Snow On The Roof
Most Toronto roofs handle a normal winter without help. The cases that need attention are specific, and the damage from clearing badly is common.
Short answer
A sound roof built to the Ontario code carries the design snow load for the area. The situations that warrant clearing are drifted or sliding snow piling deep on one area, a flat or low-slope roof holding water and slush, a rain-on-snow event adding weight, and any roof already showing signs of distress.
When it matters
Drifting, which piles snow far deeper on one part of a roof than the general depth suggests — typically behind a parapet, against a dormer or in a valley.
Sliding from an upper roof onto a lower one, which concentrates the load from two surfaces onto one.
Flat and low-slope roofs, where meltwater and slush sit rather than running off, and where a blocked drain turns snow into standing water.
Rain on snow, which is the genuinely dangerous Toronto event — the snowpack absorbs the rain and the weight climbs sharply within hours.
A roof with existing structural issues, a previous modification, or a known deflection.
And porches, carports, sunrooms and additions, which are frequently framed lighter than the main roof.
Signs of distress
A visibly sagging roof line, doors or windows that suddenly stick, new cracks in drywall at the ceiling or above openings, creaking or popping, and a sprinkler line or light fixture that has moved. Any of those with snow on the roof is a reason to get off the floor below and call somebody today.
The damage from clearing badly
Shingles torn and granules stripped by a metal shovel or a scraper.
A roof rake dragged up the slope, which lifts the shingle courses.
Flashing and vent boots damaged under snow where nobody can see them.
Eavestrough pulled off by snow and ice dropped on it from above.
A membrane roof punctured, which is a leak that appears in spring.
And the obvious one: a fall from a ladder or a roof in winter, which is how most people are actually hurt by this.
Doing it properly
From the ground where possible, with a roof rake used to pull snow down the slope rather than up it.
Leave a layer rather than scraping to the shingle, which protects the roof surface.
Clear the eave and the valley area first, which is where the ice dam will otherwise form.
Clear flat roof drains and scuppers, which is frequently the whole job on a commercial roof.
Keep clear of the drop zone, and keep eavestrough and vents in mind.
And address the heat loss over the summer, because an attic that is properly sealed and vented keeps the snow where it belongs.
Common questions
Do I need to clear snow off my roof?
Usually not. Drifting, sliding onto a lower roof, a flat roof, or rain on snow are the cases that matter.
What is the most dangerous event?
Rain on snow. The pack absorbs it and the weight climbs within hours.
Can I use a shovel on the shingles?
No. Use a rake from the ground, pull down the slope, and leave a layer.