Recessed lights are one of the most overlooked sources of air leaks into attics. The best choice is to change old can bodies (1) for airtight insulation-contact-rated (IC-rated) models (see the photo at right) and then seal the rim to the drywall with foam or caulk. IC-rated lights that aren’t airtight can be sealed by covering the fixture with an airtight box made from rigid-foam insulation (2 and 3), metal, or drywall, or by sealing holes in the can body with spray-foam insulation (4).
Remember that non-IC-rated cans need an airspace around them and can’t come in contact with the insulation. Some sources recommend installing a sealed box over non-IC-rated cans, but recessed-light manufacturers frown on this practice.
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The best practice is to replace non-IC-rated cans with air-sealed IC-rated models.
