I am adding an addition, two floors, 10'X 30', Every one says I should go with 2X6's, The builder says its a waist of money but he will do as I ask, I live in the mountains of N.C. Which would be best in the long run 2X4 or 2X6. My gut says 2X6 but why spend it if I do not need it. I am told in some northern states that 2X6 is code when you have a second floor. Will this extra insulation be worth it. Any other tips would be appreciated. Thanks for your time.