Cellars and Basements


A common question is "how can I reduce damp in my cellar or basement?". The best approach depends on the seriousness of the damp and the planned use of the cellar.

If there is only a slight problem or you just need a place for storage or as an occasional workshop, then focus on stopping water getting to the ground around the exterior walls and maximising evaporation. Make sure the ground slopes away from the building. Use a French drain to carry away water that hits the walls. Check that your drains are not leaking; you can commission a survey using a camera or pressure testing equipment. Make sure that the cellar is well ventilated. A dehumidifier will reduce the moisture content in the air but will have little short-term impact on the moisture in the fabric of the building. Consider using an extractor fan to assist in the ventilation over the long term.

As for the floor, you may find that when ventilation is in place, it becomes dry enough not to need any other intervention. As an alternative, some form of suspended floor might be possible provided it is adequately ventilated underneath.

If the problem is more serious, or you want a much drier room, you really need a vented and drained cavity system with a 'box within a box'; i.e. a room built inside the cellar. The moisture coming through the cellar walls and floor is then collected and removed. If possible, this can be done with a drain. Otherwise a sump and pump approach is needed.

Avoid using sealants such as bitumen; these may appear to work in the short term but the moisture has to go elsewhere and may damage the brickwork.

sloping ground option

A sloping ground option, with a gutter or gully to collect water, draining to a pipe.

level ground option

Level ground option, with a gutter or gully to collect water, draining to a sump managed with an electric pump to raise the water to a drain. The pump can be triggered automatically by a float-operated switch.