Start with what you can see
Damp announces itself in a handful of ways. Find the symptom you have and it will tell you which of the four causes you are dealing with — and they need completely different repairs.
Before anything else: the four causes of household damp are condensation, penetrating damp, rising damp and leaks. Condensation is by far the most common and costs nothing to fix. The others involve water entering the structure, and no appliance will help. Each page below starts by telling the two apart.
Find your symptom
Condensation on windows
The most common damp symptom, and the most useful one — it tells you your indoor air has more moisture than your coldest surface can tolerate.
Black mold on walls
Cleaning it is the easy part. The reason it returns to the same spot is a surface temperature problem, and that is what most advice misses.
Musty smell
A smell is mold you have not found yet. It is the one symptom that appears before anything becomes visible.
Damp patch on a wall
Four causes, four completely different repairs, ranging from free to five figures. Getting the diagnosis right is the whole job.
High humidity in summer
The season where the usual advice is wrong. Opening windows on a muggy day imports water and your AC pays for it.
Dry air in winter
Entirely seasonal, easy to fix, and easy to overdo — over-humidifying puts water straight onto your windows.