Condensation or damp? How to tell the difference

The quick test

Condensation appears high up and in corners: window reveals, behind wardrobes on an outside wall, the ceiling edge of a bedroom, the cold wall of an extension. It is usually black speckled mould, and it is worse in winter and after showers, cooking and drying washing indoors.

Rising damp starts at the bottom. A tide mark within a metre of the floor, salts on the plaster, skirtings and plaster failing. It does not care what the weather did last night.

Penetrating damp is localised and follows a fault — under a failed gutter, around a cracked sill, below a chimney flashing. It gets dramatically worse in driving rain.

Nine times out of ten, what we are called to look at in Hampshire homes is condensation.

Why condensation happens where it does

Mould is a physics problem, not a cleaning problem. Warm moist air is meeting a cold surface. Wherever the building is coldest, the moisture condenses first and the mould grows there. That cold spot is almost always a cold bridge: an uninsulated window reveal, a concrete lintel, a thin single-skin extension wall, a solid chimney breast, a floor over an open garage, or a loft hatch.

Wiping it off treats the symptom. Removing the cold surface removes the cause.

What actually fixes it

1. Find the cold surfaces. A survey identifies which parts of the room are genuinely colder than the rest, rather than guessing from where the mould is worst.
2. Insulate them properly. That includes the reveals and lintels, not just the flat wall — these are the exact spots people skip.
3. Give the moisture somewhere to go. Extraction in kitchen and bathroom that actually runs, background ventilation, and not drying washing on radiators in a sealed room.

When it is not our job

If the survey shows the cause is rising or penetrating damp, we say so and point you to the right trade. Insulating over a genuinely wet wall makes things worse, and we would rather lose the job than sell you the wrong one.