We have a couple of hives in our roof, and when I phoned the local Bee Keeper's Association I asked them what to do about the ones in the roof.
Apparently, the best (and most bee friendly approach) is to find the entrance to the "roof hive" and then set up an empty hive as close as possible. Once you've done this, you can block the entrance to the "roof hive" using a tube containing some kind of wire mesh. The idea is that the bees will be able to escape the "roof hive" via the tube but they won't be able to find their way back in and they'll slowly begin to colonise the new hive instead. After a month or so almost all of the bees will have transferred to their new home and you can move them to a safe location.
I'm not sure how you would go about it in detail but it might be worth a try? Almost certainly better than gassing them.
We have a couple of hives in our roof, and when I phoned the local Bee Keeper's Association I asked them what to do about the ones in the roof.
Apparently, the best (and most bee friendly approach) is to find the entrance to the "roof hive" and then set up an empty hive as close as possible. Once you've done this, you can block the entrance to the "roof hive" using a tube containing some kind of wire mesh. The idea is that the bees will be able to escape the "roof hive" via the tube but they won't be able to find their way back in and they'll slowly begin to colonise the new hive instead. After a month or so almost all of the bees will have transferred to their new home and you can move them to a safe location.
I'm not sure how you would go about it in detail but it might be worth a try? Almost certainly better than gassing them.