RayV wrote:

I don't have a copy of the NEC but I think you can only put individual
wires through conduit not romex.

Yeah, I did a lot of reading last night on the NG and other sources,
and I decided that I would just use conduit on the outside of the house
from the breaker box to the crawlspace, then tack the wires to the
floor joists. This way it's not part of a conduit system, but providing
protection to the wire, which is OK with the NEC from what I've read.
I'm planning on only putting a max of 2 12/2 Romex wires through 3/4"
thin-wall EMT, with a run of maybe 5 feet from the box to where the
wire will penetrate into the crawlspace.

The reason I'm wanting to combine overhead and subfloor circuits is
that I'm wanting to keep some confusion out of the mix. I'm planning on
having the outlets in all the rooms on AFCI and the lighting for the
rooms on another, normal circuit breaker. That way if the AFCI trips we
can still have light in the rooms, and vice versa. The Square D AFCI
breakers I got don't allow for 2 conductors to be directly screwed down
onto them, so I'm just going to combine the wires and run a pigtail to
the breaker, which my research here has led me to believe is OK.

Thanks for all the responses. This NG has been a great tool in helping
me get what I need to do figured out. :-)

-Nathan