Why it happens
Large wardrobes and sofas restrict the movement of warm room air along a wall. An external wall can then become colder than the rest of the room. Moisture in the air can condense on or near that cold surface, supporting mould growth.
What to look for
Black spotting on wallpaper or the back of furniture, a musty smell and damage confined to a cold corner often fit this pattern. However, a local leak or penetrating moisture can cause similar problems, especially if the mark worsens after rain.
Check the room conditions
Consider whether the room is adequately heated and ventilated, whether clothes are dried inside, and whether extractor fans function. A humidity monitor can show trends but does not by itself identify why the wall is cold or wet.
Practical first steps
Move furniture slightly away from the wall if space allows, improve safe ventilation, deal with excess indoor moisture and maintain reasonable warmth. Check whether the wall has an underlying defect, especially if plaster feels wet or the problem persists.
Take mould seriously
Mould can affect health and needs prompt attention. Do not simply paint over it. Take particular care with extensive growth, people with respiratory conditions and situations involving contaminated materials; professional cleaning may be appropriate.
If the problem returns
Investigate cold bridging, missing insulation, moisture penetration and ventilation. A treatment that changes only the wall finish will not remove the underlying cause. Landlords should respond promptly to reports of mould and damp.
Keep dated photographs and notes of any changes. They can be useful when explaining the issue to a surveyor or contractor. If there is active water near electrics, an unstable ceiling, or a floor that appears unsafe, arrange prompt professional help rather than waiting to see whether the problem improves.
Need help from a local damp specialist?
Look for a suitable local professional and explain the symptoms clearly. You can use an external trade-matching service to request quotes; check credentials and the proposed diagnosis before agreeing to work.
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