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In past winters, homeowners from Baltimore to Boston to Billings have learned
about the damage caused by ice dams. In some cases, that knowledge came in the
form of a costly repair bill. In addition to gutter damage, water infiltration from ice
dams can also damage roof decks, insulation, exterior walls and paint, interior walls
and ceilings.
First
signs are wood rot, peeling paint and mold. but some of the damage from ice dams takes longer to
become apparent. Structural lumber soaked by infiltrating water, for example, becomes prime
feeding and nesting sites for insects such as carpenter ants.
That means several summers from now, homeowners may be facing carpentry repairs that are a direct
result of a previous winter’s ice dam problems.
As a roofing contractor, you have the opportunity to
help homeowners avoid the short- and long-term problems that can occur as a result of ice dams. That’s
why we’ve dedicated this report to the topic of ice
dams and how to eliminate them. We hope you find it informative and helpful in selling your roofing jobs.
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What Causes Ice Dams
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Considering the problems ice dams cause, it’s surprising
homeowners know so little about what causes them. In fact, it doesn’t take much. Only three conditions must
be present:
 1. A heavy snowfall — enough to
leave several inches of snow on a roof. The more snow left on a roof after
a storm, the greater the chances an ice dam may form.
2. Continuously cold temperatures.
A heavy snow followed by several days of 40’ temperatures probably won’t result in an ice dam. The air temperature must remain cold
enough for water to freeze. When temperatures
fall below 20’, conditions are especially favorable.
3. An under ventilated and poorly insulated attic,
factors that create what amounts to a “hot and cold roof” When those conditions are in place, here’s what happens:
• Heat escapes from the living quarters into the attic. The heat builds at the upper levels of the attic, eventually warming the
roof deck. Once the deck is warm, snow on the roof begins to melt. Obviously, if the sun breaks out following a snow storm,
melting at the upper roof is accelerated.
• Water runs down the roof until it reaches the area over the eaves. Since this area of the roof remains cold, the runoff from the
melting snow begins to freeze and the ice dam forms (along
with a more easily seen symptom of the problem, icicles hanging from gutters).
• As the dam builds, it begins to trap more snow melt, extending the height of the dam. But the
real problems begin when water begins to pool, backing up under the shingles. Once that happens, the damage can be extensive. In past winters, it’s been
reported that a homeowner had to drill holes in a kitchen ceiling to release water infiltrating from an ice dam. It was just one
of countless similar incidents.
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Solutions that ignore the problem.
If water was coming from a leaky upstairs faucet, the homeowner would call a plumber immediately. But
most homeowners don’t know how to deal with ice dam problems. In
fact, more often than not, they do the wrong things.
• They install heat tape along the eave area of the roof. It seems like a logical solution — after all, isn’t that where the problem
is? But heat tape doesn’t accomplish much; often all it does is push the location of an ice dam
further up the roof surface. (It’s also energy inefficient.) More generally, using heat tape creates
a condition just the opposite of what’s needed to eliminate ice dams. As we’ve seen, ice dams form
because there’s already too much heat on the roof. So adding more heat doesn’t solve the problem.
The goal is not to melt more snow, but to keep snow from melting in the first place.
• They scrape snow from the lower roof. In their
eagerness to eliminate an ice dam, homeowners
ignore the fact that scraping snow from a roof is also an easy way to damage shingles. It also can be extremely dangerous.
And it isn’t an effective approach to begin with. Because snow above the eave doesn’t cause ice dams.
The culprit is snow melting at the upper areas of a roof. They try to clean ice out of their gutters. For obvious
reasons, it’s a dangerous and ineffective approach. Icicles and ice-jammed gutters don’t cause ice dams.
In fact, they’re just another effect of a problem that starts with a hot-and-cold roof.
The only effective solution is a combination of high efficiency attic ventilation and adequate
insulation, ventilation and adequate insulation.
