Green Building Library
Advanced Air Sealing:
Recessed Lights
Recessed light fixtures rated “IC” can be covered with insulation, but that doesn’t stop heat loss from air leakage. Indoor air also carries water vapor, which can support decay organisms, such as fungus, on roof sheathing. This is especially true in vaulted ceilings that have minimal ventilation.
Leakage through recessed fixtures is only a problem when they penetrate outside ceilings. Leakage doesn't occur through lights installed in a ceiling with conditioned space above, as in the first floor ceiling of a two story house. Here are several lighting options that reduce air leakage.
Option 1 - Surface-mounted Fixtures
To avoid the leakage problem, use surface mounted fixtures when possible. Then you simply seal the electrical box.
Option 2 - Sealed Soffits
One way to stop leakage is to build a sealed soffit below the insulated ceiling, so the recessed light is effectively inside the building. For this to work, the ceiling above the soffit must be covered with drywall and the joints taped. That means the soffit will have to be framed after the drywall is installed, which could be a scheduling headache. Another option: plywood, plastic sheets or housewrap could also be placed above the soffit before drywall.
Option 3 - Tested Fixtures
The easiest way to limit air leakage through recessed lights is to buy a fixture that has been designed for that purpose. These fixtures are certified for air leakage under the ASTM E283 test procedure. Several energy codes and standards limit the acceptable leakage to no more than 2.0 cfm at 75 pascals pressure difference. Tested fixtures are always IC-rated. Choose a fixture that meets the air leakage standard because the housing itself is tight. Avoid fixtures that rely on specific trim units for their seal. Tested fixtures normally carry a label showing their compliance with codes and standards. Some manufacturers supply a gasket to seal the housing and to the ceiling drywall. If a gasket isn't provided, you can run a bead of caulk between the drywall and the housing.
