould |
|
Too steep |
Over 1 in 50 |
Unstable footing, rocking furniture, tile lippage |
|
Waterstop at perimeter |
Flush with finished floor |
Membrane must terminate bonded to it |
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There is a maximum for a reason. An overly steep shower floor feels wrong underfoot and looks worse, and on a linear drain it can throw the tile plane out visibly. Aim for the middle of the range rather than the minimum, because the minimum leaves you no margin for a screed that settles.
Grate choice, and why it is decided early
The grate is the only part anyone sees, and it is also the part that determines the set-out. Pick it before the screed goes down, not after.
A round chrome grate is the straightforward option, easy to set and easy to replace. Our round chrome floor grates cover the standard sizes.
A tile insert grate takes a cut piece of your floor tile so the drain nearly disappears, which is the look most people want now. The trade-off is that it demands a far more accurate set-out, because the insert has to land square with the tile grid. Our square tile insert grates are the ones to specify if that is the finish you are after.
The set-out mistake that costs a rebuild
Put the waste in the middle of a tile and you have to cut four tiles around it and the insert will never line up. Centre it on a grout junction, or set it deliberately off to one side and own the asymmetry. Decide this on paper with the tile layout in front of you, before anyone mixes screed.
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Slab versus timber floors
The two substrates behave completely differently and the job is priced differently as a result.
On a concrete slab, adding a new floor waste means cutting the slab and connecting to drainage underneath, which is why it is the expensive option and why people try to avoid it. If the slab is post-tensioned, you need engineering advice before anyone touches it with a saw, no exceptions.
On a suspended timber floor you have joists to work around and far more room to run pipework, but you also have deflection to think about. A floor that moves will crack a bonded membrane, so blocking and a rigid sheet substrate matter more than they do on a slab.
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Either way the drainage side is not a general trades job. Sanitary plumbing and drainage work is governed by AS/NZS 3500.2, and connecting to the sewer is licensed plumbing work.
Who is allowed to do what
Worth being blunt, because the paperwork is what protects you when something leaks in year four.
The Plumbing Code of Australia, NCC Volume Three, sets the requirements for plumbing and drainage installations, and the drainage connection for a floor waste sits squarely inside it.
You will need a licensed plumber, and you should expect documentation at the end. In New South Wales, for example, plumbers must provide a certificate of compliance and a sewer service diagram for notifiable work. Other states have their own equivalents. Keep whatever you are given, because it is the only evidence the work was done properly.
One more thing that gets skipped. Plumbing and drainage products that carry the WaterMark certification have been assessed as fit for purpose and authorised for use in plumbing installations. An uncertified grate or gully is a compliance problem regardless of how good it looks, so check for the mark rather than assuming.
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A sensible sequence
Order of operations matters more here than skill does.
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Settle the layout and tile grid first. The waste position follows the tiles, not the other way round.
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Confirm whether you need a waste outside the shower. Usually no, and that decision is worth real money.
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Mark the 1500mm radius if the shower is open. That is your waterproofing and waterstop line.
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Rough in the drainage. Licensed plumber, certified product, documentation at the end.
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Screed to a fall inside 1 in 80 and 1 in 50. Check it with a level and water, not by eye.
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Waterproof, with bond breakers at the junctions. Then let it cure properly before tiling.
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Tile, with the insert landing on a grout line. Dry-lay it first if you are unsure.
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The step people skip is the water test. Block the waste, flood the floor, leave it, and look underneath. Twenty minutes then beats a demolition later.
The short version
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A floor waste is required in the shower area, with falls between 1 in 80 and 1 in 50.
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A floor waste is generally not required outside the shower area in a house.
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If you do install one outside the shower, the floor must be graded to it.
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Queensland has its own variation on floor waste requirements.
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For an unenclosed shower, the shower area is a 1500mm radius from the rose connection.
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The water stop goes at that 1500mm line, flush with the finished floor.
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Waterproofing runs from the water stop back to the waste.
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A shower over a bath with no screen counts as unenclosed.
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Walls within the radius without a screen need waterproofing to 1800mm.
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Too flat means standing water, too steep feels wrong and shows in the tiles.
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Choose the grate before screeding, because it drives the set-out.
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Centre a tile insert on a grout junction, never mid-tile.
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Cutting a slab for a new waste is the expensive path, and post-tensioned slabs need engineering input.
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Drainage connection is licensed plumbing work under AS/NZS 3500.2 and the PCA.
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Use WaterMark certified products and keep the compliance paperwork.
Floor wastes reward patience at the planning stage and punish improvisation on site. If you are working out what you need for an Adelaide bathroom, come and talk it through with us, or book a showroom appointment and bring your tile layout.
