Tip O' the Month

Recessed Lights

Recessed lighting fixtures are a popular choice for lighting homes and offices. Also known as "cans", these fixtures offer an attractive, if utilitarian, method of delivering light to a room. Designers and builders will often specify several of these fixtures in every room; the record number of cans found in a home in the United States is 444.

These fixtures are rarely sealed properly when placed in top story rooms. Early fixtures, because of the heat build-up from the bulbs, had to be left exposed in the attic with a minimum six-inch uninsulated space around them. Newer models are allowed to be insulated, but the cans are vented with perforations that allow air to pass back and forth between the conditioned living space and the unconditioned attic space. The problem with most insulation is that it is not an air barrier, but instead acts more like a filter, and allows air to pass through. This is true of all insulation products except sprayed foam.

Recessed light fixtures must be sealed. They should also be insulated, but only when protected by a large enough wood or drywall box to prevent overheating. Even a newer fixture with its tin box will require a wood or drywall box over top of the tin box to allow heat from the bulb to dissipate.

If you choose to hire Ashton Thermal for this project, we will use our Zerodraft (two-component polyurethane foam) sealant. However, this product is not generally available from hardware or lumber retail stores and must be obtained from an industrial supplier. If you plan to do the project yourself, you can choose either a one-component insulating foam sealant or caulking.

The idea is to create a perfectly airtight separation between the ceiling and the attic. Seal all the joints and seams in the box (this will also hold the pieces of drywall or wood together) and seal the bottom of the box to the ceiling. You will also need to seal where all electrical wires penetrate the box. After sealing, insulation can be blown or positioned over the box.

By following the above procedure, you have brought the fixture within the conditioned space of the building envelope. The attic will be drier and colder, the room will be warmer, and no drafts will come from the fixture.

Remember, you must perform this operation on every recessed can that penetrates into the attic, or there will still be air loss. If you are bulding an addition or a new building with cans in the upper floor ceiling, insist that each fixture is sealed in this manner. See our video demonstration here: