Damp wall (rising damp)

Damp walls described as rising damp involve moisture moving upwards through masonry from the ground, typically up to around one metre above the floor, often producing tide marks and salt deposits. While true rising damp is less common than is sometimes suggested, defective external drainage is a frequent contributory factor, particularly leaking gullies, broken downpipes, blocked underground drains and saturated ground around the foundations. In older London terraces with original clay drains and shallow footings, an underlying drainage defect can keep the surrounding soil at high moisture content year-round. Building Regulations Part C and Part H set out requirements for site drainage and damp-proofing in new and altered work. Engineers usually address common causes by carrying out a CCTV survey, repairing defective gullies and clearing blocked surface water drains.