DPC (damp proof course)

The layer. Groundwater rises into masonry by capillary action. A damp-proof course is a continuous horizontal barrier, laid in a mortar joint near the base of the wall, that stops it. Materials include bitumen felt, polythene sheet, dense concrete or mortar with a waterproofing additive. Under the floor slab, a separate damp-proof membrane does the same job and should join the DPC.

The stage. Nigerian builders use "DPC level" for the point in construction when:

• the foundation has been dug and cast;
• the foundation walls have been built up and the inside filled and compacted;
• the ground-floor slab (often called the German floor) has been cast;
• the damp-proof course has been laid on top of the walls.

From here the walls rise towards lintel level. Sellers advertise "land with building at DPC level" to show how far a project has gone, and contractors often take a staged payment at DPC.

Why it matters to buyers. A missing or broken DPC causes damp, peeling paint, salt marks and mould at the base of walls, especially in wet, low-lying parts of Lagos.

Selling land with a building at DPC. A partly built house can be a good buy if the work is sound and the design suits you. Ask for the drawings and the approval that the work follows, and have an engineer check the foundation before you pay.

Repairing rising damp. In an existing building with a failed DPC, specialists can inject a chemical damp-proof course or cut in a new one. Treating the cause is better than repainting over damp walls.

• Lagos coastal and low-lying areas (Lekki, Ajah, parts of the mainland): high water tables make a sound DPC and membrane essential; sand-filling and raised foundations are common.
• Drier inland areas: the same construction applies, but rising damp is less severe.