Wet Room Drainage & Floor Falls Guide

Wet Room Drainage and Floor Falls: Getting the Detail Right

The drain and the fall of the floor towards it are what actually make a wet room work day to day. Get the fall too shallow and water pools, get it too steep and it looks and feels wrong underfoot. This guide covers drain types, correct fall ratios, and the practical constraints that decide which option suits your floor.

Key takeaways

Correct falls sit between roughly 1:50 and 1:80, both too shallow and too steep cause problems.

Trap depth, not preference, often decides whether gravity drainage is possible.

Pumped drainage is a genuine option where gravity fall isn't achievable.

Drain position relative to existing waste runs affects both cost and disruption.

Linear drains vs point drains

A point drain sits centrally, or in a corner, of the shower area, with the floor falling towards it from all directions, similar in principle to a traditional shower tray but built into the floor itself. A linear drain is a channel, usually along one wall or at the threshold of the shower area, with the floor falling in one direction only towards the channel.

Linear drains tend to look neater and allow larger tile formats to be used with fewer cuts, since the fall only runs one way, but they need a slightly longer, more consistent slope. Point drains are often simpler to install on smaller floor areas or where joist direction restricts options, but usually mean smaller tiles or more cutting to accommodate the fall from multiple directions.

Correct fall ratios and why they matter

Wet room floors are typically built with a fall of between 1:50 and 1:80 towards the drain, meaning the floor drops between roughly 12mm and 20mm per metre of run. Too shallow, below around 1:80, and water can sit rather than run away, particularly noticeable with lower flow showers or if the floor settles slightly over time.

Too steep, tighter than 1:50, and the floor starts to feel uncomfortably sloped underfoot and can make larger tiles harder to lay neatly. Getting this right depends on the size of the room, the drain position and the floor build-up available, which is why it needs calculating properly rather than guessed on site.

Trap depth and how it affects your floor build-up

Every drain needs a trap to hold a water seal and stop smells coming back up from the waste system, and the depth required for this trap is often the single biggest constraint on whether a wet room can be built into an existing floor without raising it. Shallow-depth traps exist specifically for retrofit wet rooms where ceiling height below is limited, but they still need a minimum depth, commonly around 45-65mm depending on the product.

On a concrete floor with no cavity beneath, achieving this depth without raising the floor level significantly can be difficult, which is one of several reasons a site survey is essential before quoting a project rather than pricing from photos alone.

Pumped drainage as an option

Where gravity drainage isn't achievable, usually because there isn't enough depth available to fall to an existing waste run, a macerator or shower pump can lift the waste water up and away to the nearest drainage point. This is more common in basement conversions or ground-floor wet rooms a good distance from the existing soil stack, less commonly needed in a straightforward en-suite conversion.

Pumped systems add an extra mechanical component that needs occasional servicing, and most have an audible sound when running, worth being aware of if the wet room is near a bedroom. They're a genuinely useful solution when gravity drainage isn't physically possible, but they're not the first choice where a gravity-fed drain will work.

Drain positioning relative to existing waste runs

Positioning the drain close to the existing bathroom waste pipe run keeps costs down and avoids extensive floor or ceiling disturbance to route new pipework. This is a major factor in whether a linear drain along a particular wall, or a point drain in a specific corner, makes sense for your layout, rather than purely aesthetic preference.

On upper floors, the waste pipe run below also needs enough fall of its own to carry water away efficiently, which can be a real constraint in older properties with shallow floor voids, again something a proper survey identifies before any quote is finalised.

Getting the design right from the outset

Because drain type, fall direction, tile size and trap depth are all interlinked, changing one after the floor has been opened up usually means starting the floor preparation again. This is why we walk through drain options during the free design and quote home visit, using the actual floor structure and existing plumbing runs rather than a generic layout.

A written specification setting out drain type, fall ratio and tile size before work starts avoids surprises partway through the job, and it's worth asking for this in writing from any fitter, not just a verbal description.

Quick questions

Which is better, a linear drain or a point drain?

Neither is universally better, it depends on your floor structure, room shape and tile choice. Linear drains suit larger format tiles and a cleaner look, point drains are often simpler where floor depth or joist direction is restrictive.

How do I stop a wet room floor feeling too sloped?

A correctly calculated fall, generally between 1:50 and 1:80, should feel barely noticeable underfoot in normal use. If a floor feels distinctly sloped, the fall may have been set steeper than necessary, often to compensate for insufficient floor depth elsewhere.

Can I add a wet room drain to an upstairs bathroom?

Usually yes, but trap depth and the fall available in the waste pipe run below become the key constraints, which is why an upstairs wet room conversion needs a careful survey of the floor void before it's quoted.

Do wet room drains get blocked more easily than a shower tray waste?

Not inherently, though linear drains with a removable cover are generally easier to keep clear of hair and debris than a small point drain grate, worth factoring into your choice if easy cleaning matters to you.

What happens if the fall is built wrong?

Water will pool rather than drain fully, which shows up as standing water after showering and can eventually lead to slower drying, staining or grout breakdown. It's a floor-structure issue, not something that can be fixed by re-grouting, so it needs identifying at installation stage.