The local factors behind downspout extensions & drainage in Markham
Two houses on the same Markham street, built the same year, can need completely different downspout extensions & drainage work — and usually do.
Range hoods and basement bathroom fans routinely out-pull an older flue, so the house depressurises and the flue reverses — a Markham problem that looks like a chimney fault but starts elsewhere in the building.
Snow load and ice damming stress the roof-to-wall junction each winter; by spring the sealant that was doing the work has usually torn.
Across Cornell, Rouge River, Markham Village, Raymerville and Commerce Valley, 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 downspout extensions & drainage 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.