However, the DOE recommends that attics in southern homes be insulated with at least 13 to 14 inches, or R-38, of insulation. Northern homes should have 16- to 18-inch thermally insulated attics or with thermal insulation. If your home doesn't have the recommended thickness, you may want to consider adding more insulation. At that point, it would be better to give up certification and lower insulation levels, since manufacturing that amount of insulation produces more emissions than would be saved over the life of a home.
The truth is that the insulation levels of the Building Code were not decided by great minds who were wondering what the “ideal” amount of insulation. Installing additional insulation in an older home when renovating can be a great idea, but when insulating exterior walls from the outside, be careful to do it right. It would have been economically and ecologically better to install only 8 inches of subslab insulation, regardless of your windows. In terms of insulation, it goes something like this: if you live in a cold climate and currently have a 2 x 4 wall with fiberglass insulation and you plan to add two inches of rigid cardboard insulation, the ROI could be 5 years, by choosing a random number.
It's as simple as this: adding an inch of insulation to a wall that only has an inch of insulation is definitely worth it, in any climate. That is, there is a balance point where generating heat is actually better for the environment than buying and installing more insulation. What I mean is that the money it costs to buy these insulating T-studs could generate greater energy savings if they were applied to an additional inch of insulation throughout the entire wall, by example.
