Good breakdown of what really goes wrong during a full renovation. Adding a Canadian/GTA perspective since we have been through this with homeowners across the Toronto area for over 50 years.
The point about old-home surprises rings especially true here. A lot of GTA housing stock dates from the 1960s through 1980s, and once walls open up you are often dealing with knob-and-tube wiring, galvanized plumbing, and insulation that has not been touched in decades. These are not optional upgrades - inspectors and insurance companies will not let you close those walls until the issues are addressed. Budget for them upfront, not as a shock mid-project.
A few things worth adding from the Canadian side:
Permit timing is its own stress category. Toronto has a FASTRACK program for smaller compliant projects, but anything structural or involving HVAC modifications still runs 6 to 12 weeks. Homeowners who have not built that buffer into their timeline discover it the hard way when the contractor is ready and the permit is not.
Spring scheduling pressure compounds everything else. Skilled trades in the GTA book out weeks ahead from March through June. If your project hits delays, you risk losing your contractor slot - not because they do not want to finish, but because their next job is already locked in. Having the “what if we slide two weeks” conversation before you sign anything is worth doing.
The contingency budget advice here is right, but 10% is often too thin for older Ontario homes. For anything built before 1990, we recommend 15 to 20%. The surprises in those houses are essentially guaranteed.
If you are planning a GTA renovation and want a gut check on scope or budget, feel free to post questions here or check out our community FAQ for more.