The difference between a $200 service call and a $6,000 rebuild in Markham is usually about eighteen months of ignoring a small symptom.
Wind loading off Lake Ontario pushes driving rain against the south and west faces of a house, which is why water entry so often shows up on one side of a Markham home and nowhere else.
Older Markham stock was built when soft lime mortar and clay liners were the standard; modern high-efficiency appliances vent very differently, and the mismatch causes condensation the original builder never planned for.
Across Victoria Square, Bayview Glen, Rouge River, Markham Village and Royal Orchard, 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 Main Street Unionville, the practical takeaway is that a winter roof prep 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.