Focus on Energy Q&A

Q: I am interested in building a newer, smaller and more energy-efficient home. In my preliminary research, it seems as though there are a lot more choices when it comes to insulating a home these days. Could you explain the differences (pros and cons) between traditional fiberglass batting, blown-in fiberglass or cellulose and sprayed foam insulation in homes. Is one type better than another? – Jason Johnson, Unity

A: The heat loss for a typical building can be divided into three equal parts: 1) conduction loss through windows and doors; 2) conduction loss through walls and ceilings; 3) air leakage. We focus on the first two losses by referencing the “R” value of the window and door system along with the insulation in walls and ceiling. Air leakage loss has nothing to do with “R” value.

Plumbers and electricians tend to cut over-sized holes for their utilities, leaving air leakage openings. Here is where foam can play an important role. Caulking can also help, but a good job requires more labor effort. A nearly ideal wall would be made of 6-inch studs with 2 inches of rigid foam on the outside. All openings and cracks should be sealed with spray foam. Blown cellulose insulation from the inside is best. The foam on the outside is a sufficient moisture barrier – plastic on the inside is both needless and dangerous.

Answer provided by Dick Hill, retired emeritus professor of engineering at the University of Maine.