Ice dams usually occur after a heavy snowfall and several days of freezing temperatures. Warm air inside your home leaks into poorly insulated areas of the attic
and will warm the underside of the roof causing snow and ice on the roof to melt. The melted water will drain along the roof, under the snow, until it reaches the cold overhang. The overhang tends to be at the same temperature as the outdoors and the melted water will refreeze and form an ice dam and icicles. The ice dam can cause damage to the roof, which will result in water leaks to the inside
. Frequently the result will be a water spot on the ceiling under the roof damage.
What Causes Ice Dams