The short answer
Active knob-and-tube is closer to a conditional dealbreaker: fine if you can arrange insurance and budget a rewire, a real problem if you can't. Unlike poly-B, this one can block the mortgage directly, so insurability comes first. Read the full guide to knob-and-tube wiring.
Why buyers worry about it
Knob-and-tube has no ground, its insulation gets brittle with age, and it's dangerous when buried in insulation or overloaded by modern demand. But the bigger buyer issue is insurance: the Insurance Bureau of Canada notes many insurers won't cover it, some give you time to replace it, and some cover it only after a safety inspection.
What insurance really looks like in 2026
Standard carriers — the ones with the best rates — often decline active knob-and-tube outright. Specialty carriers will usually write it subject to an electrical inspection, at premiums commonly 30–50% higher, sometimes on limited (actual-cash-value) terms. In Ontario, the Facility Association is the insurer of last resort if no one else will. Translation: coverage usually exists, but it costs more — factor that in.
What it costs to fix
A full rewire typically runs $8,000–15,000+, depending on the home's size, access, and finishes. Partial removal (just the active circuits, or just what's buried in insulation) can be cheaper and is sometimes enough to satisfy an insurer — ask a licensed electrician.
How to handle it in your offer
- Get an insurance quote on the specific home before you remove conditions.
- Have a licensed electrician confirm how much is active and quote a rewire.
- Use the rewire quote to negotiate price, or make the seller's rewire a condition.
- If no affordable coverage exists and a rewire isn't in budget, this is one of the cases where walking is reasonable.