Suz wrote:
I first subscribed to this newsgroup about 4 years ago when we forst thought
about doing a renovation. Plans are now finally submitted and I'm making a
list of things to include for builder's quotes. The house will get a full
height extension to the side and a roof space conversion. With a kitchen,
two bathrooms and two bedrooms to sort I'll have loadsa questions in the
near future.
snip

I would be looking at an extractor timer, that's designed to time
extractor fans.
You connect up the extractor timer to a momentry switch, and a switched output from the PIR in parallel, to a momentary switch.
This way, you get an extra 5 mins (or whatever you set it to) whenever
the PIR triggers, or whenever the light is pressed). Run the fan from
the same circuit.

Easy alternative.
1W LED light, on all the time, that's enough to see where you are going
to turn the main switch on.