ROMEX and THHN/THWN in a Circuit

[L+10]

For at least one of my outlet circuits my plan is to run ROMEX from the panel to 3 ceiling mounted outlet boxes; then to a junction box from which I'll run THHN/THWN in 1/2" conduit to the remaining wall outlets in the circuit.

This is a pole garage, and my plan is to finish the interior with thermax white face insulation with no dry wall. The plan is to locate the junction box in the attic space and run the conduit down the girts to the 4' level - then parallel to the floor along a girt and behind both the posts and the thermax.

Is this either a code or safety problem? Is there a cheaper approach?

 

[Stuart in MN]

As long as you'll still have access to the junction boxes from the attic (they can't be hidden behind walls or under insulation) you should be fine.