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How to Eliminate Ice Dams In Three Easy Steps
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1. Install adequate attic
ventilation. Because ice dams form
when a roof has warm upper surfaces and cold lower surfaces, the solution
is to equalize temperatures over the entire roof. Heating an entire roof is
impractical (and extremely costly), so the most effective solution is to create a
cold roof. To do that, you need a well designed attic ventilation system: it must supply
air flow along the entire
underside of the roof deck and it must have air intake vents evenly spaced along
the eaves. The most efficient system
(from both cost and performance stand-
points) uses ridge vents and an evenly
distributed layout of soffit vents. Cold
outside air is drawn into the soffit vents,
then washed over the underside of the
roof decking for the full length of the ridge. That’s critical, because this evenly
distributed air flow minimizes variation
in roof temperatures from peak to eave.
As a result, snow melt is reduced, greatly reducing the possibility that ice dams
can form.
2. Install adequate attic insulation.
Attic insulation serves two purposes. First, and most important, it minimizes heat
loss from a
home’s living quarters. Since that heat loss is a key factor contributing to the creation
of ice dams, stopping it at its source is critical. Second, adequate attic
insulation diminishes the energy impact
of having cold air flowing through the attic. How much insulation is needed to
be “adequate”? The answer depends on the region you live in. Check with your
local utility company for up-to-date
R-value requirements for your area. Be sure adequate amounts are installed around electrical fixtures and
wiring and plumbing chases. These areas often contribute to significant
heat loss. With existing insulation, also check for water damage and for areas
that have been compressed by foot traffic or stored objects.
3. If possible, install waterproofing shingle underlayment (WSU).
This is the last line of defense against infiltrating water. It’s important,
because even the most
efficient attic ventilation system may not be enough to eliminate all ice dams.
And a WSU barrier
can minimize and possibly eliminate water infiltration into the building
structure. Install WSU according to the manufacturers instructions. In general,
install WSU at least two feet above the
eave projection; many contractors suggest a three-foot barrier is even better. When working in
valleys, install WSU three feet on each side of the valley center.
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When installing attic ventilation,
you want to provide both maximum efficiency and out-
standing appearance. To do that, keep these points in mind
• Use ridge vents. Unlike standard roof vents, turbines or power vents,
ridge vents blend into
the roof line.
• Install ridge vents from end to end, along the entire ridge. Technically, that may provide more
airflow than minimally needed for adequate attic ventilation (but more airflow is always better than less).
The gain in finished appearance is well worth the few dollars more spent
for the
additional ridge vents.
• Install soffit or eave vents so air
flows between every rafter. That’s the only way you can
assure cold temperatures along the entire roof surface.
• Urge homeowners to install high efficiency ridge vents even when the
entire roof doesn’t
have to be replaced. Most homeowners don’t realize it’s possible.)
It's no more work than a
simple roof vent installation, but the gains in performance and comfort are
worth it.
• If you’re installing ridge vents on a roof with existing attic vents, be
sure to remove those
units. They would reduce the efficiency of the
new ridge vents.
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Getting
The Most From
Natural Air Flow
High
performance products such as Air Vent’s ShingleVent II’ and Multi-Pitch
FilterVent use an exclusive external baffle to provide high volume air flow, even in light
winds. That performance was demonstrated in tests conducted both at the University of
Illinois and Pittsburgh Testing Labs.
In one series of tests, air flow through four-foot sections of ShingleVent II and Multi-
Pitch FilterVent was measured. In a 1 5 mph breeze, these high performance ridge vents
produced air flow of more than 75 cubic feet per
minute per four-foot section of vent. By contrast, rolled mesh and corrugated style ridge vents
that use internal baffles — or no baffles could
not produce the negative pressure required to
pull air from an attic. At higher wind speeds,
some corrugated and rolled mesh vents
actually allowed air to enter the attic,
preventing any eave-to-ridge air flow.
Another important feature of both
ShingleVent II and Multi-Pitch FilterVent
is the internal weather filter. This feature
helps protect against the infiltration of dust
and insects into the attic.
To receive a copy
of the test results
mentioned in this
article, call
1-800 AIR VENT
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3000 W
.Commerce
Dallas Texas 75212
800-AIR-VENT
FAX: 800-635-7006
www.airvent.com |
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Try-Lock Roofing
Company
440 Northwood Drive, Tn. of Tonawanda, NY 14223
Phone: 716-447-1688 Fax: 716-447-1650 Email: Info@trylock.com
© 2001 Try-Lock Roofing Company |
All Rights Reserved. |
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