Wetroom Materials Calculation Guide

When tanking your wetroom project it is of critical importance to order the correct quantities of CE approved waterproofing materials. If in any doubt you can phone us on 01387 270252 and take advantage of our free calculation service. Alternatively you can use the guide below to calculate your requirements:

Area to be tanked

The Entire floor area of the wetroom MUST be waterproofed.

The bottom area of the walls MUST be waterproofed all the way around the room, turning up from the floor by min.100mm

Any walls in the immediate shower area or “wet zone” should be tanked floor to ceiling; this area would normally extend at least 1.2m from the shower head. If using a shower screen the wall waterproofing can finish 100mm beyond the screen. On walls with no screen the waterproofing can be angled down towards the floor over a further meter, this area is the splash zone.

How do I calculate the surface area to be waterproofed


If you have a rectangular or square shaped room, just multiply the length in m. by the width in m.

If you have a less regular shape try and break it down in to rectangle or square sections then add the answers together. If there are any curved areas these can normally be squared up for calculation purposes.



Firstly work out the area of the 100mm “turn up” onto the walls. To do this simply add the length in m. of every wall in the room together and multiply the answer by 0.1.

Immediate Shower Area Walls

To calculate the remaining wall area to be coated measure the length of the walls likely to be subjected to driving water in the vicinity of the shower. This area would typically be 1.2 m from the shower head. This is called the wet zone, to work this out simply multiply the length of this area in m. by the height of the walls in m. If using a shower screen the waterproofing can terminate 0.1m beyond the screen.

Where no screen is used slope the waterproofing down to meet the 100mm turn up over an additional 1m. length. This is called the splash zone, for each angled splash zone multiply the wall height in m. by 0.5m.

Now add them together

We have now worked out the square meters required to waterproof the wetroom. Just add up all the totals as in the example below:

Total Floor Area = 3.0 sq.m.

Turn Up = 0.74 sq.m.

Wet Zone = 5.06 sq.m.

Splash Zone = 1.1 sq.m.

Total Waterproofing 9.9 sq.m.

How much joint tape do I need?

You require enough joint tape to re-enforce the entire wall to floor junction around the perimeter of the room. In the example above this is 1.5+2+1.5+2 = 7 lin.m . You also need to seal all other joints and junctions, in the above example this relates to the two sides of the shower tray former that are facing out into the room as well as the joint in the flooring boards at point a). This works out at 0.8m+0.8m+1.2m = 2.8 lin.m. Any wall to wall joints in the wet zone or splash zone of the walls also need jointing tape. So at point (b) we also need a strip of tape running from floor to ceiling = 2.2m. Therefore the total amount of jointing tape required is 7+ 2.8 + 2.2 m = 12 lin.m.

What about Sleeves and Corners?

Large sleeves or “outlet sleeves” are normally used for connecting the waterproofing material into your chosen waste outlet, you normally need one per wetroom. The exception to this is if a toilet waste pipe penetrates the floor or if you have any other large penetrations in the floor or in the wet zone and splash zone areas of the walls. If this is the case you would need one additional large sleeve for each penetration.

Small Sleeves or “Pipe Sleeves” are normally used for sealing the hot and cold shower supply pipes where they penetrate the wall into the back of the shower mixer. Additional Small Sleeves will be required if there are any other small diameter pipes penetrating the floor e.g. radiator pipes or sink / toilet inlet pipes.

Pre-Made Internal or External Corners are very useful for detailing the jointing tape through 90 degree corners. To calculate the number of corners required simply count up the number of internal and external 90 degree corners you have in your room. The examples below show some typical configurations and the number of corners required for each.



We hope the above guide is useful in helping to calculate the exact waterproofing requirement for your wetroom. If in any doubt just give us a call and we will be happy to work out exactly what you need.

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Take a look at our other useful wetroom articles: all written to help you create the perfect wet room regardless of size or location.