I remember the guidance notes on intermittent extract fans in the Approved Document for Part F a few years ago were pretty badly worded, to the extent that it was hard to interpret what they were actually suggesting. Pulling up the current version, it looks as though there have been some changes from what I recall, but the part about timers is still somewhat vague:
In a room with no openable window (i.e. an internal room) an intermittent extract fan should have a 15 minute overrun.
15 minutes from when? When the fan is first switched on? When the room becomes unoccupied? If linked to the light as per this suggestion -
In rooms with no natural light, the fans could be controlled by the operation of the main room light switch.
- from when the light is switched off? Of course, in practice with the standard timer fan linked to the light switch it would be the latter. And although the timer fan linked to the light switch has become all too prevalent in British bathrooms these days, even these guidance notes only mention it in passing as something which
could be done in rooms with no natural light, so I really don't understand why it's become such a popular method. And:
ericmark said:
it would seem non opening window then not permitted to have light switch as only way to switch on.
I don't see where the guidance notes say that. They suggest linking with the light switch in rooms with no natural light as a possibility, but I can't see anything which discourages linking with the light switch anywhere else (not that I think it's a good idea to do so).
As far as the actual requirements of Part F are concerned, I see there appears to be a whole lot more about testing and notifying commissioning there now, but the underlying requirement of what needs to be fitted is still just a fan which provides adequate ventilation. So long as you have a suitable fan with a switch to turn it on and off, that requirement is satisfied.
