Bathroom fan switch

Apparently one of the part F building regs mandates that a room with no opening window has to have a method of forced mechanical ventilation. Usually achieved by the use of a fan connected to the light. I know that was enforced 30 odd years ago when I built our bungalow
That's certainly what a lot of people believe, but I think it is, strictly speaking, a 'myth' - in that I don't think that Part F or the Building Regs (almost as short as Part P :-) ) says any such thing. Approved Document F does say something like that - but that, of course, is not a regulation or 'requirement'.
 
That's certainly what a lot of people believe, but I think it is, strictly speaking, a 'myth' - in that I don't think that Part F or the Building Regs (almost as short as Part P :-) ) says any such thing. Approved Document F does say something like that - but that, of course, is not a regulation or 'requirement'.
All I know really is that the building inspector wouldn't sign off until I had installed a fan in the windowless dark room that I had in the bungalow I built
 
All I know really is that the building inspector wouldn't sign off until I had installed a fan in the windowless dark room that I had in the bungalow I built


Quite so. I’ve seen builders have to add ventilation to extensions because they think they can ignore the guidance. No extraction, no completion cert
 
Apparently one of the part F building regs mandates that a room with no opening window has to have a method of forced mechanical ventilation. Usually achieved by the use of a fan connected to the light. I know that was enforced 30 odd years ago when I built our bungalow
I'm happy to be corrected but I didn't think forced ventilation in room without windows (other than high humidity rooms) came in very long ago - say 10 years, I almost feel I want to say 5 years but we all know about tempus fugit.
 
I'm happy to be corrected but I didn't think forced ventilation in room without windows (other than high humidity rooms) came in very long ago - say 10 years, I almost feel I want to say 5 years but we all know about tempus fugit.
Well that is what happened back then. Did different areas building control depts. have different regs.?. I thought they were a national thing rather than local govt. even over 30 years ago.
 
That's certainly what a lot of people believe, but I think it is, strictly speaking, a 'myth' - in that I don't think that Part F or the Building Regs (almost as short as Part P :-) ) says any such thing. Approved Document F does say something like that - but that, of course, is not a regulation or 'requirement'.
Yes, I was reading the Approved Document not the law, which said if you have windows which did not open, then you must be able to use the fan in a bathroom without switching on the lights, in fact it did not say the fan had to be connected to the lights in any way.

It really does not matter what document said it however, all I was pointing out was pointing out was at one point we were using double pole switches, which can easy get mixed up with intermediate switches.

It does not really matter if the law was a 'myth' it caused double pole switches to be used.
 
Would people have actually switched the fan on?
Would people have actually not switched the fan on if it also operated a light?

I've often heard the 2 pole switches mooted but what was the purpose?
 
Yes, I was reading the Approved Document not the law,.... It really does not matter what document said it ...
I think it matters quite a lot that people should not be given the impression that there is a legal requirement to do something when that it not true.
It does not really matter if the law was a 'myth' ....
The law is not a myth, but there are myths in relation to what the law actually says.
... it caused double pole switches to be used.
... I would say only very occasionally (despite the past discussions here about it). I don't think I've personally ever come across it.
 
I think it matters quite a lot that people should not be given the impression that there is a legal requirement to do something when that it not true.

The law is not a myth, but there are myths in relation to what the law actually says.

... I would say only very occasionally (despite the past discussions here about it). I don't think I've personally ever come across it.
I think the only time I've come across DP switches on light switches for fans has been for multiple rooms sharing a single in-line fan.


I've often heard the 2 pole switches mooted but what was the purpose?
I still can't work out why for a single room unless the light and fan are on different circuits/phases etc.
 
I still can't work out why for a single room unless the light and fan are on different circuits/phases etc.
I think that the suggestion (as proposed/discussed by BAS in the distant past) is that a DP switch would allow both light and fan to be switched on simultaneously (each using one of the poles) but, because there was thereby no connection between light and fan, if the light (hence fan) was 'off', one could switch on the fan (but NOT the light) by a separate switch/timer module/whatever.
 
I think that the suggestion (as proposed/discussed by BAS in the distant past) is that a DP switch would allow both light and fan to be switched on simultaneously (each using one of the poles) but, because there was thereby no connection between light and fan, if the light (hence fan) was 'off', one could switch on the fan (but NOT the light) by a separate switch/timer module/whatever.
Why would that need a DP switch?

Unless
...light and fan are on different circuits/phases etc.
 
Why would that need a DP switch?
Because if a SP switch were used to switch on both light and fan, the feeds to both lights and fan would obviously have to be connected together on the load side of the switch - and that 'connected together' would mean that nothing would be able to turn on the fan without also turning on the light.
 
One of the simplest control circuits for 2 devices
1777824944641.png

And this variation will allow switching off the fan with the light on
1777848308631.png
 
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Yes, that would also work.


Provided only that the fan switch was break-before-make, would you actually even need a DP switch if the light and fan were on different circuits/phases?
Possibly not, however I'd be inclined to do it that way.
If it's such a multiple room system where all 3 phases are likely to be used more than once I'd opt for a relay or opto isolator system to keep the mix of phases at devices to a minimum.
 

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