Recessed lights are very beautiful in homes but they can also cause problems if not properly installed.
The first thing you should do before installing a recessed light is know whether or not the area is insulated or not. If the light is going in a non-insulated area you can use a non IC rated light. In case you will be covering the light with insulation you should use an IC rated light. IC stands for insulation contact. This means you can cover the light with insulation.
When you cover a light with insulation it doesn’t mean you are air sealing that light. The best way to know that you are air sealing the light is to build a box or purchase a can light cover. You will still need to foam or caulk the seams to ensure a good seal. (this includes sealing the box down to drywall)
If a can light is not properly sealed it can heat up and cause a stack effect. This can suck the heated air out of the living space. The heated air will carry moisture and when the moisture cools it will condense onto sheathing and trusses. There usually isn’t enough moisture to cause problems in well vented attics.
By installing a box around the light it will air seal and also help keep the light from overheating and shutting down. The box does need to have a 3 inch airspace around the light. One unsealed can light can lose $5 to $30 more per year of energy.