Ice Dams
As summer has come to an end and winter weather approaches, one of the most common problems we face every year in Minnesota is ice damming or icicles brought on when it snows. Many homeowners will experience leakage as a result of these “ice dams”.
What Is An Ice Dam?
When a sequence of weather conditions occur within a brief period of time, many Minnesota homeowners experience ice damming. Three things are required for an ice dam to form: snow, heat to melt the snow and cold to refreeze the melted snow into solid ice. Ice dams can form when as little as 1 or 2 inches of snow accumulates on a roof.
After heavy snowfall and several days of freezing temperatures is usually when ice dams occur. Warm air inside your home leaks into 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?
Poor attic insulation or air leaks inside the home that allows warm air to get into the attic. The snow melts when the warm air rises and raises the temperature of the underside of the roof. The melted snow runs down the warmed roof until it reaches the roof overhang that is not warm and is the same temperature as the outside air-and there it freezes, creating the ridge or dam. Eventually the runoff water can back up under the shingles or through cracks in the roof.
As water starts to penetrate the sheathing, insulation, wall cavities, and sheetrock or plaster, several things can happen.
- Roof coverings, fascia, and gutters can be damaged
- Paint can start to peel on both the inside and outside walls
- Structural damage can result from the weight of an ice dam
Roof systems are not designed to channel water from the high points of the roof to the lower sections, where it should then exit the roof either through the gutter system or onto the ground.
Prevent Ice Dams
The damage caused by ice dams can be controlled in 2 ways: Maintain the entire roof surface at ambient outdoor temperatures or build a roof so that it can’t leak into sensitive building materials if an ice dam forms. Proper insulation and roof ventilation can stop ice dams from forming, prevent damage and lower energy bills.
Insulation: Houses in the northern United States should be equipped with ceiling insulation of at least R-38 (about 12 inches of fiberglass or cellulose). The insulation should be continuous and consistently deep. The most notable problem area is located above the exterior wall. Raised-heel trusses or roof-framing details that allow for R-38 above the exterior wall should be used in new construction. In existing structures, where the space between the wall’s top plate and underside of the roof sheathing is restricted, install high R/inch insulating foam (R-6/inch). Be sure to seal the insulation at this point to prevent warm-air leakage from the living space.
Ventilation: A soffit-to-ridge ventilation system is the most effective ventilation scheme you can use to cool roof sheathing. Power vents, turbines, roof vents and gable louvers just aren’t as good. Soffit and ridge vents should run continuously along the length of the house. A baffled ridge vent (like the one sold by Air Vent) is best because it will exhaust attic air regardless of wind direction. The exhaust pressure created by the ridge vent sucks cold make-up air into the attic through the soffit vents. A 2-inch space or “air-chute” should be provided between the top of the insulation and the underside of the roof sheathing in all applications. The in-coming “soffit” air washes the underside of the roof sheathing with a continuous flow of cold air.
CAUTION: Be sure to install insulation baffles above the exterior wall to protect the insulation from the air that blows in through the soffit vents.
Air Leakage: Insulation retards conductive heat loss, but a special effort must be made to block the flow of warm indoor air (convection) into the attic or roof area. Small holes allow significant volumes of warm indoor air to pass into attic spaces. In new construction avoid making penetrations through the ceiling whenever possible. But when you can’t avoid making penetrations or when you need to air-tighten existing homes use urethane spray-foam (in a can), caulking, packed cellulose, or weatherstripping to seal all ceiling leaks like:
- wire penetrations
- plumbing penetrations
- ceiling light fixtures
- attic hatches
- chimneys
- bathroom exhaust fans
- intersection of interior partitions and ceiling
So the message here is to check your home carefully when ice dams form. Investigate even when there doesn’t appear to be a leak. Look at the underside of the roof sheathing and roof trim to make sure they haven’t gotten wet. Check the insulation for dampness. And when leaks inside your home develop, be prepared. Water penetration often follows pathways difficult follow. Don’t just patch the roof leak. Make sure that the roof sheathing hasn’t rotted or that other less obvious problems in your ceiling or walls haven’t developed. And then detail a comprehensive plan to fix the damage. But more significantly, solve the problem.
Some people suggest a snow rake to remove the rooftop snow and slow down the ice dam growth. Others suggest using a hose to cut channels through the ice dam. But we don’t recommend people getting up on ladders in the winter to rake off or hose down the roof. And besides, both would only be temporary solutions.
Get advice from a professional roofing contractor for free roof inspection who can do an evaluation to isolate the problem. You’ll not only find out where the problem is on your roof but you’ll also probably learn if other parts of your home are leaking hot air as well.
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