ICE RELATED DAMAGE TO BUILDINGS
Charles C. Roberts, Jr., Ph. D., P.E.
Figure 1 shows the classic ice dam formation on the eave of a building. The weight
of the ice can cause gutter and eave damage. Normal drainage is blocked and can
cause water to back up between shingle layers, drain onto ceiling insulation and
wallboard as shown in Figure 2.
Figure 3 illustrates the process of ice dam formation. During the day when warmer
temperatures are occurring, meltwater drains down the roof toward the gutters. As
the evening hours arrive, the eaves, being more exposed, tend to be cooler than the
roof area. Meltwater freezes first in area of the eaves. This tends to dam water
flow from the roof, resulting in a build-up of ice, hence the ice dam. During the
warmer period, liquid water can pond behind the dam and enter the attic space
through the seams in shingles. The water then drains onto insulation and eventually
causes interior water damage. Buildings with poor ceiling thermal insulation are
more vulnerable to this condition since their attics are warmer, which encourages
the freeze/thaw cycling, a major ingredient in the development of an ice dam.
Some buildings are more vulnerable to ice dam problems by design as shown in
Figure 4. The roof on the left in the photo drains toward a valley near a
vertical wall. Water drainage from the large roof on the left is directed against the
wall. Any ice dam developing at the discharge end of the valley can cause water to
back up and enter the wall structure. Because of the large roof draining into the
valley, a large volume of water must be carried by the valley, making the wall
vulnerable to water entry. The wire heater helps prevent the ice build up but may
not be effective in all conditions.
Damage caused by ice dams includes detached gutters, roof structure damage,
deterioration, interior water staining, and ice impact damage at lower levels.
Personal injury can also occur from impact with falling ice as well as slip and fall
accidents relating to ice debris on walkways.
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