Repair the roof when the problem has one cause you can point to and the rest of the roof is sound. Replace it when the failures are spread out and unrelated, the wear is general rather than local, or the deck has been wet across a slope or along the eave, not just under one leak. Age only tips the balance. A roof in Stratford and a roof in Chatham can reach that line at different ages, and a roof that leaks once is not automatically a roof that is finished.
That is the whole rule. The hard part is knowing which side of it you are on, and that takes a few checks in a fixed order.
Start with the cause, not the stain
A water mark on a ceiling tells you that water got in. It does not tell you where, and it says nothing about the state of the rest of the roof. Before anyone talks about repair or replacement, somebody has to find the entry point. How to spot a roof leak walks through where water tends to run before it shows.
Once the entry point is known, the question gets much simpler. A split boot around a plumbing vent, a lifted piece of step flashing beside a dormer, or a nail that has backed out are each one cause with one fix. A leak like that on a roof with years left in it is a roof leak repair and nothing more.
If nobody can find a single cause, or the trace turns up three, that is your first real sign that the conversation is about the whole roof.
Then count the failures
One failure is a repair. Several unrelated failures at the same time are a pattern.
A 2026 repair guide from a contractor in Brantford lists four things that move the call towards replacement:
| Sign | What it tells you |
|---|---|
| The roof is 20+ years old | The shingles are near the end of their working life |
| More than 25 to 30% of the surface needs attention | Damage is spread out, so patches stop paying for themselves |
| Two or more repairs in the past five years | The materials are failing across the roof, not in one spot |
| Two layers of shingles already on | The next job is a tear-off whatever you do |
Read the table as a set. One line on its own is a reason to look harder. Two or three together are a roof that is telling you something.
Why the last line is not optional
A roof carrying two layers has nothing left to defer. The weight, the heat and the hidden deck are covered in the guide to roofing over existing shingles. For this decision the point is only that a second layer removes the cheaper choice.
Look at the deck from underneath
The deck is the plywood or plank layer the shingles are nailed to. Nobody can see its top surface without a tear-off, but you can see its underside from the attic hatch with a flashlight.
Look for dark staining on the sheathing, soft or swollen spots, rusty nail tips, and a white rime of frost on the sheathing in winter. Staining around one vent pipe points back to that pipe. Staining spread across a whole slope, or along the full length of the eave, is water that has been getting in for longer than one season. A stained patch under one vent or flashing gets cut out and resheeted as part of the repair, which is the small section of deck in the moderate row below. Staining across a slope or the full eave is a replacement.
Put the two prices side by side
The same Brantford guide gives these ranges for repair work:
| Repair | Published Ontario range |
|---|---|
| Minor: a few shingles, a single flashing seal | $350 to $800 |
| Moderate: flashing replacement, a valley, a small section of deck | $800 to $2,500 |
| Larger: a full valley, chimney reflashing, ice dam damage | $2,000 to $5,000 |
The same guide puts the replacement that tends to follow a repair on an aging roof at $8,000 to $18,000, and says that repairing one section of a roof that age often means another section fails within 2 to 3 years. What a full tear-off runs in this corridor, and what moves the number, is on the page for roof replacement cost in southwestern Ontario.
A minor repair on a sound roof is an easy yes. A larger repair at the top of its band is more than half the bottom of that replacement range. On a roof old enough that the next section fails inside those 2 to 3 years, the two repairs together come close to the price of starting again. That is the point to price both before you agree to either.
Where you are in the corridor changes the timing
This part is local. The snowbelt end of the service area and the Erie shore end wear a roof out in different ways, so the same age means different things.
How long does a roof last covers how snow and wind wear a roof differently by town. Here is what that means for the decision. If a twenty-year-old roof has started leaking at the eave every winter, in our judgement that is usually a membrane and deck problem along the full edge, which a patch at one spot does not reach. The cause is often heat in the attic, which is why an ice dam roof needs that fixed as well, whichever way you go on the shingles.
Tabs lost in a storm on one face of a sound roof are a repair. Tabs that keep lifting in ordinary wind, across several slopes, mean the sealing strips have let go, and the roof is closer to the end than it looks from the ground.
Four situations, and the call in each
One leak, a roof well short of twenty, one cause found. Repair, and keep the invoice.
A storm took shingles off one slope of a roof that was fine before. Repair, and talk to your insurer before you pay for it. What to photograph first for a roof storm damage insurance claim is set out separately.
A second or third leak in a year, from different places, on a roof near twenty. Get a replacement price before you approve the next repair, and see what a full replacement includes in the roof replacement scope. Each new repair is now buying less time.
You are selling. A buyer will ask how old the roof is and what has been done to it, so paperwork matters more than looks. A dated invoice for a repair answers that question. A fresh patch with no record raises it. If the roof is at the end, replacing it or adjusting the price are both honest answers. Hiding it is not one.
Get the call in writing
Ask whoever looks at your roof to put four things on paper: the cause of each problem they found, the condition of the deck as far as the attic shows it, a repair price for each item, and a replacement price for the whole roof. A roof inspection report with photographs gives you the same facts to take to a second roofer.
For the age question on its own, how long does a roof last explains what wears a shingle out along this corridor. If your roof is already at the end, roof replacement is the next page to read.