It looks like a roofing failure. It is almost never caused by the roof.
Here is what is actually happening up there. Heat gets into your attic and warms the underside of the deck. Snow sitting on that part of the roof melts, the water runs down to the overhang — which hangs past the heated part of the house and is therefore cold — and refreezes. A ridge of ice builds at the eave, and the next lot of meltwater has nowhere to go, so it pools behind the ice and works backwards under a shingle lap.
Shingles shed water running downhill. Against standing water being pushed uphill they do precisely nothing.
So it comes in, runs along a rafter, and turns up as a brown ring on a bedroom ceiling. The roof did not fail. The attic did.
Which half of this corridor this applies to
A dam needs snow to sit on a roof for weeks, not days. Which is why this is a very local problem.
Stratford averages about 218 cm a year, Listowel about 192, Strathroy about 170, and the country inland of Goderich more again — snow squall warnings for that stretch are a routine part of an Ontario winter.
Chatham averages 79 cm and Leamington 86. Snow rarely stays long enough there for a dam to build, which genuinely removes the failure mode.
The same house with the same insulation behaves completely differently at the two ends of this corridor. Which is why national advice on ice dams is useless in half of it, and why a roofer who cannot tell you what your town actually gets is guessing at your specification.
Where the heat is getting in
Four culprits account for most of it. Not one of them is on the roof.
Recessed light fixtures. Older ones are effectively holes in the ceiling with a warm appliance in them. They vent heated air straight into the attic.
A bathroom fan ducted into the attic. Common, and worse than no fan at all: it delivers warm, wet air directly onto the underside of the deck, which produces both a melt and a frost problem.
The attic hatch. Frequently a sheet of plywood with no weatherstrip and no insulation on top, sitting in the ceiling of a heated hallway.
Insulation pushed into the soffits. Usually done by somebody topping up the attic, and it blocks the intake at exactly the point where the ventilation path needs to start. The attic then cannot flush the heat that does get in.
Ventilation is the second half
Air sealing stops heat entering. Ventilation removes what still does, and it only works as a path: intake low at the soffit, exhaust high at the ridge, with a clear run between them.
A ridge vent with blocked soffits is not ventilation. It is a hole at the top of a sealed box.
Removal, and what not to let anyone do
If someone turns up at your house in February with a hammer, a chisel or a pressure washer, send them away.
Steam is the correct method. Slower, more expensive on the day, and the only approach that takes the ice off without taking granules, shingles and quite often the eavestrough along with it.
Chipping causes damage that does not surface until April — by which point nobody connects the new leak to the person who was paid to stop one.
Salt pucks in a stocking and heat cable both manage a symptom. Heat cable has a legitimate place on a geometry that genuinely cannot be ventilated — a valley over a cathedral ceiling, a dormer cheek with no attic behind it — and it runs up an electricity bill every winter it is used. Neither finds the heat leak.
What this costs, and in what order
Steam removal of an active dam runs from a few hundred dollars to a few thousand depending on how much ice there is and how much of the roof it covers. That is the emergency.
The fix is separate and it is cheaper: air sealing the attic penetrations, correcting a fan duct, adding baffles so the soffits can draw. It is unglamorous work in a cold attic and it is the only spend that stops the problem recurring.
You can do the fix on its own in summer, and honestly that is the right time. A house that dammed last winter will dam again next winter unless something changed in between — and August is a considerably nicer month to be crawling round an attic than January is.
What we will tell you not to spend money on
A new roof, if the roof is otherwise sound. Replacing shingles does not change the temperature of the deck. Extending ice-and-water membrane further up from the eave is genuinely worth doing when the roof is being replaced anyway, in the snowbelt half of this corridor especially — but it is a second line of defence, not a fix.
Heat cable as a first resort, on a roof that could be ventilated properly for less.
Ripping out insulation. More often the problem is that insulation is in the wrong place — in the soffits — rather than that there is too much of it.
Related reading: what a roof replacement costs here, and the ice dam service page.