Will your walls grow mould this winter?
Room temperature, humidity and the weather outside decide it. Enter your hygrometer reading to see the dew point, your wall's surface temperature and exactly which humidity keeps mould away.
- ✓Dew point and wall surface temperature
- ✓The exact humidity that keeps mould away
- ✓Solid brick, cavity or insulated walls
Condensation will form on this surface
12.3°
Dew point
11.1°
Surface temp
100%
Surface RH
- →Bring indoor humidity below 48% at 19°C — a £15 hygrometer tells you where you are.
- →Run bathroom and kitchen extractors for 20 minutes after use; dry clothes outside or in a vented dryer.
- →This surface is thermally weak — insulation (internal, external or cavity fill) is the permanent fix.
- →Tide marks, salts or damp after rain point to penetrating or rising damp — a different cause and a different fix.
Mould keeps coming back? Damp Check finds the cause from your photos in 48 h.
Start a Damp CheckQuestions
What humidity causes mould?+
Mould grows when a surface stays above about 80% relative humidity for several days. Room humidity can be a comfortable 60% while a cold external corner sits above 80% — which is why mould appears in corners and behind furniture first.
What is the dew point?+
The temperature at which the moisture in the air turns into water. If a wall or window is colder than the dew point, water forms on it.
Why does mould grow behind my wardrobe?+
Furniture insulates the wall from the warm room, so that patch of wall is several degrees colder and its surface humidity much higher. Move furniture 5–10 cm away from external walls.
Is this condensation or damp?+
Black spot mould in corners, on window reveals and behind furniture in winter is almost always condensation. Tide marks, salts or patches that get worse after rain point to penetrating or rising damp. Damp Check tells them apart from your photos.
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