Bathroom Design – Working With Soil Pipes

Working with soil pipes in small bathrooms is one of the trickier aspects of bathroom design.

The soil pipe is the large pipe that ducts toilet water out of the bathroom. These are very large and their position will be determined by your outside drainage. They are usually made from plastic but can be made of cast iron in older properties.

Sometimes these pipes run vertically down through the house internally. They can sometimes be run down the outside of the building (as is the case in our diagram). Moving them is not an easy job in most circumstances. They are usually the main factor that limits your ability to move things around to exactly where you want them.

So what are the options if it is limiting your desire to remodel your bathroom the way that you want to?


A Typical Small Bathroom Layout

In the diagram you see a typical small bathroom layout. The bath runs along one wall. The soil pipe is shown in red. It prevents the bath being fitted flush against the wall that the toilet is fitted to.

The worst option in this situation is also the one that most people adopt. They build a flat shelf at the end of the bath to fill the gap. And then tile it.

This solution is just one big problem waiting to happen. This is especially problematic if there is a shower over the bath.

Grout, and tiles themselves, are very brittle. They will crack if there is too much movement. The bath is not attached to a solid wall where it meets the tiles. There will just be a wooden framework at this position. This frame is liable to move slightly in use. The movement, however slight, leads to cracks in the grout. Cracks will lead to leaks.

Siting the shower at the other end of the bath will help. It will keep the majority of the shower spray away from the horizontal tiled area. But it is still problematic. Water will settle on the tile surface. The grout will absorb the moisture and mould will start to grow.

So what other options are there?

bathroom design soil pipe

Moving The Wall

This is not quite as dramatic as it sounds.

You can make a small stud wall at the end of the bath. This can be made from timber and then covered with a sheet material.

Use plasterboard or tile-backer boards if you are tiling the wall. Do not use plywood. It expands and contracts at a different rate to the tiles. The adhesive will loosen over time and the tiles will work loose.

Better still use bathroom wall panels instead of tiles. These can be fitted over any sub-surface and are totally waterproof. Wall panels can be fitted to plywood with no problems.

The difference with this solution is that it runs floor to ceiling. The framework can be anchored at the top and bottom making it much stronger. It will be much less prone to movement Any tiling will be vertical, so water will run straight off.

This solution also gives you the option to bury pipework for the shower making the whole job look neater.

You have other options if the shower is at the other end of the bath. This is the case in the photo shown.

The bathroom has had niches built into the wall. These look really attractive. They also offer practical storage which is usually in short supply around a shower area. If you fit lighting into the niches they look even better.

You will require shower-rated lights if you go down this route. There are different regulations for different areas of the bathroom when it comes to lighting. Inside the shower area are the most stringent.

bathroom design stud wall

Hiding Soil Pipes

If you are not able to change the location of you soil pip what are you other options?

One option is to extend it so the that toilet position can be moved along it’s existing wall.

You need to ensure that the pipe still has enough fall. This ensures that the waste water drain away quickly and effectively. You will also need to cover the extended pipework or it will look unsightly. There are two ways to achieve this:

  1. Box-in the pipe. The box work can then be tiled to help blend it into the design of the room. If you are using bathroom panels it is even easier. These can be used as the boxing and decorative finish in go.
  2. Fit bathroom furniture to cover the pipes. A concealed cistern unit and matching vanity units can be fitted together to cover the whole or part of the wall.

concealed cistern

Working With Soil Pipes

Modern soil pipes have a push-fit mechanism that utilises a rubber seal.

There will be a T junction on internal soil pipes in the room. This accepts the horizontal output pipe from the toilet. It is usually possible to pivot this T Junction. Doing this will enable the toilet to be fitted on a different wall. But there can be downsides. You could loosen the pipes or damage the rubber seals.

This option will not be available if the soil pipe exits through the bathroom wall.

There might be an option to re-route the pipe inside the bathroom. Or there might be an option to re-route the pipes on the outside wall when working with soil pipes. But there are lots of factors that need to be taken into account to see if this is viable.

Moving or re-routing a soil pipe is not an easy task so should really be left to the professionals.