Because mould around windows is highly visible and often looks serious, it’s commonly misdiagnosed as penetrating damp or faulty windows. Before assuming that, it helps to check how this fits within wider moisture patterns using a condensation diagnosis.
What’s actually happening at the window frame
Warm indoor air holds moisture. When that air comes into contact with cold window frames, especially around the edges of the glass and seals, the moisture can no longer stay suspended and turns into liquid water.
Window frames are usually colder than the surrounding walls, particularly overnight and in winter. Moisture settles there first, often invisibly at first, then repeatedly. Over time, this creates the damp surface conditions mould needs to grow.
Why window frames are especially affected
Frames sit at the boundary between indoor warmth and outdoor cold. Even modern double glazing can still have cold frame sections, particularly around corners and seals.
This is closely linked to the same mechanism that causes windows to be wet every morning. Where moisture regularly forms and isn’t fully dried out, mould spores are given the chance to establish themselves.
Why cleaning the mould doesn’t stop it coming back
Sprays and wipes remove visible mould, but they don’t change the surface temperature or moisture behaviour at the window. If condensation continues to form there, mould almost always returns.
This is why people often clean the same window frames repeatedly while the rest of the room appears unaffected.
How this relates to corner and ceiling mould
Black mould around windows is part of the same pattern seen with condensation and mould in corners and ceiling edges. In both cases, moisture is forming on cold surfaces rather than entering from outside.
The difference is visibility — window frames show the problem earlier and more clearly.
What usually helps first
The least disruptive improvements focus on reducing moisture build-up and preventing frames from staying cold for long periods. Keeping heating more consistent, allowing some controlled airflow overnight, and reducing evening moisture levels all help limit condensation forming at the window.
The aim isn’t to make the room colder or draughty, but to stop moisture settling faster than it can evaporate.
When it may not just be condensation
If mould spreads beyond the window frame into surrounding plaster, if the area feels persistently wet during warm weather, or if staining worsens regardless of ventilation or heating, further investigation may be needed.
In most cases, however, black mould around window frames is a condensation pattern — not a window failure.
Once that’s understood, it becomes much easier to address the cause rather than repeatedly treating the symptom.