Wetroom Floors & Drainage Guide

Once you have your ideal wetroom in mind and have a floor layout formulated it is time to start working out the details. The next important factor is the floor and drainage, while this can be a complicated part of the process, this guide is here to make things easier. 

Wetroom Floor Design
Whilst there are many ways of installing a practical wetroom floor, all techniques involve creating a slope in the floor towards a drain, in this wet area the floors and walls are tanked to ensure no water can make its way to the building structure. 

Wetroom Floor Basic Structure

The easiest and most reliable way to do this is to use one of our Wetroom Kits, these kits include a wetroom tray, drain, grid and tanking system and will be the focus of this guide.

A guide to choosing the right wetroom kit can be found here. 

Shower Water Splash Zone

Size of the Wet Area
Try to go with the largest wetroom tray you can reasonably fit in the shower area, this will catch as much over spray as possible.
You should also keep in mind that the 
shower pressure, shower head size and mounting position of the shower head will influence where water will go, with so many variables we are using a typical rainfall shower head as the basis for this guide. 
The stream of water flowing from the shower head and off the body is approximately 1000mm in diameter at floor level. 
The splash area is approximately 2000mm at floor level.
Shower screens will help contain this water. 

The Existing Floor Structure.
The type of floor structure may influence which type of wetroom tray you wish to use. Whilst both the Maxxus and Underlay styles of wetroom tray can be used on almost all floor types, the installation method of each tray is different. 
You can compare the Maxxus and Underlay trays here.

As a tiled level access wetroom is most common we will briefly cover these differences below.
For detailed installations instructions for all our wetroom systems please go here. 

On Timber Floors first the floor boards are removed where the tray is going to be installed.

Maxxus trays are the easiest and fastest to install, they are a structural tray, so this means they can normally be screwed straight down to joists without any extra support. 

Maxxus Wetroom Tray Installation on Timber Floor

Underlay trays must be fully under boarded, this is normally done by fitting 18mm ply level with the top of the joists. 

Underlay Wetroom Tray Installation Timber Floor
Wetroom Tray Installation on Concrete Floor

On Concrete Floors the area where the tray is to be installed is typically chipped up to enable the tray to be set flush with the existing floor, both the Maxxus and Underlay trays can be sat on a cement mix or tile adhesive. Maxxus trays must also be screwed down, Underlay trays must be fully supported with no cavities underneath. 

Wetroom Drainage

All our drains and traps comply with British Standards and Building Regulations, installers must ensure that the drainage system also complies with these regulations. These are stipulated in “Building Regulations part H” in particular Part “H1”, it states "the requirements of H1 will be met if a foul water drainage system;
a. conveys the flow of foul water to a foul water outflow (a foul or combined sewer, a cesspool, septic tank or holding tank);
b. minimises the risk of blockage or leakage;
c. prevents foul air from the drainage system from entering the building under working conditions;
d. is ventilated;
e. is accessible for clearing blockages; and
f. does not increase the vulnerability of the building to flooding."

The full regulations can be downloaded form the government planning portal.

Drainage Waste Pipe Runs
Please note: this is a guide only, check the regs for full details and alternatives.
The waste pipe from wetroom drains is almost always 40mm plastic pipe (solvent weld, not pushfit).
This should be routed in such a way that it has;
a.  the minimum amount of joints and angles; 
b. a gradient between 18mm and 44mm per meter; and
ca maximum horizontal run of 3 meters (increased to 4 meters if 50mm pipe is used, and 10 meters if an air admittance valve is used).

Wetroom Drainage Pipe Gradient Guide
Wetroom Drainage Maximum Waste Pipe Run Length Guide

d. support over long runs to prevent sagging and maintain the gradient;
e. a means of clearing any blockages in the pipe. For this reason keep any inaccessible pipe work as straight as possible (use “swept” bends if necessary) with as few joints as you can and provide an accessible rodding point (or a joint outside that you can dismantle).   You can also use a “Flexible Rod Drain Un-blocker” through the body of the wetroom drain so it should be fairly easy to comply with this requirement.

Wetroom Drainage Swept Bend Example
Timbre Joist Hole Drilling Guide

Waste Pipes That Pass Through Joists
Before deciding to run a waste pipe through floor joists consider of there are any alternative ways to run the pipe i.e. through an external wall and round the outside of the building or into the room below. Do not notch the top of the joists.
Running the waste pipe through floor joists is not ideal however it can be done and on some installations is simply unavoidable.

Before commencing, consult the Building Regulations for more detailed information on the notching and drilling of floor joists.
It's important to understand where you can and cannot drill a floor joist, the maximum diameter of the hole and how close this can be to existing holes or notches. 
Key points to remember;
a. holes can only be drilled in the centre of the joist;
b. holes can only be drilled between 0.25 x S and 0.4 x S from the wall (S = span of the joist in mm);
c. holes can be no larger than 0.25 x D (D = depth of the joist in mm);
d. holes must be kept at least 3 times the hole diameter apart.
e. holes must be kept at least 100mm apart horizontally from notches. 

For example - a floor joist spanning the room is 2400mm long and 180mm deep.
You can drill a maximum hole size of 45mm diameter (0.25 x 180 = 45). 
The hole can only be drilled between 600mm (0.25 x 2400 = 600) and 960mm (0.4 x 2400 = 960mm) from either wall.
The hole must be drilled in the centre of the joist.

As you can see, depending on the joist depth, it may be difficult to route the waste through joists whilst maintaining the gradient needed. If the joists must be drilled outside of these parameters the floor may be weakened, consult your building control office, there are methods for strengthening the joists.