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Roof Repair in Ontario: Finding Leaks, Repair Costs, Ice Dams, Ventilation and the Attic Problems That Look Like Roof Problems
RoofingRepairs & Leaks
Roof Repair in Ontario: Leaks, Ice Dams, Flashing, Ventilation, and the Half of It That Is Not the Roof
How to find where the water is really coming in, what each repair costs, and the attic problems that get sold as new roofs.
I get called about roof leaks that are not roof leaks about as often as ones that are. Frost in the attic melting in March, a bathroom fan dumping steam onto cold plywood, an ice dam backing water up under shingles that are in perfect shape. The roofer who shows up wants to sell a roof, because that is what the roofer sells. These pages are the fifteen minutes of looking that tells you what you are actually dealing with, and what the honest fix costs.
The numbers
Ontario, October 2026, a reputable roofer, before HST. Most roofers carry a minimum call-out of $350 to $500 that the first hour of any of these sits inside.
$350 – $500minimum service call
$650 – $1,200chimney re-flash
$900 – $2,000valley rebuild, one side
$350bathroom fan ducted out properly, with a roof
The guides
How to find a roof leak
Where the water comes in is never where it shows up. How to trace it from the attic, in order.
Roof repair cost in Ontario
Every common repair priced, and the three where the cheap fix is the expensive one.
Ice dams
Why they form, why the roofer cannot fix them, and the three things that do.
Attic ventilation
The 1-in-300 rule, soffit and ridge done right, and the mistakes that cook a roof from underneath.
Chimney and wall flashing leaks
What proper flashing looks like, why caulk is not flashing, and the cricket nobody installed.
Valley leaks
Open metal, closed-cut and woven valleys, why yours leaks, and what a rebuild costs.
The bathroom fan venting into the attic
The most common cause of attic frost and mould in Ontario, and the $350 fix.
Leak or condensation?
The stain that only appears in a thaw, and how to tell which one you have before you call anybody.
Read these in this order
- Is it a leak at all? If the stain shows up in a thaw and dries by spring, start with leak or condensation. If it shows up during rain, find the leak.
- Where does it come in? Chimneys, walls and valleys account for most real leaks on roofs under 15 years old. Flashing, not shingles. Flashing and valleys.
- What is it going to cost? Every repair priced, including the three where patching is more expensive than fixing.
- Is the attic making it worse? Ice dams and frost come from heat and moisture getting into the attic, not from the roof. Ventilation, ice dams and the bathroom fan.
- Is it worth repairing? On a roof over 18 years with more than one problem, usually not. Repair or replace.
Related on this site
- Attic insulation R-value in Ontario: the insulation half of the ice dam problem.
- Attic insulation cost: what topping it up costs, and when to do it.
- Truss uplift: the winter ceiling crack that is neither a leak nor condensation.
Have a quote in hand? Let a builder read it first
For $99, I read your roofing quotes and your roof photos and send back a written note: what is missing from the scope, where the price is out of line with October 2026 Ontario rates, what to ask the roofer before you sign, and whether the roof should come off at all this year. Two business days. How the roofing quote review works.
