Ice Dams in Winnipeg: Why They Form and How Eavestroughs Help Prevent Them

Winnipeg winters are exactly the conditions ice dams need: real snow load, and enough deep-freeze stretches to keep them building for weeks. If you've noticed a thick ridge of ice along your roof edge, or icicles heavy enough to worry about, it's worth understanding what's actually happening before it causes damage inside the house.

How an ice dam actually forms

It comes down to three things happening at once:

1. Heat escapes through the roof. Warm air from inside the house leaks into the attic and warms the underside of the roof deck.
2. Snow melts unevenly. The warmer upper roof melts snow, which runs down toward the colder eaves — the part of the roof that overhangs unheated space and stays near outdoor temperature.
3. It refreezes at the edge. That meltwater hits the cold eave and freezes solid, building a ridge of ice. Water behind the dam has nowhere to go but back up, under the shingles, and eventually into your attic or walls.

What role does the eavestrough play?

Your eavestrough isn't the root cause of an ice dam — that's almost always attic heat loss — but it matters in two ways:

• A clogged or undersized eavestrough freezes faster. Standing water and debris in the trough gives ice more to build on, and blocks the path water would otherwise take to drain away before freezing.
• Damage often shows up there first. The weight of built-up ice is what pulls hangers loose, cracks seams, and bends sections — even if the underlying cause is upstairs in the attic.

What to do if you already have one

Don't try to chip ice off the roof yourself — it's a good way to damage shingles or fall. A few safer steps:

• Use a roof rake from the ground to remove excess snow load before it can melt and refreeze
• Keep an eye out for water stains on interior ceilings near exterior walls — an early sign water has gotten past the dam
• Get eavestrough and attic ventilation assessed together once you're able to, so next winter doesn't repeat this one

If water is actively coming into the house, that's not a wait-for-spring problem — see our ice dam & storm response page for priority scheduling.

The good news: a well-sized, well-sloped eavestrough paired with decent attic ventilation makes ice dams far less likely, even in a Winnipeg winter. It's a lot cheaper to sort that out in the fall than to deal with water damage in February.