You "can" use it outdoors sure, just don't expect it to last long. Any 5E cable will be shielded to some extent. They way you want to properly run ethernet cables is through a tube dug underground http://archive.slickdeals.net/showthread.php?sduid=0&t=766350
If the 2 areas are on the same power block, you may be able to use powerline ethernet, although that is a bit touchy to setup and get a good signal over.