Condo Media - September 2017 - 28

READY OR NOT, HERE IT COMES!
ICE DAMS EXPLAINED
The collision of warm air escaping from
attics with cold air on the outside creates a vicious cycle: The warm air heats
the underside of the roof sheeting and
melts the snow, which freezes, melts
again and re-freezes, creating a small
bump that gets larger every time the
cycle is repeated. That small ice bump
eventually forms a dam that blocks the
water, causing it to back up on the roof
and leak into the building.
The root causes of ice dams-inadequate insulation and ventilation in the
attic and/or inadequate ice and water
shield on the roof-suggest the strategies for avoiding them, Jack Carr, P.E.,
RS, LEED-AP, senior manager at Criterium- Mooney Engineers in Portland,
Maine, explains.

The best defense, he suggests, is a
properly ventilated attic, which will
short-circuit the heat-melt-refreeze
cycle by preventing moist hot air from
accumulating in the attic, so it never
reaches the underside of the roof sheeting. The old construction rule-of-thumb
called for 150 sq. ft. of ventilation for
every 150 sq. ft. of attic space. The current guideline doubles that-specifying
300-325 sq. ft. of ventilation for every
150 sq. ft. of attic space. "The more attic
ventilation, the better," Carr says.
If improving the ventilation isn't an
option, he suggests, the second-best
line of defense is to prevent the water
trapped by ice dams from leaking
through the roof.
Traditional building science assumed
that heat from overly warm attics could
shorten the life of asphalt shingles, but
modern research has proven otherwise.
"You still have to be concerned about
venting moisture from the attic," Carr
says. But if heat isn't an issue, you can
think differently about the installation
of ice and water shield on the roof. Instead of laying it in 18-foot-wide strips
from the outside walls-the traditional
approach-"you can cover the entire
roof and then lay the shingles over
that," creating what is a virtually impenetrable barrier. "There is no way water
can penetrate that surface," Carr says.
SMASHING, MELTING, HEATING
In a perfect world, most winters would
be mild, preventive measures would
be in place and effective for those that
aren't, and ice dams would never form.
In an imperfect world (the one we oc-

cupy), many condominium associations
will have to deal with the problem, if
they haven't already. There are a variety
of options to consider:
■ You can melt the ice dams with

chemicals. Calcium chloride is recommended most often. Ice-melt compounds including sodium, calcium and
magnesium are also effective, but they
can damage some secondary surfaces
and may harm plants on which the ice
dams melt.

■ You can treat ice dams with steam.

This is a new technique and highly effective, but also extremely expensive.
Some companies were reportedly
charging $750-950 per hour when
the ice dam problem was at its peak a
couple of years ago.

■ You can install automatic heat tapes

in gutters and downspouts. The tapes,
activated when ice dam risks develop,
are effective. But they are also unattractive, which seems why few associations are using them.

■ You can remove accumulated snow

from rooftops so it won't melt and
refreeze. This is the lowest-cost
solution, but it's not necessarily the
best choice: If not done carefully and
properly, removal could damage the
roof. Asphalt shingles, common in
New England, can get brittle in cold
temperatures. The rakes and shovels
used to remove the snow could break
off pieces of the shingles, creating
holes and potential leaks. The more

"The root causes of ice dams-inadequate insulation and ventilation in the attic and/or inadequate ice and water shield on the roof-suggest
the strategies for avoiding them."
-Jack Carr, P.E., RS, LEED-AP,
Senior Manager at Criterium- Mooney Engineers

CONDOMEDIA

Condo Media - September 2017

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