I am trying to build a basement bathroom in the corner of the house. Where I am, basement insulation codes are R10/13. What is the minimum that I can do to frame and insulate a wall. The two methods that I thought of were 2" XPS (to get R10) + 2x3 furring strip + 0.5" cement board. That's 5". Maybe I could do 0.5" XPS for vapor barrier, then a 2x4 wall with batt insulation in the voids. That's 4.5". Is there anything wrong with that and/or is there a better way?