London was once crossed by many small rivers flowing into the Thames, such as the Fleet, the Westbourne, the Tyburn and the Effra. Most were buried in culverts and sewers as the city grew, but the valleys they carved are still there.
Why old valleys matter
Low-lying ground along former river valleys can have higher groundwater, and the gravels and sands laid down by old rivers can carry water through the ground. Basements and cellars in these areas can be under more moisture pressure than those on higher ground nearby.
London Clay
Much of London sits on London Clay. Clay holds water against basement walls rather than letting it drain away, and it moves as it wets and dries.
Signs of a damp basement
- Damp or wet patches on walls and floors, especially after long wet spells
- Efflorescence: white salt deposits on brickwork
- A persistent damp, musty smell
- Failing old tanking, bubbling paint or blown plaster
- Water seeping in at the junction of the wall and floor
The answer: design for the ground conditions
A basement waterproofing system should be designed around the site, considering the water table, soil and how the space will be used. Cavity drain membranes with drainage and pumps are widely used because they manage water rather than trying to hold it back completely.
We are members of the Basement Waterproofing Association and have worked on basements across central London. See basement waterproofing in London.
