What makes ice dam risk in Vaughan unusual is not the technique, it is the age spread of the housing: a single route can cover 1910 brick and 2019 factory-built venting.
Air-sealing and window upgrades have made Vaughan homes far tighter than they were designed to be, and a tight house starves a natural-draft appliance of the make-up air it needs.
Range hoods and basement bathroom fans routinely out-pull an older flue, so the house depressurises and the flue reverses — a Vaughan problem that looks like a chimney fault but starts elsewhere in the building.
Across Rainbow Creek, Pine Grove, Kleinburg, Thornhill Vaughan and Uplands, the housing stock changes street by street, and the correct method changes with it. A century home with a soft-brick stack does not get the same treatment as a 2010 build with a factory-built vent — using one method on both is how systems get damaged.
If you live anywhere near Vaughan Metropolitan Centre, the practical takeaway is that a ice dam risk visit should start with an assessment, not a tool. Any crew that begins work before telling you what they found is guessing on your behalf.