Can I Have A Flush To Floor Shower Tray?

Wet rooms have a tiled or vinyl floor and there is no step up into the shower area.

Low profile shower trays can be fit flush to the floor as above…..

or on a riser kit as above, which lifts the tray approximately 10cm off the floor.

For the purposes of this article I will be discussing flush or raised shower trays, rather than wet room trays.

Please see here for more information on that particular subject.

Before saying whether or not you can have a flush shower tray, a bit of background understanding is required:

This is what the installation of a flush shower tray looks like:

Waste pipework is installed under the floor (to carry away the waste water from the shower to the soil pipe normally located on the outside of your house).

The floor is replaced with a hole cut for the trap (which is attached to the pipe).

The tray is then dropped into position, levelled and effectively glued into place and the trap is connected to the tray (the trap is already attached to the pipe as you have seen).

However, it is not always possible to install a flush shower tray, and this is something that a remote bathroom planner (in Bathstore etc) will not be able to tell you as they haven’t set foot in your bathroom……

This is also one of the perils from ordering online without the advice of an experienced bathroom installer.

Such as….

Waste pipework cannot be easily fitted under the tray as required unless it is chased out as shown above – this is not always possible, practical or cost effective.

Sometimes the void under the floorboards beneath the shower tray is too full of pipework to run a waste pipe or to fit a shower trap.

Often this will not become known until after work has begun (as you will not know exactly what is under the floorboards until they are removed.)

In some instances the trap may fall onto a critical joist and therefore fitting it in this location would require excessive notching of the floor joist in order to physically fit the trap into position under the floorboards.

This is never fully recommended as it can weaken the floor structure, unless further precautionary measures are taken.

PS Picture above are courtesy of an excellent Essex based builders website which highlights what you can do in this situation (notch as necessary & then re-strengthen the joist essentially).

Above is another example where the joists had been previously heavily notched so when we put in a new shower trap we reinforced them where necessary (you can see how we have started to piggyback one joist that the pipe runs through with another piece of timber to strengthen it.)

In the example above, the tray needs to be raised to drain downhill into the WC waste pipe (which as you can see is situated above floor level.

The distance that the waste water has to travel may also mean that the tray has to be raised in order to maintain an adequate fall to the point where it exits the building and is connected to the soil pipe outside (usually).

The minimum fall on waste pipes varies with the overall run length from approximately 2cm/m to 10cm/m.

Joist direction can also affect whether you choose to run the shower waste over the floor (with the tray raised up on a riser kit) or under it.

It is difficult to run large bore (40mm+) shower waste pipes through joists as above.

This approach weakens the joists, which can lead to tiled floor installations cracking (as the floor flexes) and other structural problems.

It also takes longer to do and is more expensive, though steps can be taken sometimes to mitigate the risk (by reinforcing the floor in other ways when possible.)

The structural integrity of the existing joists is also a factor that you may wish to consider when assessing whether you want to thread a waste pipe through the joists.

Old houses with old joists that may have been weakened by excessive notching in the past, woodworm, leaks leading to rotting etc will not react well to having (more) large holes drilled in them!

It is much easier to run waste pipes in between joists as above.

PS Large runs of pipe should be supported to prevent the pipe from sagging over time.

PS If your bathroom is on the ground floor you may be able to run the waste under the floor joists as here:

The limiting factor here is normally the ground level outside, as the pipe needs to exit the wall above the ground to connect to the soil pipe or drain into a gulley normally.

Raised shower trays are exactly the same as flush shower trays but they have an additional ‘riser kit’ which serves to lift them off the ground by approximately 10cm. This gap is then normally filled with a custom plinth.

This allows the trap & waste pipework to run above the floorboards.

Riser kits (sometimes called leg set & panel kits) typically consist of adjustable legs and a plinth, and they are specific to the tray manufacturer.

A plastic plinth normally fills the gap between the underside of the tray and the floor but there are alternatives…..

Such as a tiled shower tray riser – this should be made to be removable ideally, so should be fitted after the floor has been tiled.

1. 1. It can be run under the floor if possible as with flush mounted trays.
   2. Or it can exit the building under the shower tray itself (normal scenario)
   3. Alternatively, pipework above floor level (from a raised shower tray) can be run in behind a wall….

4. Or against the walls, which can be then be boxed in…..

Hopefully you should now have an understanding as to why its not a straight forward yes or no answer to the question of whether you can have a low level shower tray!

If you want a recommendation of shower trays please email me at chris@ukbathroomguru.com

Chris