An old friend who is in the planning phase of his new home asked me today about the advantages of framing exterior walls with 2X6 studs instead of the conventional 2X4 framing. Chris found the information informative and suggested posting the information that I conveyed to him. Much like anything that is considered an "upgrade" there is added expense. You can assume roughly $1 per square foot of additional wood costs, which include the studs, plates, and window jambs. So what is the advantage? Well, the 2X6 exterior wall framing creates a 5 1/2 inch pocket to install insulation over the traditional 3 1/2 inches. This roughly translates to achieving an R-19 rating over the traditional R-13. If you decide to go with 2X6's there are two things that I highly recommend to maximize the thermal efficiency of your home. First, a minimum 1" rigid insulation board should be applied between the stud wall and the exterior sheathing and you will approach an R-24 rating. Second, upgrade the blown-in attic insulation to an R-38 or higher as heat loss is greatest through insulated attic areas.
If you are interested to know how long it will take to recoup your investment, most experts agree that there is a 1-3 year period before the true cost savings exceed the initial cash layout. Scientists at the Building Research Council at the University of Illinois have published a study that indicates there are two important factors which determine the rate of payback. First you must calculate the number of heating degree days in the region of the country in which you live (this is available through the National Weather Service). If you live in an area with 5,750 degree days or more per year, your payback will be much faster. The second factor is elevation above sea level. For every 1000 feet gained in altitude there is 5% less heat lost to conduction.
Bottom line is that if you are building a home that you intend to stay in for years to come and are interested in maximizing your homes efficiency 2X6 exterior wall framing is worth the added expense. I'd recommend discussing the means and methods of the framing with your builder because as you can see there are ways to maximize your investment with very little added expense.