When foundations are built in clay or mixtures of clay and sand, underground water will be held in contact with the walls and will cause leakage, particularly after heavy rains. One of the simplest ways of draining the soil adjacent to the walls is to lay a line of aggie pipe around the base of the foundation and to then lead the pipe into the stormwater drainage system.

It should be carefully bedded in a layer of sand or small stones. The pipe should be laid as such to prevent clay or silt entering, and the space adjacent to the wall should be filled with gravel or crushed stone up to 500mm below ground level. Cover with top soil and so that it is at ground level. The backfill should be compacted to avoid future settlement.