Recessed light fixtures can create a
variety of problems in insulated
ceilings or attics. These perforated
metal cans, operating at close to
200°F, act like tiny chimneys,
drawing moist indoor air up into the
ceiling cavity (see Figure 1). In cold
weather, the moisture condenses
against the roof sheathing, causing a
buildup of water or frost (which
eventually melts into water). The
wet sheathing can get blackened
from mold. In cathedral ceilings, the
water often drips back to the house,
staining the ceiling and finishes.
Recessed lights also hurt the
performance of attic insulation. The
hot fixtures cause convective loops
that seriously degrade the effective
R-value of the insulation
surrounding the fixture. This
problem is not well documented,
but research at Oak