This winter has brought exceptionally rare conditions for ice dam formation in Southern Ontario, particularly in the Waterloo Region. With weeks of sustained below-freezing temperatures and multiple snowfalls, we are seeing the perfect storm for ice dams to develop. Typically, our winter climate includes periodic warm spells that help melt any forming ice dams before they become problematic. However, the persistent cold has allowed ice dams to grow large enough to trap water, leading to potential leaks through the roof.
How Ice Dams Form
Ice dams occur when heat from inside the home causes the roof to warm up, melting the snow sitting above. As the melted water runs down to the colder eaves, it refreezes, gradually building up into a ridge of ice. The eaves remain colder than the rest of the roof because they overhang the house walls, meaning there is no heat rising from below to warm them up. This ridge of ice traps additional melting snow, preventing proper drainage and causing water to back up under the shingles.
Shingles are not a waterproof membrane—they are designed to overlap and shed water, but they cannot prevent leaks if water becomes trapped in a puddle on the roof. To help protect against leaks caused by ice dams, most roofs have an additional layer under the lower edge of the shingles known as eave protection (commonly called Ice-Water Shield). This acts as a backup barrier to reduce the risk of water penetration. However, on lower-sloped roofs, additional coverage may be necessary to provide proper protection against ice dam-related leaks. Additionally, some roofs may not have eave protection properly installed, or it may not have been installed at all, increasing the risk of leaks.
Eventually, if ice dams persist and grow, trapped water can find its way inside the home, leading to costly damage. Eavestroughs can be severely bent or even pulled right off of the building.
How to Prevent Ice Dams
Preventing ice dams is primarily about managing heat loss and ensuring proper ventilation. Here are some effective strategies:
Improve Attic Insulation: A well-insulated attic keeps warm air from escaping, reducing uneven roof temperatures that lead to ice dam formation.
Enhance Ventilation: Proper soffit and ridge venting helps maintain a uniform roof temperature by allowing cold air to circulate through the attic space.
Seal Air Leaks: Gaps around light fixtures, plumbing vents, and attic hatches allow warm air to escape, contributing to uneven roof melting.
Use a Roof Rake: After heavy snowfall, safely removing snow from the lower sections of your roof can help prevent ice buildup.
Consider Heated Cables: In some cases it is not practical nor possible to change a roofline's geometry. Installing heated cables along the eaves and in vulnerable areas can help prevent ice accumulation.
Houses Most Vulnerable to Ice Dams
While any home can experience ice dams under the right conditions, certain houses are particularly susceptible:
Poorly Insulated Homes: Some homes, even newer homes, may have areas where insulation has settled or collapsed, allowing unnecessary heat to escape.
Half-Storey Homes: These houses lack a full attic above the upper floor, leading to significant heat loss through sloped ceilings.
Homes with Cathedral Ceilings: Without an attic buffer, cathedral ceilings allow heat to rise directly to the roof surface, making ice dam formation more likely.
Dormer Features and Roof Valleys: Dormers create valleys and complicated rooflines where snow can accumulate and ice dams can easily form. Converging valleys and restricted areas where snow builds up can also be problem spots.
Improperly Vented Exhaust Fans and Ducts: Some homes have exhaust fans that don’t vent properly outside, allowing warm, moist air to escape into the attic. Additionally, exhaust ducts running through the attic—even when insulated—can cause localized heat buildup, increasing the risk of ice dam formation.
With this winter’s unique weather conditions, homeowners in the Waterloo Region should be extra vigilant in monitoring their roofs for signs of ice dam formation. Taking proactive measures can help prevent costly damage and keep your home safe and dry throughout the season.
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