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When the snow that is in
contact with the warm roof surface begins to melt, due to the poorly insulated
and ventilated attic, the resulting water travels down towards the roof edge. As
it nears the roof edge, where the roof surface temperature is colder, the water
freezes and begins to dam. The situation is exacerbated with the approach of
night, and the associated colder temperatures. As the melting and re-freezing
process continues the dam becomes thicker and causes water to back up under the
shingles. Eventually the water backs up far enough that it literally gets behind
the backs of the shingles. When this occurs the water works its way onto the
wood roof sheathing, where from there it proceeds to find any hole or crack it
can find. Eventually it ends up as water stains on your inside ceilings or even
worse.
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Preventing Ice
Dams
The fundamental solution for
preventing ice dams is to maintain a cold attic space and roof surface
temperature. Consequently, it is extremely important to properly and
sufficiently insulate and ventilate the attic. The end goal should be to achieve
an attic air temperature that is nearly equivalent to the outside ambient air
temperature. If the outside ambient air temperature is at or below freezing, and
the attic temperature is above freezing, snow melt will occur on the roof
surface and ice dams will form.
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Properly Insulate
the Attic
Use at a minimum R-30 fiberglass batt
insulation in the attic between the ceiling joists. R-30 batt insulation is 9.5”
in thickness. In the process of installing the insulation make sure there are no
gaps around ceiling lights, bathroom fans or other mechanical equipment in the
attic.
Also make sure that the bathroom fans
are properly vented to the outside of the home. If they are not properly
ventilated they will send warm moist air into the attic which will lead to the
formation of ice dams. Improperly ventilated bathroom fans can also lead to the
formation of attic mold and mildew.
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Properly Ventilate
the Attic
It is important to make sure that any
heat that does work its way from the home’s main living space into the attic be
ventilated out of the attic as quickly as possible. To achieve this make sure
the gable vents, ridge vents and soffit vents are not blocked via insulation or
other obstructions. The use of attic rafter vents, along the edge of the roof
line can help to ensure proper airflow from the soffit vents into the attic
area.
New Construction –
Best Time for Preventing Ice Dams
During the construction of a new
home, or re-shingling a roof, there are a number of preventive steps that can be
taken to prevent Ice dams.
First, the longer the width of the
roof overhang over the exterior walls the lower the potential for water damage
to the home. Water damage is limited to only the exterior soffit area.
Second, when shingling a roof an ice
and water shield underlayment membrane should be used along the edge of the
roof, in roof valleys and around plumbing stacks, chimneys, and skylights. It
is applied directly to the wood sheathing prior to the installation of the
shingles. The membrane is designed to seal around the roofing nails as they
penetrate the membrane.
With these few basic preventive home
maintenance and construction tips you should be able to prevent ice dams and
their damaging effects this winter.
For more help on Shingling Your Home's Roof, see HomeAdditionPlus.com’s
Asphalt Shingle Roofing Bid Sheet.
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Asphalt Shingle Roofing Bid Sheet
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your roof won't end up with a blue tarp over it and a dumpster sitting in your
yard for weeks
as you wait for the roofing contractor to come back and finish roofing your
home.
How to Finance your Roof Project -
can help provide funds for your new home improvement project if financing is
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