Every Ontario homeowner has seen icicles hanging from eaves in January. Most of the time, they're harmless. Sometimes they're a sign of a problem that's actively damaging your roof. Here's how to tell the difference.
How ice dams form
- Heat from your house rises into the attic
- The warm attic melts snow on the upper portion of your roof
- Meltwater runs down toward the eave
- The eave is cold (it overhangs the house, so there's no heat below it)
- The water refreezes at the eave, forming a ridge of ice
- More meltwater backs up behind the ice ridge
- The backed-up water has nowhere to go — except under your shingles
That last step is where damage happens. Water under shingles means water in your decking, insulation, walls, and ceilings.
When to worry
Small icicles along the eave? Usually fine. They're normal in an Ontario winter and don't necessarily mean you have an ice dam.
A thick ridge of ice along the eave edge? That's an ice dam forming. It's not emergency territory yet, but keep an eye on it.
Icicles plus water stains on interior ceilings near exterior walls? Active leak. The ice dam has backed water under your shingles and it's getting inside. Call us.
Large icicles hanging from the soffit or growing outward horizontally? This suggests significant ice buildup. It's heavy (ice weighs about 57 lbs per cubic foot) and can damage eavestroughs, fascia, and soffits.
What causes bad ice dams
The root cause is almost always heat loss from the attic. Common culprits:
- •Insufficient attic insulation (heat passes through the ceiling into the attic)
- •Bathroom exhaust fans venting into the attic instead of outside
- •Recessed lights in the ceiling below the attic that leak warm air
- •Inadequate soffit and ridge ventilation (warm air gets trapped)
What you can do
Short term (this winter): - If you see an active leak, call us for emergency service - Avoid hacking at ice with a hammer or axe — you'll damage the shingles - Calcium chloride ice melt in a stocking laid across the ice dam can create a drainage channel (don't use rock salt — it stains and corrodes)
Long term (before next winter): - Get your attic inspected for insulation and ventilation adequacy - Ensure ice-and-water shield extends at least 6 feet from the eave - Make sure bathroom and dryer vents exhaust through the roof, not into the attic - Consider adding soffit vents if airflow is poor
Ice dams are a solvable problem. The fix is usually attic-side (insulation and ventilation), not roof-side. A good roofer will tell you that.