The last few winters have put a foot of ice on roofs out here
The pattern goes like this. A heavy snowfall lands. Then a warm spell — Ontario can reach ten degrees in January — and it melts down and turns ice-like. Sometimes wet snow or outright rain adds to it. Then the temperature drops hard overnight and it flash freezes. Repeat that a few times and the layer builds. Customers have reported a foot of ice sitting on the roof, and it does not leave quickly: in spring it can take three weeks to melt off. That whole time it is dead weight and constant pressure, with no airflow underneath. On shingles that are already curled, cracked, or shedding their granules, meltwater finds a way through — into the plywood deck, and then into the attic or the room below it. We were called to a roof in Angus where exactly that happened — meltwater came through and into an upstairs bedroom. On another job, the owners had gone away for the winter and came home to find the kitchen ceiling had come down, taking most of the room with it. Both became insurance claims. Whether ice damming is genuinely getting worse or the last few winters have simply been bad ones, we cannot say. It has been noticeably more common.