The post originally appeared on the Green Building Advisor Website.
Recently, I’ve been on a few energy audits and assessments where the homes were built or remodeled in the late 1990’s and early 2000’s. Electricians working in those times were installing the traditional recessed light fixtures, also known as recessed cans or pot lights. This type of lighting fixture usually doesn’t have any issues when installed inside the air and thermal boundaries of the building envelope but can be very problematic when they end up displacing insulation and interrupting the continuity of the air control layer. I’m going to discuss the pros and cons of this type of lighting as well as how we can improve the performance of a home that has existing recessed cans.
Recessed lighting was first used in commercial settings in the 1940’s. They quickly transitioned to the residential market. Even today, this type of lighting is widely used, though most builders now know not to use the traditional “can” where it interrupts the air control layer. Modern recessed cans are required to have labeling identifying whether they can be in direct contact with insulation, this rating is noted as “IC” or insulation contact, and a label will be found on the fixture housing. Non-IC rated recessed light fixtures are required to maintain a 3-inch clearance to all insulations. IC rated fixtures contain a temperature sensor or thermal overload that will interrupt power to the light bulb should the temperature rise above a safe level.
The traditional recessed light fixture has some sort of mounting bracket, often these brackets are adjustable so that they fit in 16- or 24-inch center framing. (Other mounting options exist.) They also contain a junction box where the household wiring is terminated. Junction boxes by code are required to remain accessible. This is accomplished in a recessed light fixture by removing the main can body from the mounting bracket and junction box. For this reason, you should not encase the fixture in spray foam. Not only does the spray foam make it impossible to remove the can body to access the junction box, (an electrical code violation) but also traps any heat produced by the light bulb. This often results in the thermal overload tripping and causing the light to shut off. (If you have a recessed light fixture that blinks or shuts off for several minutes, only to turn back on later, the temperature overload is detecting a high temperature. Often if you reduce the bulb wattage, or switch from an incandescent bulb to LED, the issue is resolved.)
Once the recessed fixture is installed, insulating and air sealing around the fixture needs to be accomplished. Let’s cover insulation first. As mentioned earlier, the fixture needs to be rated for direct contact with insulation. Batt insulation will need to be carefully cut to be in contact all the way around the fixture with an appropriate amount covering the top of the fixture. A blown insulation will typically fill in the voids around the fixture, then the loose fill or batt insulation can be mounded over the top. Both these methods work well when they are installed in flat ceilings. Cathedral ceilings can be more complicated. Limited space between the interior ceiling and roof deck may limit the amount of insulation that can be installed. I’ve been in homes where the recessed fixtures in a cathedral ceiling will melt snow on the roof. I’ve seen divots, and even bare areas on snow covered roofs caused by the heat a recessed fixture can produce when there is not enough insulation above the fixture.
The next issue is continuity with the air control layer. A vented attic will typically have air control at the ceiling. The drywall may be performing this task, or some sort of membrane or polyethylene sheet product will be installed above the drywall. Either way, these products need to be connected to the recessed can housing in some way. I typically see tapes connecting a membrane to the metal housing of the fixture. I’ve also seen sealant such as acoustical caulking used to create an airtight seal. This works for connecting the fixture to the air control product, but what about any holes in the recessed can themselves. The newer recessed fixtures have been improved in how much air can move through the metal housing, but there are still some air pathways that remain. The older fixtures were not sealed nearly as well, air movement through these fixtures is something I commonly see. I have more than a hundred photos showing air leaking through the fixture during blower door testing, of course, living in a very cold climate helps to identify these problem areas. Trying to air seal all those small holes are tough, for instance, the wire conduit between the light socket and junction box is made of flexible metallic conduit, a type of conduit that is not airtight, the fittings for securing the conduit are also not designed with airtightness in mind. And then there’s the junction box, full of different holes and a cover that needs to be able to open to access the electrical connection. All connection points between inside the can body and outside, in the attic space. There are alternate methods that are a better choice than attempting to seal all those small holes individually.
Testing a recessed can for air leakage. There is a method to confirm the amount of air that is leaking through the recessed can housing during a blower door test. By using a tool called a powered flow hood (a flow box could also be used but would be less accurate), the rate of air moving through the fixture can be measured. The video shows how this is done.
The fixture in the video was leaking 12.3 CFM and there where 8 in this home accounting for roughly 10% of the total air leakage of this home.
We know the older recessed light fixtures are a problem, how can we correct the issues without completely removing the ceiling finish or swapping out the fixture? There are a couple ways, one requires access into the attic space and the second can be completed from inside the home.
Addressing Recessed Cans in the Attic. Before light discs and the recessed light fixture looking ceiling lights became popular, I was installing site-built foil faced Polyiso boxes over the top of the recessed can fixtures, then sealing these foam insulation boxes to the drywall or in my case, poly sheeting. They were never perfect, getting electrical wires to fit tightly around the box, or if the recessed fixture was pushed tightly against an attic framing member, making the box completely airtight was tough. They were “kind of” working. There are other options, a few manufacturers have produced covers designed for air sealing recessed fixtures, Tenmat is one example. Much simpler than building the Polyiso foam boxes.
Addressing Recessed Cans in the Home. An option to improve air tightness for recessed cans that can be installed from inside the home is to use the LED bulb that is integrated into the trim. These retrofit trims are designed to replace the standard bulb. The trim’s design makes it more airtight than the traditional trim with a separate bulb, the trim often comes with a gasket to improve the air tightness to the ceiling finish material. To further improve air sealing, a caulk or sealant could be added between the trim and ceiling, just be aware, if, or when the bulb burns out, the entire trim needs to be removed and replaced. The additional sealant may make that simple process much more complicated. The bulb life for the combination trim and bulb in the photo is rated at 35,000 hours, years of service before replacement is needed.
Recessed lighting has come a long way from where we were even 10 years ago. It’s rare I see the traditional “can” being used in new construction today, most fixtures have been changed to light disks or the recess looking fixture mounted to a traditional electrical box. But we still have decades worth of old recessed cans in the existing housing stock. Knowing how we can improve the air sealing without a complete remodel and replacement of these existing lights can help to improve the comfort, operating costs, and maybe even the durability of existing homes.