Ice dams form when heat escaping through the roof melts snow, and that water refreezes at the colder eaves. Gutters packed with leaves trap the water and ice right at the edge, which helps the dam grow and pushes water back under the shingles. Cleaning your gutters in late fall, after the leaves drop, is the simplest way to reduce the risk before winter.
Long icicles along the eaves look pretty from the street. From inside the house they can mean something less charming: an ice dam, and water working its way under your shingles. In Northern Ontario, where snow sits on roofs for months, it pays to understand how ice dams form and what you can do before the first big snowfall.
What is an ice dam?
An ice dam is a ridge of ice that builds up along the lower edge of a roof. Behind it, melting snow pools on the shingles with nowhere to go. Shingles are designed to shed water running downhill, not to hold back a puddle, so that water can seep underneath and into the attic, the walls or the ceiling.
How do ice dams form?
It starts inside the house. Heat rises into the attic and warms the roof deck. Snow on the warm part of the roof melts, even on cold days, and the water runs down toward the eaves. The eaves hang out past the warm walls of the house, so they stay much colder. When the water reaches them, it freezes. Day after day, the ice ridge gets thicker.
Why clogged gutters make it worse
Gutters full of leaves, needles and grit hold water right at the edge of the roof. When that water freezes, the gutter becomes a solid block of ice — the perfect foundation for an ice dam to build on. Heavy ice can also bend gutters, pull out fasteners and tear sections away from the fascia.
A late-fall checklist
Clean the gutters after the leaves drop. In Greater Sudbury that usually means late October or November.
Check that every downspout flows. A blocked downspout turns a clean gutter into a trough of standing water.
Point downspouts away from the foundation. Spring melt should drain away from the house, not into the basement.
Look for sagging or loose sections. Gutters that pull away from the roof hold water and ice.
Have a look in the attic. Damp insulation, frost on nails or daylight around vents are signs of heat and moisture escaping.
Fixing the root cause
Clean gutters reduce the risk, but the real cause of ice dams is heat escaping into the attic. Good attic insulation, sealed gaps around lights, pipes and the attic hatch, and proper roof ventilation keep the roof deck cold so snow does not melt unevenly. An insulation or roofing professional can assess your attic if ice dams are a yearly problem.
What to do if you already have an ice dam
Stay off icy ladders and do not chip at the ice with a hammer or shovel — it is easy to damage shingles and gutters, and easier still to fall. Pulling snow off the lower part of the roof with a roof rake from the ground can relieve the pressure. If water is coming inside, or the ice is thick, call a professional for safe snow and ice removal.
Why spring matters just as much
Winter leaves its own mess behind. As the snow melts, gutters fill with shingle grit, twigs and seeds, and the spring melt is exactly when you need them flowing freely. A spring cleaning clears that debris before the rains start, and it is a good moment to spot gutters that sagged under the weight of ice or downspouts that came loose.
Walk around the house during the first good rain of the season. Water spilling over the front of a gutter, puddles forming next to the foundation or a downspout that stays dry are all easy signs that something needs attention. Catching those problems in spring means fewer surprises when the next winter arrives.
Where we can help
A late-fall gutter cleaning is one of the easiest ways to start winter on the right foot. We clear every run of gutter by hand, check that each downspout flows and let you know about anything loose or damaged we see along the way.
The bottom line
Ice dams come from heat, snow and cold eaves. You cannot control the snow, but clean, flowing gutters and a well-insulated attic take away most of the conditions they need to grow.
Frequently asked questions
When should gutters be cleaned in Sudbury?
At least twice a year: in spring, and in late fall once most leaves have dropped. Homes surrounded by trees may need an extra visit.
Do gutter guards stop ice dams?
Guards can keep leaves out, but they do not stop ice dams, which are caused by heat loss and snow. Guards still need occasional checking and cleaning.
Should I chip ice off my gutters?
No. Chipping or hammering at ice can damage shingles and gutters and is dangerous on a ladder. If an ice dam is causing a leak, call a professional.
What are the signs of an ice dam?
A thick ridge of ice along the eaves, large icicles, water stains on ceilings or exterior walls near the roofline, and damp insulation in the attic.
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