ALASKA
THERMAL
IMAGING LLC
ICE DAMMING
The Cause and Effects of Ice Damming | by Emmett Leffel
The effects of ice damming are numerous. Ice
damming can be extremely damaging to the
building and dangerous to occupants. Falling ice
is one of the most dangerous issues associated
with ice damming, second only to slips, trips,
and falls because of its frequent occurrence. I
have been through some store front entrances
in which I could not stay on my feet. Water
damage to interior and exterior finishes can be
another extremely expensive insurance claim
for a home or businesses. Worse yet, structural
damage to the roofing and/or building from
moisture intrusion and excessive weight loads
at the roof overhangs can result in significant
insurance claims and potential roof failures.
The actual causes of ice damming are as numerous as there are types of homes. It is not
caused by a roofing type or seasonal weather, and rarely is the lack of insulation or ventilation
the actual issue. In fact, too much insulation is more likely to cause ice damming than not
enough. While this information may be contrary to what most roofers and insulating companies
claim, it is true. I have seen garage attic spaces, in a 20 year old home, not have a piece of
insulation in it, with no history or indications of ice damming. Ice damming can also occur with
ridge vents or gable vents, neither is not necessarily better than the other. The recipe for ice
damming is simple: you need an attic bypass, snow build up, and a roof; sloping preferably but
not required. The outdoor temperature is a factor, but perhaps not in the way one would think.
Colder temperatures actually reduce the overall ability for roofing to create water, regardless
of snow build up. In climates where the heating
degree days are greater than 13000 and 14000,
as they are in the interior of Alaska, the condition
is less prominent. In these climates hoar frost is
more apt to form at the gable rake wall or gable
vent than are icicles and a dam at the eave. In
these extreme climates, builders would have us
believe that the lack of ice damming issues is
proof of their abilities, and this is only partially
true. The reasons for ice damming being more
prominent in one climate and not another are
simple: in order for the snow to melt at the
shingle surface, the attic bypass has to be
significant enough to raise the roofing, regardless
of type, near or above freezing conditions. In a
Image found @ sswc-mankato.com
ventilated attic space with outdoor temperature
well below 0 deg. F on a normal basis, there is rarely an attic bypass large enough to
overcome the dilution effect of building code prescribed attic or cathedral ceiling ventilation
requirements. For perfect ice damming conditions, similar to what we have seen in and
around the Anchorage area this year, we need snow, lots of it, a warming trend, say between
20 - 30 degrees Fahrenheit, and most importantly a construction defect or, as the energy
industry likes to call it, an attic bypass, whether you have an attic or not. The larger the attic
bypass, the larger the damming will be at the gutter leading up to the warming trend.
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Copyright 2008 - 2012 Alaska Thermal Imaging LLC All rights reserved.
Additionally, the more frequently we get snow
and changing weather patterns, the larger the
icicles can become, and the higher the cost
associated with the damage.
Common industry fixes typically speaking,
range from roofing type to design or
increasing ventilation. None of these actually
address the problem directly. You may have
heard statements that claim that metal roofs
or spray foam will fix ice damming. Each type
of repair is prescriptive based on the type of
contractor that is hired. A roofing company will
Biological growth in a cold
prescribe roof repairs just as an insulating
attic from condensation. All
company will suggest that insulation is the
roof sheeting had to be
solution to your ice damming. These types of
replaced
repairs are all band aids in the scheme of
things, in some cases applied where
tourniquets should have been used. Ice shielding does not change the condition(s) causing the
ice damming. In some cases, whole roofs are having a water proof membrane applied. This
can actually cause more damage to the structural integrity of the roof over the course of its life
because of moisture build up inside the attic. At least increasing ventilation potentially will
reduce the overall problem and insulation is always a recommendation but should be the last
improvement made before crawling out, not the first. I think Albert Einstein summed it up best
when he said: “You cannot solve a problem from the same consciousness that created it. You
must learn to see the world anew.”
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Copyright 2008 - 2012 Alaska Thermal Imaging LLC All rights reserved.
The assessment has to correctly identify
the attic bypass(es) or primary construction
defect that is causing the ice damming in
order to eliminate the damaging effects and
liability associated with ice damming. In fact,
eliminating the attic bypasses and adding the
prescribed insulation for your climate is the
only way to achieve a dividend on the
investment in your home or business. As I
stated earlier, there are just as many causes
of ice damming as there are building designs.
In order to correctly identify the right attic
bypass, a process of elimination has to occur
based on the existing conditions and roof
design. The extent and location of the ice
damming and history of the building are all
pertinent information. In some cases, the
integrity of the air barrier at the attic is not
the cause at all. Ice damming can result from
ducting or ventilation design to construction
defects or even the common scuttle hole like
the one depicted below. The right tools and
experience are needed to root out the
primary cause(s). The identification of one
cause of ice damming without applying the
appropriate investigative tools and process of
elimination is rarely sufficient in itself. Don’t
waste your time or money, stop shoveling
your roof and operating expensive heat
trace. Hire a professional building analyst
and start fixing your home today.
Attic Hatch
A ir leakage at - 5 0 pa
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Copyright 2008 - 2012 Alaska Thermal Imaging LLC All rights reserved.