Ice dams, attic ventilation and the winter damage nobody budgets for

Ice dams are an attic problem wearing a roof costume

Every winter southern Ontario homeowners call roofers about ice dams, and a good number of them do not need a roofer. The mechanism is heat: if your attic sits above freezing, it warms the roof sheathing, snow on the field of the roof melts, the water runs down to the overhang where there is no heated space beneath it, and refreezes into a dam. Water then backs up behind that dam and finds its way under the shingles.

So the durable fixes are air sealing, insulation and ventilation, not bigger eavestroughs.

"If your roof is bald in patches after a snowfall and your neighbours' roofs are still white, that is not good luck. That is your heating bill going through the ceiling, and the ice at the eaves is the receipt."

Mitch Fraser, owner, Ontario Contracting Co.

What the Building Code actually requires

• Attic ventilation: unobstructed vent area of not less than 1/300 of the insulated ceiling area, increasing to 1/150 where the roof slope is less than 1 in 6 or for roofs built with joists.
• Eave protection: required on shingle roofs, extending at least 900 mm up the slope to a line not less than 300 mm inside the inner face of the exterior wall. There is an exemption for regions with 3,500 or fewer heating degree-days, and this is the local point that matters: Brantford and Hamilton are both well above that threshold, so the exemption does not apply here.
• Exhaust ducts: exhaust systems must discharge directly outdoors, not into an attic or other enclosed space, and ducts passing through unheated space need provision for condensation.

That last one is the single most common defect we find during winter callbacks: a bathroom fan blowing warm, wet air straight into the attic, frosting the sheathing, then dripping in the January thaw and getting blamed on the roof.

Do you have to upgrade insulation to current standards?

Not in an existing house. The R-values circulating online come from SB-12, which sets energy-efficiency requirements for new construction and major renovations, and it is package-based rather than a single blanket number. If someone quotes you a specific R-value as a legal obligation for a retrofit, ask which table they are reading. Upgrading is usually worth doing on its own merits (that service, sequenced air-seal-first, is our insulation practice), especially with provincial insulation rebates paying up to $7,700, but it is a choice rather than an order.

Spring, and the other half of the problem

The same water that dams at your eaves in February arrives at your foundation in April. Grading, downspout discharge distance and weeping tile are the ground-level version of the same story, and in Brantford the City will pay 80 percent of prevention work to $5,000 while Hamilton runs the S3P grant. Foundation depth matters too: the Code prescribes a minimum 1.2 metre foundation depth in clay for heated basements, and requires unheated foundations to bear below the frost line, which is why an unheated addition or deck footing done shallow heaves and cracks by its second winter.