Why winter is condensation season
Condensation needs two things: moisture in the air and a surface cold enough to reach dew point. Winter supplies both. Windows stay shut, clothes dry indoors, heating cycles on and off — so humidity climbs — while external walls, windows and ceiling corners turn cold. The moisture in the warm indoor air condenses on the first sufficiently cold surface it meets.
Where the moisture comes from
A household produces far more water vapour than most people expect: cooking without lids or extraction, showers and baths, drying laundry on radiators and airers, and simple breathing — a sleeping occupant adds moisture to a bedroom all night. Without ventilation, that moisture accumulates day after day until the house is effectively storing it in its air and its fabric.
Why some rooms suffer more
Bedrooms top the list: they are occupied for long periods with doors closed, often heated least, and their external corners and window reveals run cold. North-facing rooms, rooms above unheated spaces and corners where insulation is interrupted by structure — lintels, ceiling edges, floor junctions — all condense first. That is also why mould colonises exactly those spots.
What actually helps
The measures that reliably reduce winter condensation work on one or both sides of the equation:
- Extract moisture at source: use kitchen and bathroom fans, keep lids on pans, vent tumble dryers
- Provide background ventilation: trickle vents open, airbricks clear, a window on the latch after showers
- Heat steadily rather than in bursts: steady background heat keeps surfaces above dew point
- Reduce cold spots where possible: insulation, and furniture kept slightly off external walls so air can circulate
When to get it assessed
If you are ventilating and heating sensibly and condensation or mould persists, something else is usually contributing — cold bridging, failed extraction, insulation defects or occasionally a separate damp problem masquerading as condensation. A condensation assessment measures the actual conditions and identifies which factors are doing the damage.
Need this looked at properly?
If this sounds like your property, a proper investigation will tell you which cause you're actually dealing with.