Wet room knowledge — floor build-up
A wet room floor has to do something an ordinary bathroom floor never does: drain itself. There is no tray to catch the water, so the floor is built with a gentle slope — the fall, or gradient — that carries every drop to the drain and leaves the surface dry. Get the fall right and you never notice it underfoot; get it wrong and you either stand in puddles or feel like you’re on a hillside. This guide explains what a fall is, the two ways we form one in Plymouth homes, the figures we work to, and why the falls always go in before the waterproofing.
What a “fall” is and why it matters
A fall is simply a controlled slope built into the floor so that water runs toward the drain rather than sitting where it lands. In a wet room the whole shower zone is graded to fall to its low point — the drain — so that the moment you turn the shower off, the floor begins clearing itself. It is the difference between a floor that dries on its own and one that holds shallow puddles until they slowly evaporate.
The reason it matters so much is that everything else in the floor depends on it. Standing water is the enemy of a wet room: it encourages limescale and grime, it makes the floor feel unpleasant underfoot, and over years it works harder on the grout and seals. A properly graded floor keeps the surface dry, keeps the room hygienic and lets the waterproofing beneath do its job cleanly, because water is always being guided somewhere rather than pooling in one spot.
Not too shallow, not too steep
Forming a fall is a balancing act. Too little slope and water sits in flat spots and puddles; too much and the floor feels noticeably tilted, tiles look wrong and it becomes less comfortable and less safe to stand on. The aim is a subtle, even gradient you barely register with your feet but that water finds instantly. As a rough guide, wet room falls are typically formed at around 1:40 to 1:80 — roughly 12mm to 25mm of drop over a metre — with the exact figure chosen to suit the drain type and tile size. A single point drain generally needs a slightly firmer fall from all sides; a linear channel can run a gentler fall in one direction.
The two ways to form a fall
There are two established ways to build the slope into a wet room floor, and the right one depends almost entirely on what your floor is made of. Solid concrete and suspended timber behave very differently, so we choose the method at survey once we know what we’re working with.
Pre-formed shower former
A rigid, factory-made board with the fall already engineered into it, cut into the floor and fixed down — the usual choice on a timber subfloor. Because the gradient is manufactured in, it is consistent and accurate every time, and formers are low-profile, which matters upstairs where head height and joist depth are tight. They come sized for point or linear drains, and the drain position is set by the product. For most upstairs conversions in Plymouth, a former is the sensible, predictable route.
Screed to falls
On a solid concrete floor we build up a sand-and-cement screed and hand-rule it to the correct gradient across the whole zone. It takes more skill and more time, but it gives complete freedom over the drain position and the shape of the room, and it’s the traditional, hard-wearing approach that has kept wet rooms draining for generations. Where a room is an awkward shape, or the drain needs to sit somewhere a former doesn’t offer, screed-to-falls is the answer.
Both methods end at the same place: a floor that slopes cleanly and evenly to the drain, ready to be waterproofed. The choice between them is practical, not a matter of quality — a well-laid screed and a well-fitted former both give an excellent fall. What decides it is the structure beneath, the head height available and where the drain needs to go, all of which we assess before quoting so you’re never sold the wrong method for your floor. Our upstairs timber floor guide goes deeper on the joist and head-height side of things.
Drain position and the low point
The fall and the drain are two halves of one decision — you cannot really plan one without the other, because the drain is the low point that the whole floor falls toward. Where the drain sits shapes how the floor slopes, which tiles suit it, and how the finished room looks.
Point drains
A single square or round gully, often set within the shower zone. The floor falls toward it from several directions at once, which means the tiling has to bend around a slope that runs more than one way. That naturally suits smaller-format tiles and mosaics, which flex around the fall with more grout lines for grip. It’s a cost-effective, reliable arrangement and a good match where the existing waste sits centrally.
Linear (channel) drains
A long, slim slot drain set against a wall or across the entry to the shower zone. Because the floor only has to fall in one direction toward the channel, you can use large-format tiles and get that clean, minimal, continuous look. The gentler single-direction fall is also easier to walk on. It costs a little more, and it’s our most-requested option for modern wet rooms. The full comparison lives on our linear versus point drainage guide.
Whichever drain you choose, it ties into your existing waste run. Where the original waste sits too high for a level-access floor, we re-route or drop it so the finished floor stays flush with the rest of the room — a detail that matters a great deal in older Plymouth properties around Peverell, Mannamead and Devonport, where waste positions weren’t planned with wet rooms in mind.
How wet room floor falls are formed, step by step
Here is how we build the fall into a floor on a typical Plymouth wet room. It happens early in the job, before any waterproofing or tiling, because everything above it has to follow the slope it sets.
1. Survey the floor and set the drain
We check whether the floor is solid or timber, confirm the head height and joist depth, and agree where the drain and low point will sit around how you’ll actually use the room. This decides which method the floor needs.
2. Prepare the structural floor
The subfloor is exposed, checked and made sound — any rot, movement or damp in a timber deck is put right, and a concrete slab is cleaned and prepared — so the fall is built on something solid.
3. Fit the former or lay the screed
On timber, the pre-formed former is cut in and fixed down. On concrete, the sand-and-cement screed is built up and hand-ruled toward the drain. Either way the fall now takes shape.
