Raised floor assembly with plumbing lines question – GreenBuildingAdvisor

In the process of designing a mater bedroom/bath addition that will be elevated on a col. and beam system (due to grades on site). I believe I have proper air and insulation barriers in place for climate zone 6 with an elevation of 6,000ft (which makes for a typically dry air environment). I included a sealed chase within the floor truss cavity for plumbing lines with only insulation below the lines. The thought process is for the ambient temp in the room as well as tying the chase into the existing “open” adjacent floor trusses would relieve concerns of the line(s) freezing. The room will have a mini split for heating and cooling. See attached.

Questions:

Do I need the plumbing chase? 

Should I fill the entire floor truss cavity with insulation or leave some air space between the bottom of the floor sheathing and insulation?