Basements

Damp in Georgian basements

When assessing a symptom of a perceived damp problem in a Georgian basement, one point is fairly certain: Georgian basements were damp. The general absence of damp-proof courses and damp-proof membranes, and sometimes inadequate ventilation, provided ideal breeding grounds for wood-boring weevil, furniture beetle and both wet rot and dry rot: see the example below.

In respect to accommodation refurbishments, once a basement is tanked, lined, decorated and adequately ventilated, it should be habitable. Because of the generally high market value of Georgian properties, defects often arise from negligent work or poor design principles, rather than faulty systems. However, living in basements also requires good housekeeping skills to keep moisture under control. If ventilation systems are overridden or poorly maintained, condensation can lead to damp-staining and mould growth.

Earlier retrospective waterproofing techniques tended to rely on asphalt tanking to line the walls or bitumen membranes behind brick linings. These can fail if water pressures increase or joints fail. Basement waterproofing leaks are normally only discovered once the structure has been occupied, and while patch repairs are possible, they tend to be unreliable. Any remedial work or investigation is disruptive. The cause of damp needs to be diagnosed carefully, as it is important to isolate the effects of condensation. A normal moisture content of 40 to 60% is acceptable, and long-term monitoring can establish moisture patterns.

Basement waterproofing should always be considered as a 3-dimensional problem, and it is important to establish whether the system is required to provide or has failed to provide resistance to water pressure and whether additional controls on water vapour are also required.

Georgian basement: damp and dry rot

The walls in an uninhabited mid-terraced Georgian basement were damp, and timbers to the upper floors were becoming infected with early signs of dry rot. It was discovered that the untreated basement sat between two 'waterproofed' basements.


This had the effect that the untreated walls were acting as a 'sacrificial wick', causing them to become more damp than before. The walls had not become defective, but had become out of balance, due to the additional water resistance in the adjoining properties. All that was needed was to increase cross-flow ventilation, remove some modern plaster and paintwork, and leave the walls bare.


An interesting additional factor was that to the rear of the property was a canal but this had had no adverse effect on the property.