Short version: replacing shingles is usually fine. Touching what is under them usually is not.
The long version matters because this service area covers twelve municipalities across six counties, and permit rules are set by each of them rather than by the province. There is no single southwestern Ontario answer, and anyone who gives you one has not checked.
The line that actually matters
It is not the size of the job or the cost of it. It is whether you are working on the surface or on the assembly.
| Work | Typically |
|---|---|
| Like for like asphalt shingles on sound sheathing | No permit |
| Spot repair of a small area of deck | No permit |
| Replacing sheathing beyond minor repairs | Permit |
| Changing roofing material | Permit |
| Modifying rafters or trusses | Permit |
| Raising a roofline, adding a dormer | Permit |
| Cutting in a skylight that needs new framing | Permit |
One verified example from this corridor
Sarnia publishes its exemption list, and “replacing stucco, siding, or shingles with the same material” sits on it. Structural work does not — foundation and structural repairs are named on the permit-required side.
That is one municipality of twelve, quoted because it is written down rather than because it settles the question for Stratford, Woodstock or Chatham. Ask yours. It is one phone call and it takes less time than reading this page.
Do I need a permit to change from shingles to metal?
Generally yes, and treat that as the default rather than the exception. A material change alters the assembly and its dead load, and most building departments want to see it. That is true in both halves of this corridor, though for different reasons — snow load in the snowbelt around Listowel and Goderich, uplift on the exposed flat farmland down towards Leamington.
Exempt is not unregulated
This is the misunderstanding that produces the worst roofs in the region.
A permit exemption is a statement about municipal process. It says the building department does not need to review this job. It says nothing whatsoever about what the job has to be.
The Ontario Building Code still applies. In the article governing installation of roofing materials it requires them to be installed in conformance with the manufacturer’s written instructions — which makes the shingle wrapper and the application sheet enforceable documents rather than suggestions.
What that quietly pulls in
Manufacturer instructions are where the specification actually lives. They set the nailing pattern and the number of fasteners, the starter course, the underlayment, the treatment of valleys, and the conditions under which the product may go over an existing roof at all.
So “no permit needed” and “nobody will check” are two different statements, and the second one is only true until there is a claim, a sale or a leak.
Where the eave protection question comes in
Ice-and-water membrane at the eaves is not a preference in the snowbelt half of this service area, and how far up from the eave it runs is the single largest specification decision on a snowbelt roof.
A permit will not tell you to get that right. The code, the manufacturer and the snowfall figure for your town will. Stratford sits at roughly 218 cm a year and Chatham at about 79 cm, and a specification written for the second and used on the first is quietly under-built. Nobody finds out for years.
The paperwork that actually protects you
Three documents matter more than the permit does on an ordinary re-roof.
The written scope. What is coming off, what is going on, how many nails per shingle, how far the membrane runs, and what happens if the deck turns out to be soft. A deck allowance agreed in advance is the difference between a change order and an argument.
The photographs. Of the deck, once the tear-off exposes it. That is the only moment anyone can see the one part of your roof that decides whether the rest was worth doing, and going over the old shingles removes that moment entirely.
The written findings. Ask for them from whoever quotes you, and take them elsewhere if you want a second price.
What we will tell you not to spend money on
A permit you do not need, on a like for like re-shingle, because somebody told you every roof needs one.
A material change you have not priced properly. The permit is the small number in that decision. The framing review, the assembly change and the disposal are the large ones, and they belong in the cost conversation before the aesthetic one.
And do not let anybody skip the deck inspection because the job is exempt. The exemption is about paperwork. The deck is about whether your new roof replacement is sitting on something sound.