Here’s a classic example of air-leakage around a recessed light fixture. The dirty insulation in this photo is from air leaking out of the house and being filtered by the fibergalss insulation before it exits the house. (Fiberglass makes an effective filter in this case!) In fact, insulation that’s dirty on the bottom is one of the clues we look for during a home energy audit. Leaks like this represents a lot of heat loss in the winter, and depending on wind or duct leakage it can also mean higher cooling bills in the summer. Fortunately, there are ways to effectively air-sealing around these fixtures. Add to my to-do list: we’ll put together a short video showing the problem and the fix.
You definitely want to address this before you add insulation! Even taking advantage of the insulation tax credit only makes sense if you make sure you air-seal first.
[Be sure to check out the video on recessed lighting which includes a discussion of airsealing.]