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An Ice Dam is a hump of ice that forms at the edge of a roof under certain wintertime conditions. An ice dam can damage both your roof, gutters, downspouts and the inside of your home.
They are common sights during our Manitoba winters. You can do several things to avoid ice dams or to reduce the risk of damage after one has formed, but there’s really only one cure and that is a combination of better sealing, insulation, and venting in the attic and eaves.
HOW ICE DAMS FORM?
These form whenever the roof over the attic is warm enough to begin melting the bottom of the layer of snow on the roof. The water travels between the layer of snow and roof surface until it reaches the eave which stays cold because it extends beyond the side of the house. There, it refreezes, gradually growing a mound of ice.
The flatter the pitch of the roof, the easier it is for an ice dam to get a grip. If snow and ice become high enough in the gutter, it can provide a foundation for an ice dam.
WHAT DAMAGE ICE DAMS CAUSE?
A large enough ice dam can let water drip onto attic insulation and even down into the ceilings and exterior walls beneath the eave, ruining the home's interior. If it breaks free, it can pull shingles and gutters with it, and will damage anything it falls on. Ice weighs nearly 55 pounds per cubic foot. Consider that just 2 inches by 4 inches of ice spread along the edge of a 35 foot roof would weigh 107 pounds. If the roof sheathing stays wet, mildew and rot can also start.
DEALING WITH EXISTING ICE DAMS
1. Remove the ice dam by breaking it free in small chucks. Do NOT use sharp tools! You’ll cut through the shingles. Instead, tap lightly with a blunt mallet. The chunks of ice can take pieces of shingle with them.
2. Clear out gutters and downspouts. This can damage either plastic or metal gutters and spouts.
This is all dangerous work, so please hire someone experienced at roofing.
3. Melt troughs through the dam with calcium chloride ice melter.
NO rock salt! It will damage paint, metals, and plants wherever the salty water drains.
A good trough-maker is a tube of cloth (a pair of panty hose works well). Fill it with ice melt, tie off the top, and lay it vertically across the ice dam. It slowly melts its way through the dam, clearing a path for the underlying water to flow free.
4.You can scrape snow from the roof whenever it falls, using a snow rake, broom or plastic shovel. BE CAREFUL: The first item can bury you in snow, while the second and third can send you slipping off the roof. Hire someone who knows how to use a safety line.
5.You can replace your shingle roof with standing seam or other metal roof. You can replace the bottom three feet with a wide metal drip edge. Whatever you do, install a water-repellant membrane under any new roofing.
NOTE: If your roof is not very steep, an ice dam can still form on metal roofing and drip edges.
These treat the symptoms, not the problem, that is the warm roof, caused by poor insulation and venting of the space under the roof.
THE BEST CURE
There is only one way below to cure an ice dam and prevent one in the first place that is to:
1. Seal all points where warm air leaks from the living space into the spaces immediately below the roof sheathing.
2. Insulate the living space enough to prevent heat conduction and convection through the ceiling.
3. Vent the space between the insulation and the roof sheathing, so any heat leakage is carried away.
These will also cure a significant loss of heat from your home. It’s a win-win situation: You save on fuel bills which can pay for the work to protect yourself from ice dams, and your tighter home will feel more comfortable during these long cold Manitoba winters.
George Adair, Certified Professional Home Inspector
I provide a wide range of home inspection and home inspection related services in the following areas of southern Manitoba: Winnipeg, Selkirk , Lockport,Steinbach,
Stony Mountain, Elie, Rosser, Lorette Sanford, East St. Paul, West St. Paul, Oak Bank,
Oak Bluff, Landmark,
St. Anne, Saint Andrews,
La Salle, Richer, Niverville and Warren.
Our extended area also includes: Lac Du Bonnet, Beausejour, Libeau, Gimli, Pinawa, Falcon Beach, Winnipeg Beach, Grand Marais, Saint Laurent, and Pine Falls