Condo Media - September 2015 - 41

Ice dams are primarily caused by
indoor conditioned air reaching the
underside of the roof sheathing causing
a cycle of melting snow developing an
ice barrier at the drip edge of the roof.
Further melting snow water will then

back up under the shingles or soffits
allowing water infiltration into the

interior of the unit. By the time this
happens, snow roof raking rarely helps
 often
and chipping away at the ice dam
causes damage to the roof surface.
Heating cables on the roof edge tend to
reduce the life of shingles and do not

address the reason the ice is forming
in
the first place.
 we
To solve the problem of ice dams,
must address its root cause. As stated
 warm
earlier, this cause is unauthorized
air in your attic or other roof-structurerelated space. You may ask, why your
attic ventilation system is not doing its
job in removing this heated air from the
attic spaces.
Typically, a unit's soffit and ridge
vent system (or other venting system)
is designed to do just that. Though
there's a possibility this venting
system is poorly installed or ventilation blockage has developed, this is
unlikely. The fact that ice dams are
developing provides sufficient empirical evidence the vent system is being
overwhelmed with heated air from too
much leakage of conditioned air into
the attic space.
To determine how much and where
this air leakage is occurring is where
infrared scanning and other energy
audit techniques come into play.
Today's infrared camera scanning
(or thermal imaging inspection as
it's often called) takes colored photographs of interior or exterior building
surfaces. These colors represent a
gradient in temperature interpreted
by a skilled infrared imaging technician to locate air leaks or even water
leaks because of the sensitivity of the
infrared camera.
The value of these images is directly
related to the quality of the camera and
the image interpretation accuracy to
the experience of the technician.

An infrared scan can reveal air leakage into the attic through missing or
misplaced insulation, air paths through
ceiling light fixtures and plumbing/
electrical penetrations, and HVAC
duct seam leaks.
With the current energy codes,
newer homes should have less than 4
percent leakage, while homes older
than five years old have on average
leakage of 20 percent.
Newer homes required to meet the
more stringent state energy codes have
air seal tests performed called "blower
door tests" measuring the loss of pressure and the turns of indoor air per
hour in the unit.
If an older condo complex has been
experiencing a rash of ice dams this
past winter, the approach to stop their
cause would be to visually inspect
the unit for obvious insulation and
sealing problems. Following this
inspection, an infrared survey of a

sampling of units should be conducted
to determine the location and severity
of thermal leakage. To make an even
more complete understanding of the
air leakage, a blower test could also be
conducted on selected units.
Often these tests can produce surprising results, but more importantly,
they will give specific info on how to
correct the air leakage problem through
better insulation and the installation of
air barriers. These improvements will
not only eliminate ice dams from forming but will create a more thermally
efficient home, thus reducing future
utility costs.

n JACK CARR, P.E., RS, LEED-AP, IS
SENIOR VICE PRESIDENT WITH
CRITERIUM-ENGINEERS IN PORTLAND,
MAINE. HE IS A MEMBER OF THE
CONDO MEDIA BOARD AND A
FREQUENT AUTHOR AND SPEAKER.

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41
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Condo Media - September 2015

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