The majority of London houses were constructed without indoor bathrooms. Almost all have since had modifications to rectify this, but often at the cost of an internal room that was once living space. Modern homeowners looking for more space often realise that moving facilities like bathrooms, toilets and laundry rooms to a basement level is, on the face of it, a very good idea, freeing space in the main house.

For developers looking to convert houses into apartments it is often the only practical solution.

The problem with basement plumbing is that water doesn’t flow uphill. Whether you simply want to add a toilet to an old cellar or are developing a large new living space complete with bars, kitchens, bathrooms or even swimming pools the basic problems are the same.

Property Values

Adding a basement bathroom will certainly boost your property’s value, but converting a basement to a high enough standard doesn’t come particularly cheap due to the large number of technical hurdles – like lighting, access and drainage – that have to be overcome. In regions that enjoy large gardens and big skies the obvious directions to extend are outwards and upwards. In crowded cities where land isn’t cheap, downwards becomes a financially appealing option. This is why basement construction in London will continue to boom for years to come.


In some lucky cases, basement floor levels are still above the elevation of nearby drains and sewers. In this case installing sinks, baths or toilets is almost as straightforward as constructing them on any other floor, other than ensuring good seals where pipes exit through tanked floors or walls. The only additional device you might require is a backwater valve to ensure flooding sewers can never backflow into the building. Pressure assisted outflows are also available.

In the majority of cases, however, waste liquids have to be elevated to the floor level above to be connected into the building’s existing waste outlets. Fortunately technological advance has provided efficient and affordable pumps that can be relied upon to do this job, quietly and unobtrusively.


Waste water and even soiled water can be collected into tanks that are installed below basement floors and then pumped up into the house’s regular plumbing system. A common problem in basement construction in London is the significant ground water that has to be kept out (especially if you happen to be on the route of one of London’s many lost rivers). A similar solution is sometimes used to solve this problem too, with a subterranean tank and an automatic sump pump.

Toilets normally require separate systems from waste water and are called sewage ejectors, but the basic principle is much the same.

Basement floor excavation adds to the costs for a small conversion but is proportionally insignificant in a large new build.

Upflushing toilets

These require no tank beneath the floor, relying instead on an electrically powered macerator to pump waste directly to the floor above through a narrow bore pipe instead of the familiar wide soil pipe. Some models incorporate a separate tank for ordinary waste water, solving both jobs in one.