NEC 300.22 applies, and is moderately complex. You can access sections of the Code online for free at http://www.nfpa.org/freecodes/free_a....asp?id=7008SB. You should also check with your local building official, since local codes often differ from the NEC, and local codes are governing.
For ducts or plenums "specially fabricated to transport environmental air" only certain types of cable and/or conduit are allowed. You say no wires are in ducts, so you're OK here.
For stud cavities, it doesn't apply "where the wiring passes through such spaces perpendicular to the long dimension of such spaces."
From your post, it sounds like the wires go the long way, so your guess is probably correct.