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Friday, January 16, 2009

Preventing Ice dams

The cold weather is upon us and brings with it some home problems that are specific to Northern cold climates. Ice dams can be seen in both old and new homes and if left unchecked can lead to severe structural damage.

What is an Ice Dam?
Generally deeper snow and colder temperatures increase the formation of ice dams.
An ice dam is an accumulation of ice that builds up along the edge of a roof. The eavestrough may be overflowing with ice and there may be icicles hanging from the edge.

What causes an ice dam?
Snow build up effectively acts as an insulator on the roof. Heat from the attic warms the underside of the snow and melts the bottom layer. This water then runs under the snow cover and down the roof until it hits a cold surface like the overhang, where it refreezes.
As the cold spell continues the ice becomes thicker.

Why is this a problem?
The ice build up acts as a dam for the water running off beneath the snow. This can cause a back up and the water has to run somewhere. In severe cases that means under the roof shingles soaking the roof sheathing, insulation, wood framing and possibly your interior ceiling. Uncorrected the water can cause serious structural damage.

Ice dams can be prevented by eliminating heat build up in the attic. The following steps combine to help keep the temperature inside the attic nearly the same as the outside temperature:

1. Seal openings that allow heated inside air to rise into the attic. The attic hatch is of particular importance. This should be insulated and weather-stripped. All penetrations of wiring, plumbing pipes and wood framing into the attic should be sealed with caulk or expandable foam insulation. The spaces around chimneys should be sealed with sheet metal and high temperature caulk.

2. Make sure that bathroom exhaust fans do not discharge directly to the attic. The exhaust duct should be insulated and the area between the frame of the fan and the ceiling sealed.

3. Improve insulation to slow heat transfer into the attic. Current recommendations are for approximately 12 inches of Fiberglass bat insulation (R38+) or equivalent blown in type.

4. Improve ventilation to cool the attic space and remove unwanted moisture. (Note: Make sure that you do not block soffit vents when adding insulation.) Passive type ventilation such as soffit vents, ridge vents and/or high level exhaust vents are best. Powered exhaust vents are not generally recommended as they can cause negative pressure in the attic drawing more warm air from the heated space.