Ask most homeowners whose utility bills are high what their homes need, and more likely than not they will reply “insulation”. One of the very first homes I audited was for a elementary school teacher who was a friend. She was going to buy more insulation for her home and thought she’d run the idea by me. I went over to her home and tested it with a blower door, and no amount of insulation was going to bring her utility bills down. It was one of the leakiest homes I’ve measured, still to this day. In other words, it had a lot of air moving through it. What most homeowners don’t realize is that insulation is only one side of the coin. Air sealing is the other. The two combined, an air seal and insulation, is what defines a good thermal barrier in the home, and yet most non-professionals only know about insulation.
A way to illustrate this might be the following example. Let’s say you want to go for a bicycle ride on a somewhat chilly day. Outside temperatures are in the upper 30’s F. If you put on your fleece jacket and hop on your bike, do you think you’re going to stay warm? Doubtful. Why? Because you know that cold air will sail right through that fleece rendering it next to worthless in keeping you warm. Put an outer windproof shell over that fleece and immediately you’ll notice a huge difference. In fact, it’s safe to say that you might quickly find yourself too warm. Not only is fleece (insulation) more or less worthless when air can circulate through it, by comparison it’s not even as important as the shell (the air barrier). If you’re riding that bicycle on a cold winter day and had to choose between a shell (air barrier) and a fleece jacket (insulation), which one would you choose?
Even still, in the building science classes that I teach for up-and-coming BPI home energy auditors, it takes awhile for this to sink in. Invariably when asked what can be done to an example home that is leaky, a couple of hands rise and blurt out “Add insulation”. This notion has been so ingrained in us by the pink, blue or beige insulation companies that it even takes some trained professionals awhile to get it. Oh, and that R-value printed on the insulation package? It was measured when the insulation was enclosed on all six sides in an airtight enclosure.
So the first common building science misconception is that insulation is all you need. While that may be true for a specific home here and there, it is most often incomplete. That insulation must be paired up and side-by-side with a good air barrier. Otherwise, that bike ride is going to be pretty darned cold.
This is a very good point and a very good metaphor. I remember I used to think insulation was the key. There is definitely more to energy auditing. I really enjoyed the BPI training course I took. So glad I did it. I love my job!
Really good article