Twenty-five years ago, back when I was working full time as an electrician, recessed lighting was all the rage. I’ve put up hundreds of these air-barrier-and-insulation-disrupting light fixtures. In 2010 my career as an energy auditor began, and I started seeing the effects of those decisions: colorful thermal images that appeared during blower-door testing, air leaking around all those holes in the ceiling air barrier. So we started telling homeowners, contractors, and electricians that these lighting options were bad, that changing to another product was necessary. It took a while, but people (and manufacturers) got the message. It’s rare for me to see the old-style recessed cans used in ceilings with an unconditioned attic, although I do still see them on occasion between insulated floors and in ceilings under conditioned attics.

The trend now is to use disk lighting, fixtures that do not require large cans or even framing-mounted electrical junction boxes. They hardly displace insulation or interrupt the air barrier when installed correctly.

Unfortunately, I’m seeing a lot of these fixtures installed incorrectly. The photo below shows what I often see in the field, especially in renovations: a hole cut in the ceiling that penetrates the air control (and in this case, the vapor retarder). The bottom photo is of the same home, in the attic where the moisture had moved from inside the home to a cold, condensing surface. Bad news!

Planning for disk lights

The easiest way to install the light fixture so that the entire assembly is inside the conditioned space of the home is to do so when building new. If you…