Why Condensation Is Such a Common Problem

Condensation forms when warm, moisture-laden air meets a cold surface and the water vapour turns back into liquid. In a modern home, we generate an enormous amount of moisture every day — cooking, showering, breathing, drying clothes — and when ventilation is poor, that moisture has nowhere to go.

The result is water droplets on windows, black mould on walls and ceilings, and a pervasive musty smell. Left unchecked, it can damage plaster, timber, and furnishings, and in some cases contribute to respiratory health issues.

Understanding Relative Humidity

The key measurement is relative humidity (RH) — the percentage of moisture in the air relative to how much it can hold at a given temperature. Ideally, you want indoor RH to stay between 40% and 60%. Above 70% and you're at significant risk of condensation and mould growth.

A simple digital hygrometer (available from hardware stores) lets you monitor RH levels in different rooms and identify where problems are most severe.

The Main Sources of Indoor Moisture

  • Cooking — boiling, frying, and using the kettle all release steam
  • Bathing and showering — a single shower can add significant moisture to the air
  • Drying clothes indoors — one of the biggest contributors, especially in winter
  • Breathing and perspiration — a household of four people generates several litres of moisture per day just by existing
  • Unflued gas heaters — combustion produces water vapour as a byproduct

How to Tackle Condensation: Practical Steps

1. Improve Ventilation

Ventilation is the single most effective tool. Open windows regularly, especially when cooking or showering. Fit trickle vents in window frames if you don't already have them. Extractor fans in kitchens and bathrooms should vent directly outside — not into the loft space.

2. Use a Dehumidifier

A refrigerant dehumidifier actively extracts moisture from the air and is highly effective in living spaces. For cooler rooms like garages and conservatories, a desiccant dehumidifier works better at lower temperatures. Running one in your most problematic room can make a noticeable difference quickly.

3. Heat Your Home More Evenly

Cold surfaces attract condensation. Keeping rooms at a consistent, moderate temperature — rather than letting them get very cold and then blasting the heat — reduces the temperature differential that drives condensation. Pay attention to unheated rooms like spare bedrooms, which are particularly prone to mould.

4. Insulate Cold Surfaces

Cold bridging — where heat escapes through poorly insulated spots like window frames, wall ties, or concrete lintels — creates cold spots that condense moisture. Improving insulation on external walls and fitting double or triple glazing eliminates many of these cold surfaces.

5. Adjust Daily Habits

  • Put lids on pots when cooking
  • Dry clothes outside when possible, or use a vented tumble dryer
  • Close bathroom and kitchen doors when generating steam
  • Keep furniture slightly away from external walls to allow air circulation

When to Seek Professional Help

If you've addressed ventilation and humidity and still see persistent mould — particularly on internal walls rather than just around cold windows — the problem may not be pure condensation. It could be a sign of penetrating damp, a failed cavity wall, or inadequate insulation that requires professional assessment.

Treating mould symptoms without addressing the root cause will only provide temporary relief. A damp specialist or energy assessor can carry out a proper survey and point you toward the right long-term solution.