I'm working on designs for 2 story modular construction that have a 2x6 ceiling on the lower level and a 9.5" I-Joist floor for the upper level. The lower level will have 8' ceilings in some areas and 9' ceilings in others. The 8' high areas will have 12" of air space between the top of ceiling joists and the bottom of floor joists for HVAC ductwork. In actual construction "walls" for that 12" gap will be created with 12" deep trusses.
My question is: How can I get a truss into that space in CA. When I create a truss it snaps to the top of the floor and It does not allow for changes to the elevation of the truss. The attached image shows what that space looks like where I need the truss as a "wall." I don't have to use a truss, the construction problem could be solved with a 12" high knee wall, But I don't know how to do that either! Can anyone offer a workaround for me?