What causes rising damp and how is it fixed?

Genuine rising damp has a signature: a tide mark at a fairly consistent height above the floor, salt deposits at that line, and no obvious external source. It is real, and it is also the label attached to a great deal of damp that is actually something else.

The more common explanations

• Ground levels built up outside above the damp proof course, so moisture bypasses it. Paving, garden beds and new paths do this constantly.
• A bridged cavity, where mortar droppings or added insulation carry moisture across.
• Leaking plumbing inside the wall or under the slab.
• Poor surface drainage putting water against the wall repeatedly.
• Condensation on a cold surface, which looks similar and is fixed very differently.
• Blocked or missing subfloor ventilation in a suspended floor.

Investigate before you treat

Chemical damp proof course injection is expensive and it only addresses one specific mechanism. Applying it to a wall that is wet because the garden bed outside is above the damp course achieves nothing. Establishing external ground levels, checking for leaks and looking at drainage costs very little and resolves a large share of cases.