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WHAT ARE ICE DAMS?
Ice dams are formed when heat from the inside of a home escapes into the attic
and warms the roof decking during the winter. This heat, combined with heat
from the sun, can melt snow on the roof. Melting snow on the upper roof and
in the valleys then runs down toward the eaves as water. When it reaches the
cold eaves and gutters it refreezes. The continual thaw and re-freeze process
creates ice dams. The result is water backing up under the roof shingles or
behind fascia boards where it can soak through the roof decking or wall sheathing,
causing damage to attics, ceilings and walls.
ICE DAM DEFENSE
 There
are three ways to defend against the damage ice dams cause: insulation, ventilation
and water-proofing shingle underlayment. All three work together. Insulation
keeps heat from escaping from your home’s living space into your attic. Ventilation
removes the heat and helps keep the roof deck evenly cool to help prevent snow
from melting on the roof. Finally, waterproofing shingle underlayment, such
as WinterGuard™, is laid across the roof before roof shingles are applied. WinterGuard
is warranted against leaks from dams that do form on the roof. With existing
roofs, waterproofing shingle underlayment is only an option if you remove the
existing shingles or are building a new addition. Regardless, increasing the
insulation R-value in the attic is always possible and ventilation can usually
be added to your attic easily
.
INSULATION
An attic insulated to today’s energy standards with fiber glass insulation
minimizes heat escape through the ceiling, virtually eliminating the possibility
of snow melting and refreezing at the base of the roof. If your home was built
before 1980, chances are it needs more attic insulation. The amount of insulation
your house should have will vary depending on where you live, how your house
is built and many other factors including your lifestyle. Insulation levels
are recommended by geographic zones and are stated in R-values. R-value is the
resistance to heat flow of a material. The higher the R-value the greater the
insulating power. The following map and chart indicate recommended levels of
insulation by geographic area.
R-values on the chart represent CertainTeed recommendations for meeting today’s
energy standards. Department of Energy thermal recommendations and the Council
of American Building Officials Model Energy Code provide the basis for CertainTeed’s
insulation recommendations.
VENTILATION
The second thing to look for in your attic is the amount of ventilation that
you have. It is important to have ventilation in the attic so any heat lost
from the interior of the home is drawn up and out of the attic. Adequate attic
ventilation will help the roof deck stay cool. Another benefit of having your
attic ventilated is that it allows for moisture that rises into the attic from
things such as bathing, cooking and the laundry to escape. Unchecked moisture
can promote mold, mildew, and wood rot. There are two common ways to ensure
that excess moisture or heat can escape to the outside. One way is to use a
power or mechanical ventilation system. The other way is through a natural or
static ventilation system. A power ventilator is an electric powered fan installed
at the roof or gable that runs by a thermostat or humidistat when the attic
needs ventilation. Natural or static ventilation systems consist of simple vent
or covered openings in your attic. These are typically ridge vents, gable, eave,
or roof vents. Many ventilation experts agree that externally baffled ridge
vents combined with vented soffits are a very effective method for ventilating
an attic. Where older construction doesn’t permit ridge and soffit ventilation,
powered fans can be a good alternative. A properly designed ventilation system
must have both intake vents in the soffit or eaves at the lower part of the
attic, and exhaust ventilation such as ridge vents high in the attic at or near
the ridge. Typically, cooler dryer outside air enters through eave vents near
the attic floor, forcing existing moisture-laden or heated air out through vents
placed high on the roof or gable. By ensuring proper insulation and ventilation,
you will run less risk of the formation of ice dams and you will substantially
reduce the likelihood of damaging your attic components.
WATERPROOFING UNDERLAYMENT
If you are building a new home, or reroofing an older home, in addition to
the points on insulation and ventilation mentioned above, you should insist
that waterproofing shingle underlayment be installed before your roof shingles
are applied. As mentioned earlier; it is completely resistant to water and,
as such, is a critical last line of defense against leaks, preventing backed
up water from getting into your new home wherever it is applied. CertainTeed
WinterGuard™ is warranted to prevent water penetration for the warranted life
of the new asphalt shingles applied over it (up to a maximum of 30 years). While
shingle underlayment does not prevent the formation of ice dams, it will prevent
backed up water from getting into the house. Discuss shingle underlayment placement
with your builder. However; as a guide, the CertainTeed Home Institute recommends
that it be applied:
• Under metal flashing and counter flashing at every roof penetration.
• In areas where roof pitches change, in valleys, at joints at building additions,
and at water stops behind chimneys.
• Along the eaves and at short cornice projections.
SPECIAL CASES
Many new homes feature cathedral or vaultedceiling roofs and skylights. Both
present special cases for insulation that the CertainTeed Home Institute recommends
you discuss carefully with your builder. Insulation manufacturers like CertainTeed
have created high-performance fiber glass batts that are designed specifically
for cathedral ceilings to provide higher R-values per inch than standard fiber
glass batts. In the case of skylights, quality workmanship and attention to
detail are important in preventing ice dams and condensation which often lead
to leaks. To avoid problems, make sure your builder properly insulates around
the skylight and uses a moisture retarder to prevent condensation. In addition,
applying waterproofing shingle underlayment around the skylight opening is recommended.
For more information on any of these products, write to:
CertainTeed Home Institute
P.O. Box 860
Valley Forge, PA 19482
or call 1-800-782-8777
Also visit us at
www.certainteed.com |
