The original wiring method in homes built before roughly 1950: single insulated copper conductors run individually through ceramic knobs (which hold the wire away from wood) and tubes (where it passes through framing), with no ground wire. It's common in older Canadian housing stock — much of pre-war Toronto and the older Vancouver neighbourhoods — and is often still live in attics, basements, and knee walls. Ontario's Electrical Safety Code removed the installation rules for knob-and-tube in its 28th Edition (2021); the code isn't retroactive, so existing K&T isn't illegal — it's simply no longer a system anyone installs.
$8,000–15,000+ to rewire a typical house (more for larger/finished homes)Address before purchaseElectrical
Why it matters
The Electrical Safety Authority's position is that knob-and-tube is not inherently hazardous if it has been properly maintained and is regularly checked for deterioration — but that's a large "if" in a 70-plus-year-old system. It has no ground, the insulation grows brittle with age, and it becomes genuinely dangerous when buried in modern attic insulation (it was designed to shed heat into open air), spliced into by amateurs, or overloaded by today's appliances. The faster, more certain problem is money: many insurers will not write or renew a policy on a home with active knob-and-tube, and some require full replacement before binding coverage, which can in turn complicate your mortgage. That makes it a before-you-buy issue.
How to spot it
Ceramic knobs and tubes with cloth-covered conductors in the attic or basement; two-prong (ungrounded) outlets throughout; a pre-1950 build with no record of a rewire. Insulation piled over old wiring in the attic is a particular red flag.
What it costs
Roughly $8,000–15,000+ to rewire a house, depending on size, finishes, and access — a partial home can be less, a large or fully finished home more.
What to do
Address before purchase. ESA recommends hiring a Licensed Electrical Contractor (LEC) to assess how much K&T is still active and its condition, and to do any replacement under an ESA inspection. Critically, ask your insurer or broker about coverage before you remove your conditions — not after. Use the assessment and any quote as a negotiation point.
Education and triage, not a home inspection. Casaroo flags possible knob-and-tube from what's visible in photos — a Licensed Electrical Contractor confirms the true scope and condition.
Common questions
What is Knob-and-tube wiring?
The original wiring method in homes built before roughly 1950: single insulated copper conductors run individually through ceramic knobs (which hold the wire away from wood) and tubes (where it passes through framing), with no ground wire. It's common in older Canadian housing stock — much of pre-war Toronto and the older Vancouver neighbourhoods — and is often still live in attics, basements, and knee walls. Ontario's Electrical Safety Code removed the installation rules for knob-and-tube in its 28th Edition (2021); the code isn't retroactive, so existing K&T isn't illegal — it's simply no longer a system anyone installs.
Why does it matter for home buyers?
The Electrical Safety Authority's position is that knob-and-tube is not inherently hazardous if it has been properly maintained and is regularly checked for deterioration — but that's a large "if" in a 70-plus-year-old system. It has no ground, the insulation grows brittle with age, and it becomes genuinely dangerous when buried in modern attic insulation (it was designed to shed heat into open air), spliced into by amateurs, or overloaded by today's appliances. The faster, more certain problem is money: many insurers will not write or renew a policy on a home with active knob-and-tube, and some require full replacement before binding coverage, which can in turn complicate your mortgage. That makes it a before-you-buy issue.
How can I spot it?
Ceramic knobs and tubes with cloth-covered conductors in the attic or basement; two-prong (ungrounded) outlets throughout; a pre-1950 build with no record of a rewire. Insulation piled over old wiring in the attic is a particular red flag.
How much does it cost to fix?
Roughly $8,000–15,000+ to rewire a house, depending on size, finishes, and access — a partial home can be less, a large or fully finished home more.
Insurer stances vary — confirm with your broker; a licensed electrician confirms condition. Casaroo flags, it does not inspect.
Last reviewed 2026-06-27.
Casaroo reviews each guide against current pricing, code, and insurer practice. Cost ranges are 2026
estimates that vary by region, size, and access — confirm specifics with a licensed professional.