Wet room shower drainage

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 Understanding wet room drainage - Getting waste water away from your wet room shower floor

Index > All about wet rooms > Wet room shower drainage

Wet room floor gully

It might sound obvious, but a wet room shower floor needs somewhere to drain to. This simple fact is the starting point for planning your wet room. It is surprising how many people overlook this fairly basic requirement, focussing more on appearance than functionality.

Establish where you intend to dispose of your waste water and how you intend to get it there. No good realising that water won't run up hill half way through the job, or that you haven't got enough depth to accommodate a water trap or pipework!

No matter what your installation may demand there is probably a solution, but think about it at the conceptual stage and you won't end up with nasty surprises or problems.

You should also consider what type of shower equipment you plan to install. No good putting in a system that throws a monsoon of water at you if the drain can only handle a meagre flow rate.

A wet room shower in a perfect world

Although a wet room shower may be considered attractive for its level access or understated simplicity, there is plenty going on below floor level. Whatever your drainage solution, that's where waste water will be channelled away for disposal. In a perfect world this is simply a matter of running a waste pipe from the water trap in the floor to a convenient drain. But things aren't always so simple. If the level of the drain into which you plan to run is higher than the wet room floor a pumped solution may be necessary. Even if a fall to the drain is available you still need to run the waste pipe. This might mean dodging or going through joists of a timber floor, digging or making provision for a channel through a solid floor. Consider how much depth you have below floor level to achieve this.

Consider how much water your drainage will be expected to handle. Exceed its capabilities and you may end up with water cascading down adjacent corridors looking for alternative ways out!

Ensure that slopes run towards the shower area and gully. Water finding its way outside the designated shower area will also look for a place to go. Ideally this will be back towards the shower gully, not in the opposite direction towards a corner of the bathroom, or worse still the hallway!

A simple bit of forethought and you'll create a prefect result.

Ways to drain a wet room shower floor

There are a couple of basic ways to drain water from a wet room. Either by gravity (allowing the waste water to run down a pipe with a constant fall towards a drain or with a shower waste water pump (lifting and pushing the waste water to a higher level).

You must decide which method of disposal you will use as the trap in the floor is subtly different for each.

Shown right: A normal wet floor waste will have a 50mm water trap (to meet with Building Regs) and an outlet spigot of 40 or 50mm onto which your waste pipe will attach. A constant fall must then be achieved on the pipework that will run to a convenient soil pipe or sewer as a 'gravity' flow.

Square wet room gully with horizontal outlet trap

Square wet room floor gulley with pumped waste outlet

Pictured left: A 'pumped waste trap' is not actually a trap at all. It is usually a very shallow device that rather resembles a small frying pan.

With this, the 'handle' of the pan is in fact a small bore spigot onto which small bore pipework can easily attach. This is then connected to a remote 'self-priming' pump.

While there are one or two exceptions to the above examples (for example, when using something like a Sanishower pump or a Grundfos Sololift) that will work with the larger bore outlet spigots you cannot swap between the two easily. Another reason to plan carefully.
Shown right: Another variation is the 'waterless trap'.

A slightly contradictory title as this device does not have a water trap inside. Instead, it has a membrane that snaps open in the presence of water and then closes when dry.

The advantage of these would be the very low profile extending below the floor surface, but be careful where you choose to use one.

Because they do not offer a 50mm water separation (to catch foul odours coming back from a sewer) they do not meet Building Regs if connecting directly into a soil pipe or sewer.

Square wet room floor gully with waterless trap

A waterless trap may be used if say you are wasting into a gully outside the building - but not connected directly into a sewer.

Whichever describes your scenario, remember to match the flow rate of the shower equipment to the flow handling capabilities of the wet room floor and gully setup.


Shape of a wet room shower gully

In general, there are two shapes of tiled floor gully - Linear (a long thin slot) or Square.

Linear wet room floor gully for a screed floor Square wet room floor gully

Above: A linear gully showing a single outlet spigot. (the model shown is for use in a screed floor. The galvanised angle brackets allow for fixing/levelling and hold the unit securely during installation)

Above: This is a typical square gully assembly showing the various components. On this model the wite trap has a horizontal outlet spigot onto which pipework would connect.


Round wet room floor gulley for vinyl floor coverings

Shown left is a round gully. These tend to be exclusively used with vinyl floor coverings such as Altro waterproof non-slip.

The variant shown has a 40mm outlet spigot, but they are available for pump connection (the frying pan) or with a waterless trap.

Drainage gullies with flat edges lend themselves to a tile finish more so than a round gully, simply because it's easier to cut a tile straight than it is on a curve.

While on the subject of tiling, you should consider which of the gullies (square or linear) will best suit your chosen tiles.

A square gully will invariably have four slopes converging on it.

If you are using large tiles this will require a degree of skill when cutting all the angles.

For this reason, it is often considered that small tiles are better suited to a square gully as they are easier to form being more forgiving.

Pictured right is a square gully shown with the optional 'tiled' cover. You can see the angular cuts required to tile.

The picture also shows how much less obtrusive the gully is with a matching tiled cover

Square wet room floor gulley showing angled cuts in large ceramic tiles and a tile-in gully cover

 Linear gullies tend to have a slope to the front and another to the rear (there are exceptions - especially on very large shower areas that employ a linear drain). This can often simplify the cutting of large tiles as there are no difficult angles to cut. (exceptions being larger areas with linear drains that may still require angular tile cuts at the corners)

Don't be fooled into thinking that a linear drain can handle a higher flow rate per se . Flow rate is highly dependent on a number of factors - capability of gully, size of waste pipe, fall on waste pipe to drain, etc. A linear drain with the same outlet size as a square drain will only handle the same flow rate. A bigger catchment area does not necessarily equate to a better flow. It is however fair to say that some Linear drains can be equipped with additional outlets (the Novellini Linear drain for example) that can increase the flow handling potential considerably.

Pumped waste for a wet room shower floor

When a wet room floor is lower than the drain into which it will dispose of its waste it is likely that a waste pump will be necessary.

Depending on available space and the distances (vertical and horizontal) involved, various pumps may prove suitable. It must be said, if there is any way to avoid using a waste pump then consider it well before electing to use one. Why add a mechanical device and a significant cost to something physics is only too happy to do for nothing?

Pictured right: A Dry Dec 20 shower waste pump installed within a wall behind an access panel.

The picture shows the pump, its control box (the brain), the two flow sensors located in the hot and cold supply pipes to the mixer shower equipment and a small canister that absorbs any shock waves created when the pump is scavenging for water.

This is a top end setup capable of handling high flow rates.

Smaller lower rated pumps are available with examples below:

Dry Dec 20 wet room floor waste water pump kit

Visit our section on Shower Waste Pumps

Waste water pump for wet room floor


Grundfos Sololift shower waste pump

Remember, evaluate what flow the pump must handle before buying or installing. If your pump can't keep up with the flow rate of your shower you will end up with a flood.

Shower waste pumps are normally activated on a signal from flow sensors placed in the supply pipes to the shower equipment. Mixer showers have two sensors (one in the hot supply, one in the cold supply). Electric showers, having only a cold water supply only have one sensor.

The more sophisticated the pump and the higher the flow handling capability the more expensive the unit will be. For more detail please don't hesitate to call.

To Conclude

In short, be mindful of a few simple things when planning and installing and all will be well. Remember what goes in (or on) must go out (down the drain). Gravity plays a major part so ensure slopes run the correct way. It really isn't rocket science but you will get caught out if you choose to ignore these simple principles.