4. Set the drain at the low point
The drain body is set at the exact low point and levelled so its top finishes flush with the tiled floor to come. Its height is worked out from the tile and adhesive thickness, not guessed.
5. Check the fall with a level
We check the gradient across the whole zone with a level before anything goes over the top, confirming it runs cleanly to the drain with no flat spots or reverse falls. This is the moment to correct it, not later.
6. Waterproof over the fall
Only once the fall is right does the tanking membrane go over it, following the slope up to and bonded into the drain. The waterproofing is shaped by the fall beneath it, which is why the fall comes first.
The order is the whole point: form the fall, prove the fall, then waterproof it. Tanking a floor before the slope is right just locks in a puddle. If you want to see how the two connect, our tanking and waterproofing guide picks up exactly where this one leaves off.
Considerations before you commit
A few practical things shape what’s sensible for the fall in your particular room. We check all of them at survey, so you get a floor that suits the space rather than a compromise you only notice once you’re living with it.
Head height
A screed build-up raises the finished floor level, which eats into head height and can affect a door. A low-profile former is often the answer where every centimetre counts — one reason formers are so common upstairs and in loft conversions.
Joist depth upstairs
On a timber floor, the joists have to carry the former, the waterproofing, the tiles and the drain, and the drain needs somewhere to run between them. We check joist depth and direction so the floor is strong and the waste can fall away cleanly.
Tile size to suit the fall
Big tiles can’t bend around a slope that runs in several directions, so a multi-directional point-drain fall suits smaller tiles or mosaics, while a single-direction linear fall lets you use large-format tiles. The fall and the tile choice are decided together.
These trade-offs are why the floor is planned as one system — structure, fall, drain and tile together — rather than as separate decisions made on the day. It’s also where a fixed written quote earns its keep: the method and finish are agreed up front, so there are no surprises when the floor comes up. For how the falls sit within the wider job and budget, see the main wet room installation page and our Plymouth bathroom cost guide. If a level-access wet room isn’t the only option you’re weighing, our walk-in showers and tiling and flooring pages are worth a look too.
Floor formers & falls FAQs
What is a “fall” in a wet room floor?
A fall is a gentle, controlled slope built into the floor so water runs to the drain instead of sitting where it lands. The whole shower zone is graded to fall toward its low point — the drain — so the floor clears itself the moment the shower is turned off. It’s what makes a wet room self-draining rather than a floor that holds puddles.
How steep should a wet room floor be?
Wet room falls are typically formed at around 1:40 to 1:80, which is roughly 12mm to 25mm of drop over a metre, with the exact figure chosen to suit the drain and tile size. Too shallow and water puddles in flat spots; too steep and the floor feels tilted and less comfortable underfoot. The aim is a subtle, even gradient you barely notice but water finds instantly.
Should I use a pre-formed former or a screed to falls?
It depends on your floor. A pre-formed shower former suits timber subfloors — it’s low-profile with the fall engineered in, so it’s accurate and ideal where head height is tight. A screed to falls suits solid concrete floors and is hand-ruled to the gradient, giving total freedom over drain position and room shape. Both give an excellent fall; we choose the right one at survey based on your structure.
Where does the drain go?
The drain sits at the low point that the floor falls toward, and its position is planned around how you use the room and where the existing waste runs. A point drain often sits within the shower zone with the floor falling to it from several sides; a linear drain sits against a wall or across the entry with the floor falling in one direction. Where the existing waste is too high for level access, we re-route or drop it.
Why are the falls formed before the waterproofing?
Because the tanking membrane has to follow the slope. If the floor were waterproofed first and then sloped, or waterproofed while flat, the water would have nowhere consistent to run and could pool behind the membrane. Forming the fall first — and checking it with a level — means the waterproofing is shaped by the gradient and guides water straight to the drain.
Can I have a wet room floor upstairs on timber joists?
Yes, and it’s common. Upstairs wet rooms usually use a low-profile pre-formed former, which suits timber joists and limited head height and carries the fall accurately. The key is checking joist depth and direction so the floor can carry the build-up and the waste can run away cleanly between the joists. Our upstairs timber floor guide covers this in more detail.
Does the fall affect which tiles I can use?
Yes. A point drain creates a fall that runs in several directions at once, and large tiles can’t bend around that, so it suits smaller-format tiles or mosaics with more grout lines. A linear drain gives a single-direction fall that large-format tiles handle comfortably. We decide the fall and the tile choice together so the two work as one. A correctly formed fall is also subtle enough that you barely register it underfoot — the slope is only there to move water.
Where the fall fits in the whole floor
The fall is the foundation everything else in a wet room floor is built on — the waterproofing follows it, the drain sits at its low point and the tiles are cut to suit it. If you’re planning a project, it makes sense to read this alongside our guides on tanking and waterproofing and linear versus point drainage, and to start from the wet room installation hub for the full picture. A floor formed to a clean, gentle fall is one of those details you never think about again — which is exactly how it should be.
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Get your wet room floor formed properly
A wet room that drains cleanly starts with the fall. Tell us about your room and we’ll visit, check the floor structure, head height and waste run, and give you one clear written quote — expertly graded, fully tanked, finished properly. No surprises, no pressure.