Hmm ... 'round here (Nottingham, New Hampshire USA) the babies (Little Brown Bats) are born in March or April and the "adolescent" bats start going out on their own the first week in July. Their wings are still growing, so they come home on different ones than they left with, and sometimes get confused (and end up inside my house). My nursery colony (still not into the bat house instead of the space between the ceiling and the roof) usually moves out to go to their winter quarters sometime in September (unless August gets too hot and they stomp off in disgust).

Bat houses, BTW, to attract bats should be annointed with what can only be called batshit soup. (Yeah, collect some of the fertilizer you'd rather have on your garden, mix it with water and pour it on the wooden bat house -- do NOT serve for supper!)

Good luck! And I really hope the experts in your neck of the woods come up with a solution so the colony can prosper and you can get a new roof as well!

Linn