Floor fall is one of those details that nobody thinks about until their shower floor holds a puddle after every wash. Get it right and you never notice it, water simply disappears down the waste. Get it wrong and you have pooling, slow drainage, mould in the low spots, and over time water working its way past the seals it should never reach. The fall is the unglamorous engineering that makes a bathroom actually function, and it is set in the screed long before the pretty tiles go on.
What "fall" means in plain terms
Fall is just slope. A fall of 1:60 means the floor drops 1 unit for every 60 units of horizontal distance, so roughly 16mm of drop over a metre. A fall of 1:80 is gentler, about 12mm of drop over a metre. The floor is built to tilt gently toward the floor waste so gravity carries the water to the drain. That is the whole idea, you are building a very shallow funnel that you happen to be able to stand on.
The numbers we work to
Falls and bathroom drainage are governed by AS 3500, the standard for plumbing and drainage. As a practical guide for a Gold Coast bathroom:
- The general bathroom floor typically falls to the floor waste at around 1:60 to 1:80. That is roughly 12mm to 16mm of drop per metre toward the drain.
- The shower area itself is usually set a touch steeper than the main floor, so the area that gets the most water clears it quickly and never holds a puddle.
- The fall has to be consistent all the way to the waste, with no flat spots or low pockets where water can sit.
These are guide figures, not a substitute for the standard. The exact fall for your room depends on the layout, the distance from the far corner to the waste, the tile size and the type of drain. What does not change is the principle, every point on a wet floor has to drain to the waste, with no flat spot left behind.
Why too flat is a problem
If the fall is too gentle, or worse, if there is a dead-flat patch or a slight back-fall away from the waste, water pools. Pooling causes a chain of problems, mould and discolouration in the low spots, soap and mineral residue building up, grout staying wet and breaking down faster, and over the long run water sitting on the membrane and probing for the weakest seal instead of draining away. A flat shower floor is one of the most common reno complaints we get called to, and because the fall lives in the screed, it is never a surface fix. We dig into the leak side of this in what causes bathroom leaks after a renovation.
Why too steep is also a problem
You cannot just crank the fall up to be safe. Too much fall and the floor feels wrong underfoot, you can feel yourself standing on a slope, a freestanding shower screen or a frameless panel can sit oddly, and large tiles start to look visibly tilted. There is also a practical limit, a steep floor forces awkward cuts and lippage on big tiles. The skill is setting enough fall to drain reliably without the floor feeling like a ramp. That balance is exactly why this is screeded by someone who has done it many times, not eyeballed.
How tile size changes the picture
This is the part homeowners often miss. The bigger the tile, the harder it is to build fall into the floor, because a large rigid tile cannot bend to follow a slope that runs in two directions at once. A small mosaic tile can follow a floor that falls toward a central waste from every direction, all those little grout joints let the tile bed curve. A big-format tile cannot do that, it wants to fall in a single direction along a single plane.
That is the whole reason large-format tiles and linear drains go together. A linear drain lets the entire shower floor fall in one direction toward a strip at one edge, so a big tile can sit on a single clean plane. Trying to run big tiles to a central square waste means the floor has to fall from four directions toward one point, which forces the tiles into a shallow dish shape they are not happy in. We compare the two approaches in linear drain vs standard floor waste.
Centre waste vs linear drain, in fall terms
Standard centre or square waste
With a traditional floor waste in the middle of the shower, the floor has to fall toward that single point from all four sides. You are effectively building a very shallow inverted pyramid. It works well with smaller tiles whose many grout lines can follow the compound slope, and it is the long-proven, cost-effective approach. With large tiles it gets fiddly fast.
Linear drain
A linear drain is a long, narrow channel, usually set against one wall or at the shower entry. Because all the water heads to a line rather than a point, the floor only has to fall in one direction. That single-plane fall is what makes large-format tiles practical in a shower, and it is the main reason linear drains have taken over premium Gold Coast bathrooms. The tradeoff is cost and getting the channel set dead level along its length, the fall runs to the channel, but the channel itself sits flat.
Why it has to be set before tiling
This is the point worth hammering. The fall is created in the screed bed under the tiles. Once the waterproofing is on and the tiles are laid, the slope is locked in. There is no adjusting it afterwards short of lifting the floor, ripping out the screed, and starting that part again, which means new waterproofing and new tiles. A floor that drains badly is not a tweak, it is a redo. That is why we set and check the falls carefully at the screeding stage, and why the falls and the waterproofing are checked together, water only drains if the floor sends it to the waste, and the membrane only protects you if the water is leaving. They are two halves of the same job, which is also why both should be documented, see do I need a waterproofing certificate.
How we get it right
- We plan the waste type and tile size together, because they decide which way the floor falls.
- We set the screed to consistent fall toward the waste, with no flat spots, and a slightly steeper fall in the shower zone.
- We check the fall with water before the membrane goes on, the floor should drain clean with no puddle left behind.
- We match the drain to the design, a linear drain for single-direction fall with big tiles, a centre waste where smaller tiles and budget suit.
What it costs
Setting the falls is part of the screeding and waterproofing scope rather than a standalone line, and the cost moves with the size of the room, the tile choice and the drain type. A linear drain setup generally costs more than a standard centre waste, both for the drain itself and the tiling work around it. As always, the honest number comes from a quote on your actual bathroom, not a guess over the phone.
The falls are invisible when the job is done well and impossible to ignore when it is done badly. If your shower pools, or you are planning a reno with big tiles and want it to drain properly the first time, take a look at our bathroom renovations service or read the full bathroom renovation plumbing guide. To get your room set up right, get in touch.