Winter weather creates the perfect environment for mould growth. When cold outdoor air meets warm indoor air, condensation forms on windows and sills. Over time, that moisture can damage surfaces and encourage mould.
This article explains why mould is more common in winter, what property owners should look out for, and how to reduce the risk in residential and commercial buildings across London.
How winter conditions drive condensation
Condensation forms when humid indoor air touches a cold surface. Windows, being among the coldest parts of a building envelope, attract this moisture first.
According to Homebuilding & Renovating, window condensation is one of the most common causes of mould around frames and seals in winter. As warm air cools on contact with glass, water droplets form and settle, especially on single or older double glazing.
Research by the Air Infiltration and Ventilation Centre highlights that modern, well-sealed buildings can worsen this issue by trapping moisture inside. Without regular air exchange, the water vapour produced by everyday activities—cooking, showering, or drying clothes—settles on windows instead of escaping outdoors.
Patrick Ryan Associates further notes that buildings with poor insulation or “thermal bridging” around windows experience colder surfaces, which directly increases condensation risk.
Why windows become mould hotspots
Windows act as the perfect condensation point. Their materials – glass, metal or uPVC – cool faster than walls, and their frames and seals collect residual moisture.
Common causes of window mould
-
Poor insulation: Cold air seeps through gaps around frames, cooling nearby surfaces.
-
Leaky seals: According to Allround Glazing, perished or damaged seals allow moisture to enter timber or uPVC joints.
-
High indoor humidity: Best Home Services explains that relative humidity above 60% increases the likelihood of visible mould.
-
Infrequent cleaning: Dust, dirt, and organic matter act as a food source for mould spores.
The combination of moisture and warmth provides ideal conditions for growth, especially during long, cold London winters.
Risks for residential property owners in London
For homeowners and landlords, mould is more than a cosmetic issue. It can lead to structural damage, reduced indoor air quality, and health concerns for residents.
| Risk type | Impact on property | Long-term effect |
|---|---|---|
| Structural damage | Dampness weakens plaster, paint, and window frames | Costly repairs and redecoration |
| Health impact | According to ASHRAE, mould exposure contributes to allergies and asthma | Tenant complaints and potential liability |
| Energy efficiency | Persistent moisture reduces insulation performance | Higher heating costs and condensation recurrence |
These problems are particularly common in period homes, where single glazing and draught-prone windows are still prevalent.
Risks for commercial property owners in London
Mould around windows in offices, shops, and public spaces affects both appearance and performance.
According to Aeroseal, condensation in commercial buildings can cause staining, corrosion, and reduced visibility, undermining a building’s professional image.
Why it matters for facilities and asset managers
-
Building aesthetics: Dirty or mould-marked glass can discourage customers and affect brand perception.
-
Building performance: The Victorian Building Authority found that condensation can compromise insulation and increase maintenance requirements.
-
Regulatory compliance: Mould can breach workplace health and safety standards or indoor air quality benchmarks in lease agreements.
For facilities teams, ongoing inspection and proactive cleaning can prevent costly repairs and maintain compliance with hygiene standards.
Practical prevention strategies
Minimising mould risk means controlling moisture, temperature, and ventilation.
Clearview Doors recommends regular cleaning, adequate airflow, and insulation checks as essential steps for mould prevention.
Key prevention tips
-
Ventilate daily: Use extractor fans, trickle vents, or open windows briefly to let humid air escape.
-
Maintain steady heating: Avoid letting rooms cool too much overnight, as sudden warming increases condensation.
-
Monitor humidity: Best Home Services advises keeping humidity between 30% and 50% using dehumidifiers or smart sensors.
-
Inspect seals regularly: According to Allround Glazing, deteriorated seals should be replaced promptly to prevent water ingress.
-
Upgrade glazing: Prem Windows & Doors highlights that upgrading from single to double or triple glazing significantly reduces condensation.
For practical advice on tackling winter condensation, read How to stop condensation on windows in winter.
How regular cleaning helps prevent mould
Routine window and frame cleaning helps identify early signs of condensation damage and keeps surfaces free from organic build-up.
Our blog ‘How do weather conditions impact window cleaning results’ explains how changing temperatures affect cleaning outcomes and why winter maintenance is essential for building longevity.
At DOC Cleaning, we work closely with property owners, landlords and facilities teams to:
-
Inspect windows for moisture build-up or frame deterioration
-
Clean and dry sills and seals to prevent mould growth
-
Support energy and ventilation strategies for healthier interiors
-
Maintain professional presentation for commercial buildings
Get in touch
If you manage a property in London and want expert help tackling mould and condensation around windows this winter, get in touch.
Our team can assess your building, design a tailored maintenance plan, and help protect your property from costly winter damage.