The U.K. building regs. have a clause relating to a bathroom needing an openable window, the area of which I believe is either some minimum size or related proportionally to the volume of the room. If such a window is not feasible, or the bathroom has no window at all, then mechanical venting is required.
I've seen bathroom fans vented into the attic here, but I don't much care for the idea. Who wants all that water vapor deposited up there?
Range hoods are a mixed bag here: Some are vented outside, others are fitted with a charcoal filter and just recycle the air back into the room. Many of the latest models come with two sets of adapters and fittings to allow either installation method.
