Take steps to avoid ice dams and leaks

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While some people welcome our Canadian winter as a wonderland, many dread the effort needed to maintain your car and home and to stay warm and safe. If you haven’t already had the joyful experience an ice dam, then take a few minutes now to learn how to avoid one. It is not an item for anyone’s bucket list.

Have you ever driven by a house where the snow seems to be in panels every 16” or so? This is a clear indication of heat loss into the attic as it melts the snow between the trusses or rafters. If that house, is your house, then you should take special note of the info below. To explain, ice dams are large masses of ice that collect in gutters or on the lower edge of a roof. They usually occur when a significant depth of snow accumulates on the roof. If the attic temperature is above freezing, it warms the roof sheathing, which melts the snow lying on the shingles under the snow. This water runs down the roof to the overhang, which is not warmed by the attic. The water freezes on the roof starting the ice dam. As more melting snow (or rain) runs down the roof, it meets the ice and backs up, sometimes under the shingles and into the attic or the house. Most people don’t realize this is happening until drywall, carpet or furniture are damaged.

What to do? First, inspect the attic to determine the point of penetration. Attics can be tricky to navigate and evidence of water may not be obvious. Water can run along the attic floor a distance before coming through the ceiling, making it very difficult to determine it’s entry point.

Obvious areas such as chimneys, plumbing vents, and attic vents – anything that penetrates the roof sheathing – should be inspected first. If the sheathing (either boards, plywood, or composite board) along the lower edge of the roof is soaked and you can see a corresponding accumulation of ice on top of the roof, ice damming is occurring. This means that water is backing up under the shingles. Shingles are designed only to shed water running down, not up.

Your inspection may find that leakage is not the problem: the whole attic or part of it may be dripping with condensation or covered with frost.
Attic condensation and ice damming are related. Both can be caused by warm, moist air escaping from the house into the attic. You need good air sealing and insulation, to keep the attic cool and dry, and not cause snow to melt on the roof.

Increasing attic insulation is the most obvious fix. Fiberglass batt or blown-in insulation are easily added. Proper ventilation is also critical. Adequately sized vents on the roof and at the soffits with a clear unblocked airway between the two, will allow cool dry air to be drawn into the attic and warm moist air to be expelled.

One further step is needed, to reduce the amount of moist warm air leaking into the attic by ensuring:
- bathroom exhaust fans vent to the exterior and not into the attic
- potlights in the top ceiling are insulated sealed fixtures
- sealing around plumbing stacks, chimneys and electrical wires that pass through the attic floor
- sealing where partition or bearing walls meet the ceiling; around the house perimeter where the attic floor meets the outside walls
- insulating and sealing above pocket doors
- and have a professional ensure heating / air conditioning ducts or equipment in the attic are properly insulated and sealed.

A blower door test can locate less obvious air leaks by pressurizing the house with a big fan that amplifies leakage. Searching the attic at night for lights from below can also be helpful. Holes should be blocked and sealed.

For houses with complicated roofs or cathedral ceilings, electric heating cables, which will melt channels in the ice, can be considered.

Peder Madsen is the president of the London Home Builders' Association and Vice President of CCR Building and Remodeling in London.


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