Stephendnz:
Thanks for all the replies.. Actually what I really wanted to know was which was a better option running semi permantly.. could be on a timer.. or a controller.. Fresh air coming in or stale air extracting air out.. Maybe it could operate while they are out during the day..
And yes will put extractor in the bathroom.. will have to go in the window but no biggy...
Cheers for all the feedback
You can install extractors that vent through the roof cladding (not in the roof space) as well. Make sure shower extractor is wired to the light switch so they can't turn it off.