Ventilation

Building Regulations (Part F) require adequate ventilation in bathrooms and kitchens in new work and renovations, which in practice usually means a mechanical extractor unless there's an unusually large openable window. For an existing property without one, it isn't retroactively enforced, but the condensation and mould problems that follow from inadequate ventilation are exactly what the regulation exists to prevent.

A simple extractor fan removes moist air from one room (typically a bathroom or kitchen) and expels it outside; MVHR (mechanical ventilation with heat recovery) is a whole-house system that continuously extracts stale air and supplies fresh filtered air throughout the property, recovering most of the heat from the outgoing air in the process. MVHR suits a well-insulated, fairly airtight property far better than a leaky older one, where isolated extractors usually make more practical sense.

If the mould is genuinely caused by inadequate ventilation (rather than a leak or rising damp, which is a different problem entirely), a correctly sized and positioned extractor that's actually used consistently will stop new mould forming — though existing mould still needs treating and removing, since the fan prevents recurrence rather than cleaning what's already there.

Considerably quieter than fans from even ten years ago — most modern bathroom extractors run at a level that's barely noticeable, which also means people are more likely to actually leave them running long enough to clear the moisture rather than switching them off immediately out of irritation.

For a standard house, no — external vents for extractor fans are generally permitted development. The exception, as with most external work, is a listed building or a property within certain conservation area restrictions, where even a small external vent grille can need a sense-check before installation.

A simple extractor fan needs an occasional clean and, eventually, a motor replacement every several years; an MVHR system needs its filters checked and changed roughly every 3-6 months (more often in dustier or high-pollen periods) to keep working efficiently, which is worth factoring in as an ongoing task rather than a fit-and-forget system.

This usually means the extraction isn't keeping pace with how much moisture is being generated (cooking, drying laundry indoors, showering) relative to the room's ventilation capacity, or the extractor itself is underpowered or poorly positioned for the room. It's worth having the actual airflow assessed rather than assuming a bigger fan is automatically the answer — sometimes the fix is about positioning or usage habits as much as equipment.