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and most roof shingle manufacturers
prohibit the use of attic fans with
upper passive ventilation components.
As previously noted, attic fans typi-
cally do not run in the winter months.
Without any upper passive ventilation
to allow warm moist air entering the
attic from the occupied space below
a means to escape. This creates
conditions conducive to the formation
of condensation on cool surfaces
that are in contact with the exterior.
Condensation and moisture can lead
to the formation of microbial growth,
more commonly referred to as mold.
Furthermore, without proper ven-
tilation in the winter months, the air
temperature within the attic space will
be significantly higher than the exteri-
or air temperature. In the Northeast,
this is a primary cause of ice dams.
Ice dams occur when the warm air
in the attic causes the temperature of
the roof to rise above freezing. As the
snow on the surface of the roof melts,
it travels down the roof until reaching
the eave and gutter, where tempera-
tures remain below freezing. As the
water re-freezes at the eave, it creates
an ice dam. As the cycle continues,
water traveling down the surface of
the roof begins to back up the roof,
under the roof shingles where it can
infiltrate into the attic space resulting
in leaks to the interior.
Another issue that has been identified
with attic fans is their tendency to pull
conditioned air out of the occupied
space of the home. In the summer
months, drawing cool air from within
the home into the attic results in energy
ATTIC FANS...
from page 22.