Why condensation and mould keep coming back after cleaning

What causes condensation in the first place

Everyday activities like cooking, showering and drying washing indoors release significant amounts of moisture into the air, and if that moisture is not extracted or ventilated out, it circulates until it finds a cold surface to condense on. Older homes with solid walls and minimal insulation have more cold surfaces than a modern, well-insulated build, which is why condensation is more persistent in this housing stock.

Reduced ventilation is often a contributing factor too. Draught-proofing carried out without adding trickle vents or extractor fans can inadvertently seal moisture inside a home that previously relied on natural air leakage to keep humidity down.

Why South Devon properties are particularly prone

The region's higher year-round humidity, driven by its coastal climate, means the air itself often carries more moisture than an inland location, giving condensation more to work with even before internal moisture generation is considered. Combined with solid stone or brick walls that are colder to the touch than an insulated cavity wall, this creates ideal conditions for surface condensation in unheated or infrequently used rooms.

Holiday lets and second homes in the area add a further factor, since properties left unheated for periods between visits cool down thoroughly, and the first few days of reoccupation, with cooking, showering and heating suddenly introduced, often produce a spike in condensation before the building warms through.

• Higher ambient coastal humidity giving condensation more moisture to work with
• Cold solid walls providing surfaces where warm moist air readily condenses
• Draught-proofing carried out without adding replacement ventilation
• Properties left unheated between periods of use, then rapidly warmed
• Furniture placed hard against external walls restricting air movement

Telling condensation apart from rising or penetrating damp

Condensation typically appears on cold surfaces such as window reveals, external corners and behind furniture, and it responds quickly to changes in heating and ventilation, often clearing within days once conditions improve. Rising and penetrating damp, by contrast, tend to appear at specific heights or locations linked to the building fabric and do not resolve with ventilation changes alone.

Mould linked to condensation is usually black and surface-level, wiping off relatively easily, whereas mould linked to a genuine damp source often recurs alongside visible staining, salts or crumbling plaster that ventilation changes will not touch.

What actually fixes it long term

Addressing condensation properly means reducing moisture at the source, improving extraction in kitchens and bathrooms, and ensuring background ventilation is adequate once a home has been draught-proofed. Where cold surfaces are the main driver, improving insulation on the affected wall, using breathable materials appropriate to the wall type, reduces the temperature difference that causes condensation to form.

In holiday lets and infrequently heated homes, maintaining a low, consistent background heat level between uses, rather than leaving the property to fully cool and then rapidly reheating it, significantly reduces the spikes in condensation that come with reoccupation.

When to act

Occasional light condensation on a bathroom window after a shower is normal and not a cause for concern provided it clears quickly. Recurring mould in the same spot, especially if it returns within a couple of weeks of cleaning, indicates an underlying ventilation or insulation issue that is worth addressing properly.

If mould is spreading beyond a small patch, appearing in multiple rooms, or is accompanied by a persistent musty smell, it is worth having the ventilation and insulation of the property reviewed rather than continuing to clean it away.

Common questions