When looking at building a home or retrofitting an existing one insulation and windows should be considered first. The better a home is insulated the more you can save on an annual basis in heating costs and other utilities also. Code insulation is currently R-20 in walls and Energy Star Code is R-21 in walls, however it has been proposed to be R-23. Spray foam is a great option and offers R-7 per inch (for closed cell) and R-4.5 for open cell foam.
Taking a look at window upgrades is a valuable investment also. To figure the R-value on windows from a U-factor is simply the inverse of each other. For example a window with a 0.33 U-factor would have a 3.03 R-value (that is 1/.029). This makes a difference when there are many windows in the home; if you upgrade to a 0.27 U-factor you would now have a 3.7 R-value. The bottom line is all of the upfront investment spent on greater insulation and windows will save money over time since your heat loss in the home will be less and the home will be much more efficient.
