Quick answer
If your bathroom has no opening window, an extractor fan is effectively required. Part F of the Building Regulations sets minimum ventilation for bathrooms, and an internal (windowless) room must have mechanical extraction to the required rate. Even with a window, a fan is strongly recommended to control moisture, condensation and mould.
What Part F actually requires
Part F of the Building Regulations covers ventilation in homes, and bathrooms are one of the “wet rooms” it pays particular attention to. The principle is simple: every bathroom needs a way to clear the warm, moist air a shower or bath produces, before it condenses on cold surfaces and feeds mould. How you achieve that depends on the room.
Where there is a suitable opening window, that can provide the ventilation. Where the bathroom is internal — no window — mechanical extraction is required, typically an extractor fan rated to clear at least a set volume of air (commonly quoted around 15 litres per second for a bathroom). In practice, because windows alone are unreliable in British weather, we fit a fan in nearly every bathroom regardless.
When a fan is genuinely required
- A windowless or internal bathroom, en-suite or cloakroom
- A new bathroom created where none existed before
- A wet room or shower room with no openable window
- Any conversion (loft, garage) forming a new wet room
When it’s strongly advised anyway
- A bathroom with a window you rarely open in winter
- North-facing or cold rooms prone to condensation
- Busy family bathrooms with lots of showering
- Any room already showing signs of black mould
Good extraction keeps a bathroom dry, fresh and mould-free — and protects your paint, grout and ceiling.
Required extraction rates and Part F guidance change over time. Confirm the current figures for your project with Plymouth City Council building control or a qualified professional.
Why ventilation matters more than people think
A weak or missing extractor is the single most common reason a bathroom looks tired within a couple of years. Trapped moisture goes everywhere it shouldn’t — blackening grout, peeling paint, lifting silicone, and rotting window frames and skirtings. We strip out a lot of Plymouth bathrooms where the only problem was years of poor ventilation. Spending a little on a properly sized, well-ducted fan protects everything else you’ve invested in.
It also matters for health: persistent damp and mould aggravate asthma and allergies. A good fan, ducted to outside (not just into the loft) and ideally with a timer or humidity sensor, quietly does its job every day.
How we ventilate a bathroom properly
Right size, right rate
We size the fan to the room and the regs, not whatever’s cheapest — so it actually shifts the air a shower produces.
Ducted outside
The duct runs to an external vent, never just dumping moist air into the loft where it causes its own damp problems.
Smart controls
Timer overrun or humidity sensing means the fan keeps running after a shower until the air is genuinely clear.
The fan is wired by our qualified electrician — see do I need an electrician for a bathroom — and positioned to respect the electrical zones. It’s a standard part of every full bathroom installation we do.
Frequently asked
Is an extractor fan a legal requirement?
For a windowless bathroom, yes — Part F requires mechanical extraction. For a bathroom with a suitable opening window the window can technically satisfy ventilation, but a fan is still strongly recommended.
What size extractor fan do I need?
A bathroom fan is commonly required to clear around 15 litres of air per second, with higher rates for some rooms. We size it to your specific room and the current regs.
Can I just open the window instead?
If the room has an openable window it can meet the requirement, but in practice windows get left shut in winter, which is exactly when condensation is worst. We almost always recommend a fan as well.
Does a wet room need extra ventilation?
A wet room produces a lot of moisture, so good extraction is essential. See our wet room installation page and our answer on wet room building regs.
No more steamed-up mirrors
Get your bathroom ventilated properly
We’ll size, fit and certify the right extraction for your room — so your new bathroom stays dry, fresh and mould-free for years.