Can you add furring to 2 x 4 walls to hold 2 by 6 insulation?
...to it just be sure it's ready to last into the future. If you do recieve a lot of snow and it is a 2x4 wall on 24" centers for example, you may want to take advantage of that added 2 inches of wood to help carry a bit of the load if necessary. But, all this is simply a long-winded way to say, yeah, you can add 2 inch f...