Attic

How well a home is insulated will determine its comfort level. I have never seen an over insulated house. The majority of houses are under insulated, in many cases woefully so, built during the bye gone days of cheap energy.

The effectiveness of commercially available insulation is measured in terms of its R-Value, a figure that describes the relative resistance to the flow of heat through the material. Higher that number is the better.

99% of houses built before 1990 has R-11 exterior wall cavity insulation. That is because the structural frame is built with 2"x4" studs and 31/2" or R-11 of fiberglass insulation is all that will fit. In our area that has been determined as insufficient and the building code for new construction has been revised to require 2"x6" frame studs and R-19 or 51/2" of fiberglass insulation.

Since heat rises, the most important place to have adequate insulation is the attic. Fortunately it is also the easiest place to check and add insulation if need be. It is impossible to check the insulation value of a wall unless you have X-ray eyes but it is a safe bet that it is R-11 at best. In our area attic insulation of R-38 minimum is code. The Department of Energy recommends R-49. That is about 12” to 16" thickness of fiberglass batting or 18” to 24" of loose cellulose “blow in” type of material.

The attic must be adequately vented and should not have high humidity or signs of moisture accumulation. The building inspector will be sure to check all that. At a house that my dad was seriously considering, his home inspector informed us that the power exhaust vents from the bathrooms and kitchen range exhausted straight into the attic instead of out the roof. There were no apparent moisture damage but none the less a bad situation that needed to be rectified. The house was rejected.

http://www.ornl.gov/sci/roofs+walls/insulation/ins_16.html