No working electrical extraction, no trickle vents, lots of moisture from the shower, and hey presto, black mould. We see this in almost every job we complete with tenants shutting trickle vents, closing every window in the house, and turning off the extractor fan because it's noisy and annoying.

I suppose it could be worse than noisy and annoying with black mould in your lungs.

We've also seen trickle vents covered in sellotape and even one job where the tenant had shoved paper into the vents to stop the draft.

Take black mould seriously. Never turn off extractor fans at the isolation switch unless there is an issue. If they stop working or make a strange noise report it. Kill mould spores as they appear in your cleaning routine and don't let them get rooted. Keep the front and back window locked and on the latch and open all trickle vents to ensure airflow across your home.

This job required the mould to be cleaned off, sanded back to kill the roots, and painted with specialist paint to try to stop this from happening again. The problem will return if the new tenants shut the windows and turn off the extractors.