Why Is There Mould Around My Windows? Common Reasons and Solutions

Mould around windows is a common headache, whether your home is old or new. The small spots you see around your windows can quickly lead to bigger problems like damaged frames or even health risks.

The good news? By addressing the root causes, you can prevent the fungi from returning. Here are some tips for maintaining mould-free and clean windows.

Is it normal to get mould around the windows?

Yes. You see, mould often forms when condensation collects on the glass and drips down onto the frame. It leads to dampness around the window frame. This creates the ideal environment for mould growth, particularly throughout the winter. After all, the greatest temperature differential between indoors and outdoors occurs at that time.

New homes are not immune to mould around windows, either. Did you know that modern airtight designs can trap moisture? Bad ventilation causes condensation, dampness, and eventually mould growth. Indoor activities like cooking and showering raise humidity levels as well.

What causes mould to grow near the windows?

So, now that you know it’s completely normal to have mould build up around windows, let’s lay out the question as it is, “Why is there mould on my windows?”.

Humidity is a major cause of mould around windows. Moist air collects on cool surfaces like window panes. It being there causes condensation, which breeds mould. So, maintain humidity level of 30% to 50%. Check with a hygrometer. If it’s too high, try a dehumidifier or improve ventilation.

Poor insulation can also cause mould. Cold surfaces near poorly insulated walls or windows attract moisture, especially in winter. Even new windows can develop mould. Upgrading to double or triple-glazed windows can help reduce condensation and prevent mould.

Leaky seals and frames are another common cause. Broken seals or gaps let water in, creating the perfect environment for mould. Check for drafts, gaps, or foggy glass. If you spot damage, fix or replace seals quickly to avoid bigger problems.

Common types of mould found around the windows

There are different types of mould on window sills. Each looks different, and they vary in terms of harmfulness.

1. Black mould (Stachybotrys chartarum) – It looks as slimy black or dark green patches. It develops when moisture penetrates broken double-glazed window seals. This mould is harmful and can lead to skin irritation, headaches, respiratory issues, and congestion of the nose. To save your health, take immediate action if you see it, especially in a bedroom;
2. Yellow mould (Aspergillus) – It grows on damp window sills and can also appear as green or black spots. It spreads quickly in humid areas and can trigger respiratory allergies or worsen asthma symptoms;
3. Green mould (Cladosporium) – Green mould appears as dark green or black patches, often on wooden frames in cool, damp conditions. While not as harmful as black mould, it can still irritate your skin and respiratory system;
4. Blue mould (Penicillium) – Blue mould shows up as bright blue or green patches. It thrives on water-damaged surfaces, including window sills. The spores it releases can trigger allergic reactions, especially in people with weakened immune systems;
5. Woolly mould (Alternaria) – Looks dark and fluffy. It’s often found on damp window sills and frames. It can cause allergic reactions like coughing, sneezing, and itchy eyes.

How do I stop mould from growing around my windows?

Mould types vary, and so do removal methods.

Clean the mould

Cleaning removes the mould and reduces the risk of it spreading. Here’s how to clean mould from around windows effectively.

DIY solutions

Specialised anti-mould cleaners

If DIY methods don’t work or you prefer a ready-made solution, use a window mould remover designed specifically for this purpose. Look for cleaners labelled safe for use on uPVC windows or other materials to avoid damage. Always follow the product’s instructions for the best results.

Call mould removal professionals

Sometimes, despite your best efforts, mould problems around windows can persist or become too severe to handle on your own. In such cases, calling mould removal professionals is the best solution. So, when to call the experts?

Provide sufficient ventilation in the mould-affected rooms

Good ventilation is key to preventing mould build-up around windows. It is so because it creates an environment in which mould cannot thrive.

Control humidity

Mould thrives in moist conditions, right? So, you need to optimal humidity levels.

Consider upgrading your windows

The prevention of mould growth can be greatly improved by upgrading your windows. Good windows with adequate insulation keep your house energy-efficient and minimise condensation. Thus, you may wish to think about:

Double-glazed windows are great for reducing condensation. They create an insulating barrier between the cold outside air and the warm indoor air. For even better insulation, consider triple-glazed windows. They’re a top choice, especially in colder climates, offering superior protection against condensation.

When choosing window frames, uPVC is a great option. It’s resistant to moisture and mould, low-maintenance and durable. Aluminium frames are another solid choice. They’re sleek, and weather-resistant. If you prefer the look of wood, just make sure it’s treated with mould-resistant coatings so it’s protected from moisture.

Repaint with anti-mould paint

This type of paint is packed with fungicides and biocides. It creates a protective layer that keeps mould at bay. But while it’s effective, it’s no magic fix. For the best results, you need to tackle the root causes of mould. That includes poor ventilation or high humidity. Only afterwards can you repaint.

To get started, clean the mould. You can use either vinegar, bleach, or a specialised mould remover. Make sure the surface is completely dry. The trapped moisture will only make things worse. Remove old, peeling paint and fix any plaster damage around windows with filler. Sand smooth before painting.

For the best protection, go with at least two coats. Once the paint is dry, focus on maintaining the area. Keep the room well-ventilated and manage humidity levels to make the paint’s mould-fighting power last longer.