Several mechanisms, one location
Damp appearing where a wall meets the floor is one of the most common things we are called to, and one of the least diagnostic on its own. At least six different mechanisms produce damp in exactly that position, and they range in cost from a morning's work to a substantial remedial project.
Bridging at the damp-proof course
In a solid wall the damp-proof course sits close to floor level, so anything that carries moisture across it shows at the junction. A screed laid over the damp-proof course, plaster continuing down behind the skirting to the floor, render tight to a raised path outside, or rubble packed against the wall in a subfloor void all do it. Removing the bridge is frequently the whole remedy.
Solid floors and their own damp-proof membrane
Concrete floors laid before membranes became standard, or where a membrane was never lapped into the wall's damp-proof course, allow ground moisture through the slab and out at the perimeter, where the floor finish and the skirting slow evaporation. The evidence is usually damp at the junction on several walls rather than one, and the floor itself reads damp.
Leaks below the floor
Heating pipes buried in a screed and water supply pipes running under a floor produce damp at the perimeter as water travels along the slab and emerges at the weakest point. A leak is often given away by a warm patch, unexplained water use, a pressure loss on the heating system, or damp that does not respond at all to weather.
Suspended timber floors and subfloor conditions
With a suspended timber floor, the junction is where the joist ends and wall plate sit in the wall. Blocked air bricks, spoil in the void, high external ground and a leaking service in the void all wet those timbers, and the damp shows at the skirting. Here the risk is not just decoration but decay in structural timber, so it deserves proper investigation.
And sometimes it is condensation
The bottom of an external wall is often the coldest part of the room, particularly where the floor edge is uninsulated and furniture restricts air movement. Measure the surface temperature and the dew point and the answer becomes obvious — but nobody can tell by looking, which is exactly why an inspection measures the room as well as the wall.
Limitations of general guidance
This article is general guidance. It cannot confirm the cause of dampness in a specific property. Recommendations should follow an inspection of the building, its external environment and its internal conditions.
Book an inspection