Understanding wet room shower drainage

 Different wet room floor constructions require different solutions

A Wet room floor drainage gully

It might sound obvious, but a wet room shower floor needs a means for the water to drain away. This simple yet important fact is the starting point for planning your wet room - the drainage gully.

It is surprising how many people overlook this fairly obvious 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 pipe work! Check your levels.

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.

There is plenty going on below floor level so you need to consider what type of floor you have and what you will need to install to make things work. For example, is it a suspended timber floor or is it solid with say a screed finish?

No matter what type of floor you have there is usually a solution, but think about it at the conceptual stage and you won't end up with awkward problems to overcome.

The floor construction determines which type of drainage gully will be best for the job.

Creating a wet room shower floor - The Fall

Although your objective (to create a fall towards the drain) will always be the same no matter what type of floor you have, the components you will use can differ quite a lot.

Installing to a timber floor...

You can 'have a go' at creating the slope yourself. After all, what could be that difficult? Well, you might be surprised. To create a strong, durable, constant yet subtle slope from the perimeter of your shower area to the drainage gully can be a feat of engineering. Your slope must arrive at a gully at the correct level which must be fixed securely at a convenient location. All of this must sit on the joists supporting the surrounding floor and must never move or flex. OR...

You might be better off using what is known as a preformed 'Floor Former'.

These are available in a comprehensive range of sizes and shapes. Depending on how large a shower area you want formers can be one-piece or in multiple segments. They take the guesswork out of this complicated task ensuring you get the perfect slope and an outlet into which you secure your waste gully. Installation is simple. When installing to an existing timber floor you lay the former where you wish to position your shower area. Mark around the former then remove it. Cut out the area you have marked - exposing the joists. Insert your floor former in place of the removed floor boards. Depending on the product some will sit directly on the exposed joists, others require you to under-board between the joists thereby creating a flat level surface on which to sit the former. Once fixed down the former (which is manufactured to be the thickness of a standard floor board) simply takes the place of the floor you have removed, but now it has a perfect pre-formed slope towards the gully outlet.

Wet Room shower floor formers

Installing to a solid floor...

In most cases you can still use a floor former fitted into a rebate in the floor that you excavate, bedding it in so the top edge of the former aligns with the surface of the surrounding floor. OR...

You can use a drainage gully specifically designed for you to screed up to. You simply establish an area in which you will create your shower area, install your drainage gully setting it to a slightly lower height, then screed between using a plaster's trowel. When the screed hardens you have a sloping area ready for the tanking membrane to be applied with the gully drain wherever you have decided to set it. Once again, a simple installation.

In all installations you will need to make provision for the waste pipe from the drainage gully. With a timer floor this might be between, under or through floor joists. With a solid floor this is likely to require excavation of a channel in which to run the drainage pipe. Always make sure the waste pipe maintains a positive fall along its length.

Drainage Gullies for solid floors

Wet room floor coverings and gully types

In the main, there are two popular types of floor covering - a tiled finish or a non-slip vinyl. Which one you choose will have an effect on the gully type you must use. For example, if you are planning to tile the floor you would use a square or linear shaped drainage gully. If you intend to use vinyl it is best to use a round gully. The reasons are fairly simple.

1. Square and Linear drainage gullies. It is easier to cut a tile in straight lines, hence square and linear shaped gullies lend themselves with their straight edges. The tiles are cut to butt up to the gully frame and the edges finished with silicone and/or grout.

2. Round drainage gullies. With vinyl, to ensure perfect water tightness the floor terminates at a round gully under a circular compression flange that squeezes down on the edge of the vinyl to create a neat water seal.

   It is very difficult to create the same watertight integrity for vinyl using a square or linear gully as there is no means to clamp the edge in the same watertight manner. The vinyl would need to be adhered to the flange surrounding the gully which over time may not remain watertight.

Waterproof tanking membrane for a wet room floor

When tiling a wet room floor it is essential to use a waterproof tanking membrane before you tile. We supply TILESURE. The membrane adheres to the timber floor or substrate. When installed you can then spread your tile adhesive directly on the surface of the membrane and begin the process of tiling.

If you are using a vinyl to cover the floor and shower area this will act like a waterproof membrane so there's no need for an additional membrane.

Take Care when using under-tile heating

If you intend to use Under-tile Heating (a thin electrical heating element) you would apply that after you install the tanking membrane before applying your tile adhesive (i.e. within the adhesive layer). Great care should be taken that the trowel does not nick or damage the heating element when applying, spreading and combing the adhesive. A metal trowel has sharp edges that become sharper with use, eventually presenting like blades. It is so easy to cause damage to the heating element without realising. This will result in premature failure of the heating system. In such an event you will have no choice than to rip it all up and start again!

For this reason, whenever you are applying tile adhesive over an electrical heating element you should consider using a plastic trowel. Care should still be taken, but a plastic trowel is unlikely to develop razor sharp edges.

You should check the Wattage (W) of the heating element before installation. A waterproof tanking membrane will only tolerate so much heat before you melt a hole in it!

The tanking membrane we supply is called TILESURE. This is capable of handling 150W per square metre. This is a market leading product.

If you have the luxury of a wet underfloor heating system (a system of pipes carrying hot water from your household central heating boiler) it is installed in a very different way (usually installed within the slab of a solid floor or between the joists of a timber floor), will not reach such high localised temperatures and will never come in direct contact with the tanking membrane. Hence, you need not worry about damaging the membrane.

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.

Shape of a wet room shower gully

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

A linear gully A long narrow gully. Shown here with a single outlet trap spigot. (the model shown is for use in a screed floor but without brackets will be used with linear floor former).	A square gully Assembly showing a typical square gully for use with a floor former on a timber floor. Picture shows a water trap with horizontal outlet spigot.
Screed floor square gully outlet For a tiled floor surface for a screed floor. There are variants of this gully including a 'tile inside' gully cover.	A round gully Round gullies tend to be used with vinyl floor coverings such as Altro waterproof non-slip. The edge of the vinyl clamps under ring to form a neat watertight edge.

What type of wet room floor gully to choose

The type of gully you choose for your wet room floor is more often than not purely aesthetic. However, drainage gullies with straight edges lend themselves to a tile finish more so than a round gully, simply because straight cuts are easier with tiles than curves. Conversely, a gully with straight edges does not have the means to clamp the edge of a vinyl floor covering so a round gully is preferred for this type of surface.

Before choosing between a square or linear gully consider how each will impact on the task of tiling.

Linear gullies lend themselves better to the use of large tiles.

Whether a linear gully is situated tight to a wall or away from the wall you will find large tiles generally require fewer cuts.  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.

Take a look at screed floor drainage gullies

a range of square and linear gullies for a screed floor with a tiled surface.

Take a look at timber floor wet Room shower floor formers

A range of floor formers formers with linear and square gullies for a tiled floor and round gullies for vinyl.

Pumped waste for a wet room shower floor

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

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 the simple principles.