Why insurers care
Knob and tube was installed until roughly the 1940s. Nearly a century on, insulation can be brittle, there's no ground conductor, and many systems have been extended by amateurs. Insurers price that risk — some won't write a new policy until it's gone.
What they usually ask for
- Confirmation that no knob and tube is energized (abandoned, disconnected wiring is generally acceptable)
- An ESA Certificate of Acceptance for the replacement work
- Sometimes a letter from the electrical contractor describing what was replaced
Partial or full?
If previous owners already replaced most circuits, the remaining live knob and tube may be limited to a few runs — a partial job of a few days. If the whole house is original, expect a full rewire.
Costs and timing
In the GTA a full rewire of a semi or row house typically costs $12,000 – $22,000; a detached two-storey $18,000 – $35,000. Most homes take one to three weeks, and you can usually live there throughout.
Buying a house with knob and tube
Get an electrical inspection during your conditional period, call your insurer before you firm up, and price the replacement into your offer. See knob and tube replacement.
Quick questions
Can I get insurance while the work is booked?
Some insurers will bind a policy with a deadline for replacement if you can show a signed contract. Ask yours directly.
Does old wiring left in the walls count?
Generally no, as long as it's fully disconnected from power. Insurers care about energized knob and tube.
How do I know if any is still live?
An electrician can trace and test circuits from the panel and in the attic and basement, where most remaining runs are visible.
