Renovating a Century Home in Ontario: What's Really Behind the Walls

The usual suspects

Knob-and-tube wiring

Common in homes built before roughly 1950, and the single most consequential find: many insurers won't cover homes with active knob-and-tube, or will require its removal on a deadline. If a renovation opens the walls anyway, replacing it during the project is dramatically cheaper than as a standalone job later. Panels are the related find — a 60-amp service can't carry a modern kitchen, and upgrades need ESA-notified electrical work.

Plumbing from another era

Galvanized steel supply pipes corrode from the inside — weak pressure and rusty water are the symptoms — and some older homes still have lead service lines. Cast-iron drain stacks fail at the bottom first, where you can't see them. A bathroom renovation in a century home is often really a plumbing renovation with tile on top, and pricing it any other way is pretending.

Plaster, framing, and a hundred years of settling

Plaster-and-lath walls are repairable and worth keeping where they're sound — but they hide wiring routes, crumble around new openings, and take a different skill set than drywall. Rough-sawn framing is rarely square or level, floors dip toward the middle of the house, and none of that is alarming by itself. What matters is distinguishing century-old settling that finished moving decades ago from active structural movement — which is a judgment call for someone who works in these homes weekly.

How to budget for the unknown

The standard advice is 'add 20% contingency.' We think that's lazy. The better approach: open up the likely problem areas early — a strategic hole in the right wall costs almost nothing — and base the contingency on what's actually found. Systems first, finishes second: money spent on wiring, plumbing, and structure is invisible but permanent; finishes can phase in later. Our trades in Toronto, Hamilton, and the older cores of Kitchener and Guelph quote with these realities priced in, not discovered.

Keeping the character

The trim profiles, original doors, deep sills, and old-growth floors are why you bought the house — and they're irreplaceable at any reasonable price. Good century-home renovation modernizes everything behind the walls while keeping or faithfully replicating what's in front of them. Note that heritage designations, where they exist, mainly restrict exterior changes; interior renovations are generally unrestricted, but it's confirmed during scoping.