How condensation causes mould
Everyday life puts a lot of water into the air: breathing, showering, cooking, boiling the kettle, drying clothes indoors. When that warm moist air meets a cold surface like a window, an external wall or a ceiling corner, it turns back into water. If that surface stays damp for long enough, mould grows. Condensation is the most common cause of mould in London homes, especially in flats, older solid wall houses and homes that are well sealed with little airflow.
Signs it is condensation
- Water running down the inside of windows in the morning
- Mould in corners, behind furniture and along ceiling edges
- Worse in winter, better in summer
- Musty smell in wardrobes and on clothes
- Mould on the coldest walls, often north facing
Not sure if it is condensation or damp? Read condensation or damp: how to tell.
How we fix it
- Measure. Humidity and surface temperature readings room by room to find where moisture is building up and which surfaces drop below dew point.
- Treat the mould. Fungicidal clean, treatment and sealing of all affected surfaces.
- Improve ventilation. Humidity controlled extractor fans in the bathroom and kitchen, trickle vents, or a positive input ventilation (PIV) unit for the whole home.
- Deal with cold spots. Where a wall or ceiling is a cold bridge, we can advise on insulating that area.
- Habit plan. A short written plan for heating and airing that suits how you live.
Price
Mould treatment is priced per room from £350. Humidity controlled extractor fans start around £180 fitted. PIV units typically cost £650 to £950 fitted depending on the unit and loft access. No VAT added.
Questions people ask
Will a dehumidifier fix condensation?
A dehumidifier helps, especially for drying clothes, but it treats the symptom. Proper extraction and a steady background heat usually make a bigger difference long term.
Is condensation the landlord or tenant responsibility?
It depends on the cause. Lifestyle plays a part, but poor ventilation, broken fans and cold walls are building issues. See our guide who is responsible for mould.