Before winter in the GTA: eavestroughs, downspouts and ice dams (2026)

Trade Talk Roofing
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From LF Builders, the renovation company behind this forum. Code and City guidance checked on October 30, 2026. Corrections welcome; reply below.

Short answer: Clear your eavestroughs and downspouts after the leaves are down and before the first hard freeze. Make sure every downspout drains away from the house, about 2 m from the foundation, without running across a walkway. Ice dams form when heat from the house melts snow on the upper roof and the meltwater refreezes at the cold eaves. That’s why the Ontario Building Code requires eave protection under shingles across the GTA: at least 900 mm up from the roof edge, and reaching at least 300 mm inside the inner face of the exterior wall.

Eavestroughs and downspouts

The City of Toronto’s advice, in its own terms:

  • Clean eavestroughs at least twice a year, and clear leaves, snow and ice from eavestroughs and downspouts.
  • Drain away from the foundation, ideally about 2 m out.
  • Plan for freezing. Water from a downspout can freeze in winter. Don’t run extensions across walkways, and take rain barrels out of service for the winter.
  • Keep it on your property. Disconnected downspouts must not send water onto a neighbour’s property, a sidewalk or a driveway.

A cleaning once the trees near your house are bare catches the leaves that fall late. When you’re up there, check the slope toward each downspout, the seams and end caps, and whether the downspout outlet is clear. See also When should I clean my eavestroughs in Toronto before winter?

Why ice dams happen

Snow on the roof melts where the roof deck is warm, over the heated house, and the water runs down to the overhang. The overhang sits outside the heated space, so the water refreezes there. The ridge of ice grows, water pools behind it and works back under the shingles. Clogged eavestroughs make it worse, but the root cause is heat getting into the roof space: air leaks from the house and not enough insulation, plus poor ventilation.

That’s why the fixes that last are air sealing and insulation at the ceiling below the attic, plus working ventilation. Heat cable and gutter guards treat symptoms. Two older threads dig into the guard question: Can gutter guards cause ice dams? and Is there a downside to gutter guards?

What the code requires: eave protection

The 2024 Ontario Building Code, Article 9.26.5.1, requires eave protection on shingle, shake and tile roofs. That’s a waterproof membrane at the bottom of the roof, under the shingles, that keeps water backed up behind ice out of the house. It must:

  • extend at least 900 mm up-slope from the edge of the roof, and
  • reach at least 300 mm inside the inner face of the exterior wall.

There are exceptions: over unheated garages, carports and porches; where the overhang is more than 900 mm; on low-slope shingle roofs built to their own rules; on very steep slopes (1 in 1.5 or steeper); and in regions with 3,500 or fewer heating degree-days. That last exemption doesn’t apply in the GTA. The code’s climate table puts Toronto City Hall at 3,520 degree-days, North York at 3,760 and Vaughan (Woodbridge) at 4,100.

If you’re getting a roof quote, ask the roofer to write the eave protection into it: how far up the roof it runs, and how it relates to your wall line.

A short fall checklist

  • [ ] Eavestroughs cleared, and water runs to each downspout
  • [ ] Downspouts drain about 2 m from the foundation, not across a walkway or onto a neighbour’s lot
  • [ ] Rain barrels drained and disconnected for winter
  • [ ] Attic looked at from the hatch: frost on nail tips or damp insulation can mean warm, moist air is getting in
  • [ ] Any roof quote names its eave protection

If you’d rather have it done: LF Builders runs a public eavestrough page here. It’s our own company, so weigh it with that in mind, and compare quotes using what a complete eavestrough quote includes.

Tell us what worked

  • Ice dams last winter: what actually fixed it? Air sealing, insulation, venting or heat cable?
  • What did a fall eavestrough cleaning cost you this year, and where in the GTA are you?

Sources

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