Maybe it depends on your living destination. In Europe the signal strength is regulated by authorities. I know that there are outdoor Z-Wave antennas available (Link, German language), but I don’t know if this will solve the distance problem.
An unofficial solution could be to power up the signal strength by yourself (Link). But of course, this modification is not allowed in Europe!!!
(Edited, because incorrect)
Maybe a better better solution should be to use of dLAN devices to extend your LAN. With such devices you are able to connect devices in the garage via LAN and/or WLAN (dLAN from devolo).
But it’s possible that dLAN doesn’t work correctly in apartment buildings because of the several circuits. So you have to check it.
