"dean" writes:
I want it to go perpendicular to the floor joists, hanging down just
below them. Is this an OK scenario? It will exit through a 4" hole in
the wall. Do I need to protect the vent from anything? I'm just not
sure what the code requirements are.

Thanks for any tips,

Solid tubing rather than anything flexible is vastly preferred
especially on a long run like that. If you must use flexible, make
sure it's the silver stuff and not the plastic white crapola. And
whatever you have, make sure you clean it annually.

You local fire department would be happy to educate you further, as
dryer fires are unfortunately quite common.

--
Todd H.
http://www.toddh.net/