How to Create a Successful Wetroom Design

Wetroom design – Angle of the Wet-Room Floor (Slope to Falls)

A good wetroom design is equally important for small or large spaces and often provides a simpler and more practical solution than trying to accommodate a conventional shower or bathroom in a small area. There are four main Wetroom design criteria that must be considered before embarking on any wet-room project:

Wetroom Design

Wetroom design – Angle of the Wet-Room Floor (Slope to Falls)

The Slope to Falls is the required incline in the floor that runs from the edges of the designated wet area to the waste outlet. The minimum recommended fall is 15mm and the maximum recommended ratio is 85:1, (i.e. for every 85mm the incline travels towards the waste outlet the floor level will fall 1mm.)

It is imperative that the slope to falls is formed into the floor itself. The floor must not be flat and you should never try to create the falls with tiling.

The easiest way to create this “slope to falls” is to use a “Shower Tray Former”. These can either be bought in stock sizes with set waste positions or alternatively bespoke formers can be made to your exact specifications.

The Shower Tray Former can be installed onto a wooden deck or a concrete floor.

Wetroom Floor – Structural Rigidity

It is important that a wetroom floor is rigid and stable prior to tanking & tiling. Obviously, on a concrete floor this is not an issue, but on a wooden deck the joists will need to be stabilised in the immediate shower area and this is done by constructing a sub floor within the joist space using 18mm Plywood. The minimum recommended thickness of the flooring to be laid on top of the joists is 20mm as recommended in Building Regulations.

Ideally a Shower Tray Formers would be installed directly over the sub floor and then the rest of the floor would be over laid with 24mm marine grade plywood or a quality WBP board. We would not recommend using chipboard.

Wetroom Drainage (Waste Outlets)

The wetroom drain (waste outlet) should be a top accessed, trapped unit with a constant flow rate in excess of the output of the shower running at full capacity. The waste outlets can be supplied as standard with Shower Tray Formers and in this case should have a constant flow rate of 46 litres per minute, which is normally more than adequate for a regular wet-room shower arrangement.

However, if the wet-room is to have body jets and a deluge shower head etc, then an upgraded waste may be required. In this case waste units with constant flow rates of 60 or 120 litres per minute can be purchased as separate units.

Wetroom Waterproofing (Tanking)

All wet-rooms must be tanked. Unless the designated shower area is to be completely isolated within the bathroom by partitions, then the minimum requirement for waterproofing a wet-room is to do the entire floor area, turn up the walls a minimum 100mm and floor to ceiling to the walls in the immediate shower area. If the area is isolated then the waterproofing can be restricted to that area, but should extend beyond it by a minimum 300mm.

The waterproofing system must follow the contours of the slope to falls (hence the reason why the incline must be formed into the floor) and be dressed into the waste unit to seal it.

Our Aquaproof Wet-Room Tanking System is applied to the floor and walls and can be tiled over in the normal way using a proprietary flexible waterproofed tile adhesive and grout. The Aquaproof system can be applied to any traditional building material, but some substrates such as brickwork will require a certain amount of preparation prior to application and this is outlined in our Application Guidelines.


Wetrooms are a stylish and practical addition any home no matter the size of space you have available and provided you follow the guidelines outlined above there should be no reason why they should ever cause any problems.

Contact us to find a reputable wetroom installer.