I have thick solid stone walls, so struggle to get a signal to all parts of the house, let alone the my garden room. What I did was put a Pi with a 2nd z-stick in the garden room then shared the stick over the LAN - I think I followed this write up, and has been bulletproof so far Share Z-wave dongle over IP (USB over IP using ser2net / socat ) guide. This would obviously require you to have network in the garage, also the network viewer in habmin will break as it doesn’t seem to handle two zwave controllers
