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Damp & mould

Why does my loft have condensation and mould?

Black mould in the loft is almost always a ventilation problem. Here's what causes it and how to stop it coming back.

If you've spotted black spots on the timbers or felt in your loft, the usual culprit is condensation: warm, damp air from the home rising into a cold, poorly ventilated roof space, where it settles on cold surfaces.

Common causes

  • Bathroom or kitchen extractor fans venting into the loft
  • Insulation blocking the eaves and stopping airflow
  • Newer airtight upgrades trapping moisture in older roofs
  • Gaps around the loft hatch letting warm, moist air up

The fix that lasts

Wiping mould away only treats the symptom. The lasting fix is to treat the affected areas and correct the cause — improving ventilation, redirecting any vents to the outside, and making sure insulation isn't choking the airflow at the eaves. Done properly, it doesn't come back the following winter.

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