Mould on windows and doors is a widespread issue in homes across the UK and Ireland, caused mainly by condensation, poor ventilation, and cold surfaces. At Fenbro, we help homeowners prevent and solve this common problem, protecting both their health and property.
In this article, you’ll discover the main causes of mould, how to prevent mould around windows and doors, and the best steps for effective mould removal.
What are the main causes of mould on windows and doors?
Mould typically forms due to a combination of excess moisture, poor airflow, and cold surfaces. Window frames, reveals, and seals are particularly vulnerable, as condensation frequently gathers there. The most common causes of mould are:
- Condensation — cold window or door frames cause warm, humid indoor air to condense on the surface. Click here for our article and find out how to stop mould on windows by tackling condensation.
- Poor ventilation — insufficient airflow prevents moisture from escaping, encouraging mould growth.
- Leaky seals — gaps or cracks in window seals let moisture in and create ideal conditions for mould formation.
- Thermal bridges — poorly insulated areas lead to cold spots and condensation.
- Incorrect heating habits — irregular or low heating can raise indoor humidity levels.
- Structural defects — damaged window frames, poor insulation, or faulty sealing heighten the risk of mould.
- Unsuitable building materials — materials that absorb moisture provide the perfect breeding ground for mould.
How do windows influence mould formation?
Windows play a huge role in managing moisture in a home. They affect airflow and the temperature of internal surfaces. Old or poorly installed windows can increase the risk of mould formation by allowing moisture to enter. Mould windows with single glazing or inadequate insulation are particularly problematic, as the temperature difference between inside and outside creates condensation.
Modern, well-insulated windows help rooms stay warmer and improve energy efficiency. However, even these can contribute to mould problems if they are badly fitted or used in an under-insulated building. Studies show that up to 80% of mould issues in homes stem from poor airflow and faulty window installation.
Why is condensation on windows problematic?
Condensation on mould windows can allow moisture to seep into frames, seals, or masonry. This is especially common in winter, when warm, moist air meets cold window panes and cools, leading to water collecting on the inside. This trapped moisture can penetrate frames or walls, creating the ideal environment for mould.
Depending on the type of window, the problem may vary:
- Single-glazed windows cool quickly and are most prone to condensation.
- Double or triple glazing with thermal breaks helps reduce therisk, as the inside pane stays warmer.
- Aluminium frames without thermal breaks can form cold bridges, where moisture collects.
How can mould be prevented?
Not just the type of windows, but also their installation, can contribute to mould formation. Professional installation is key to mould prevention. Avoid these common mistakes:
- Leaky connection joints — if windows aren’t properly sealed, moisture can get into the masonry and cause hidden mould growth.
- Lack of insulation around windows — when replacing old windows in poorly insulated homes, temperature differences can lead to condensation around reveals.
- Poor ventilation strategy — airtight windows reduce natural airflow. If you don’t actively ventilate, moisture can build up.
How to prevent mould around windows?
To minimise the risk of mould formation, take the following steps when selecting and installing windows:
- Choose well-insulated windows — modern, multi-glazed windows with thermally broken frames help prevent condensation.
- Ensure professional fitting — installation should meet RAL guidelines to avoid cold bridges or draughty joints.
- Ventilate regularly — open windows fully several times a day to release moisture. This is especially important in humid rooms like bathrooms and kitchens.
- Consider additional ventilation — if natural ventilation isn’t enough, trickle vents or automated ventilation systems can help.
- Keep rooms warm — consistent heating prevents cold surfaces where moisture could settle.
- Check wall insulation — if external walls are poorly insulated, replacing windows alone won’t solve the issue. Additional external wall insulation may be needed.
How can mould removal be carried out?
For smaller patches, the best mould remover is often 70% alcohol or methylated spirits, both of which are highly effective. Apply the alcohol directly to a clean cloth and wipe the affected area thoroughly. Let the alcohol sit on the surface for a few minutes to ensure the mould is fully killed, then wipe again with a dry cloth to remove residue. Avoid harsh chemical removers, as they may release harmful fumes. When tackling mould removal, wear gloves and a face covering to limit contact with mould spores. After treatment, thoroughly dry the affected area, as lingering moisture can cause mould to return.
To guard against future outbreaks, apply a mould-resistant paint or specialist sealant. If the mould infestation is widespread or has penetrated deep into masonry, it’s essential to call a professional for thorough treatment.
Preventing mould in the home – helpful tips
You can prevent mould formation by adjusting both your room layout and daily habits:
- Ventilate properly — air rooms several times a day (5–10 minutes each time). Avoid leaving windows ajar all day, as this can cool walls.
- Heat rooms evenly — maintain steady temperatures to prevent large temperature differences.
- Bedrooms & children’s rooms: 16–18°C
- Living rooms & bathrooms: 20–23°C
- Don’t dry laundry indoors — avoid excess moisture by drying clothes outside or in a well-ventilated room.
- Control bathroom humidity — after showering or bathing, ventilate well or use an extractor fan. Keep the bathroom door closed to stop moisture spreading.
- Reduce steam in the kitchen — open a window or use an extractor hood when cooking. Keep the kitchen door closed to contain moisture.
Conclusion
Windows and doors are crucial in managing moisture in your home. Choosing the right products, ensuring correct installation, and maintaining them properly will go a long way towards mould prevention. Modern, energy-efficient windows with strong insulation, combined with careful indoor climate control, can significantly reduce the risk of mould.If mould is already present, or if you’re unsure how to proceed, seek professional mould removal and treatment.
At Fenbro, we provide modern, energy-efficient windows, and our installers ensure expert fitting. Contact our team to learn more! With the right approach, you can enjoy a healthy, mould-free home for the long term.
FAQ – Frequently Asked Questions
How do I recognise mould on my windows?
Mould usually appears as black or greenish spots on window frames, seals, or reveals. A musty smell can also be a sign.
How often should I ventilate to prevent mould?
Ideally, ventilate rooms three to four times a day for 5–10 minutes. It’s particularly important after showering, cooking, or when several people are in a room.
Which Fenbro windows are best for mould prevention?
Double or triple glazing with thermal breaks is ideal. Windows with built-in ventilation can also help.
What should I do if mould has already formed?
For smaller areas, apply 70% alcohol or methylated spirits to a clean cloth and thoroughly wipe the affected area. Allow the alcohol to sit for several minutes to kill the mould effectively, then wipe the surface again with a dry cloth. Once the area is fully dry, consider applying mould-resistant paint to prevent recurrence. For severe cases, consult a professional for mould treatment.
