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Ice dams on roofs damage thousands of homes every winter. Ice dams are
caused by warm air in the attic melting the underside of the snow on the
roof. The water from the melted snow then sheds down towards the roof eaves.
The temperature at the roof eaves is much cooler, however, and as a result
the water refreezes at the roof edges. As the water refreezes at the roof
edges, ice dams on the roof begin to form. Roof ice dams can become very
thick, up to several inches to even a foot. Once the ice dams form,
additional water from melting snow on the roof can begin to back up
underneath the lower shingles. |
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Eventually the water finds its way
into the home and down onto ceiling edges, and inside surfaces of exterior
walls. Dark spots form on the ceilings and wall paint begins to bulge with
trapped water. In addition, puddles begin forming on the floor.
The best defense for preventing ice dams on roofs starts back during the
construction of the home. Ice and water shield, for example, should be installed
along the roof edges and valleys, prior to the installation of the roof
shingles.
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In addition, the home builder can
increase the heel height of the roof rafters or trusses over the exterior walls.
By increasing the heel height, more space is available in the attic near the
roof eaves for supporting additional insulation without restricting air flow
from the soffit vents.
Also, the builder can extend the roof rafter or truss tails further out from the
exterior walls of the home so that any water that may get up under the roof
shingles will simply drip out the bottom soffit areas, and not into the home.
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Moreover, the home builder can make
sure there is sufficient attic insulation and ventilation so that the attic
temperature stays as nearly as cold as the outside air. The colder the attic,
the less likelihood of melting snow and ice dams on the roof.
Although these construction recommendations for preventing ice dams on roofs are
great Monday morning quarterback suggestions, they offer little help for those
who are currently dealing with roof ice dams. If ice dams already exist on your
roof, you have limited options, and climbing up on your roof and hammering them
off is not one of them. Chipping the ice dams will potentially punch a hole
through the shingles, cause them to tear, and/or remove some of the aggregate
from the shingles.
| Your best solution for removing ice dams is to place long
tubular socks or nylon stockings, filled with ice melt, over the ice dams
and up the roof line, effectively running the stockings perpendicular to the
ice dams. The socks or stockings hold in the ice melt so that it doesn’t run
off too quickly from the roof. As the socks become soaked, the snow melt
water becomes saturated with the ice melt, which then helps to melt channels
in the ice dams for the water to drain from the roof. Place a stocking every
few feet along the roof line to create a number of drainage channels in the
roof ice dams. |
Photo by Mark Donovan |
Before applying the snow melt socks onto the ice dams you may want to remove
some of the snow near the roof edge so that you can place the snow melt socks in
direct contact with the ice dam surface. Use a snow rake or snow shovel to do
this.
Note that working on ladders that are in direct contact with roof ice dams and
non-stable surfaces is extremely dangerous. Make sure the ladder is well
anchored to the ground and that it is leaning at a sufficient enough of an angle
to prevent it from kicking out on you or laterally sliding. You may also want to
call in a second pair of hands to help keep the ladder stable while working on
it.
As an alternative to the ice melt filled sock approach, and to avoid climbing up
on ladders, you may want to look for roof-melt tables that can be tossed from
the ground onto the roof. They work similar to the snow melt sock approach for
removing ice dams on roofs by melting drainage channels into the ice dams.
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