I cannot vouch for whether you are a bad boy and violate any building codes, BUT why not run PVP pipe outside? I'm not sure of your situation, but you could bury it 2 feet underground and be set for the most part. Shielding of cables is really only useful if your wire is going to be exposed to alot of magnetic interference(like your main power line to your house is going to be right next to your LAN cable). Indoors though, I'm not sure why you'd need PVC. I hope you aren't having to protect your cables inside your house more than outside!
Shielded twisted pair is really only used in Europe. North America doesn't see it.
I have never had a problem running standard Cat5 outside with the elements as long as its not exposed to the sun to degrade the exterior. Generally you want to run PVC piping or something to protect it from being easily cut, UV damaged, and moisture. Though, you have to cap off or seal off each end of the PVC so moisture doesn't collect inside.