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.
$10,000 to $25,000 to rewire a typical GTA house (smaller homes from ~$8,000; large heritage $35,000+)Address before purchaseElectrical
The quick answer
Knob-and-tube is the ungrounded pre-1950 wiring still live in many older Canadian homes. It isn't illegal, but many insurers won't cover a home that still has it active, which can stall your mortgage, so it's a before-you-buy issue. A full rewire runs about $10,000 to $25,000+. Have a licensed electrician confirm how much is live, and check insurability before you remove your conditions.
You are reading the knob-and-tube wiring page. Type the year the house was built and I will tell you what else tends to be true at that age, what it costs, and what to ask. One number, ten seconds.
Free. No account. Educational and impartial, not a home inspection.
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
Current GTA guides put a typical full rewire at $10,000 to $25,000, smaller homes from ~$8,000, large or heritage homes $35,000 to $50,000. Drywall repair afterwards adds $500 to $5,000. Substantially cheaper if walls are already open during a renovation.
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
How much does it cost to replace knob-and-tube wiring?
Rewiring a typical house runs $10,000 to $25,000+, with smaller homes starting lower and large heritage homes reaching $35,000 to $50,000. Budget $500 to $5,000 on top for drywall repair after the walls are opened. Get quotes from a licensed electrician, the price depends on access and how much of the original wiring remains live.
Will insurance cover a house with knob-and-tube?
This is the fastest-moving problem, faster than the safety question. 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 then complicate your mortgage. Ask your broker about the address before your conditions come off.
Is knob-and-tube illegal?
No. Ontario's Electrical Safety Code removed the installation rules in its 28th Edition, but the code is not retroactive, so existing knob-and-tube is not illegal. It is simply a system nobody installs any more, and one the ESA says is not inherently hazardous if properly maintained and regularly checked, which is a large if in a seventy-year-old system.
Does all of it have to be replaced?
A licensed electrical contractor's first job is to work out how much is actually still live, because in many homes only part of the original wiring remains in service. A full rewire runs $10,000 to $25,000+, and it is substantially cheaper if walls are already open for a renovation.
What makes knob-and-tube actually dangerous?
Three things: burial in modern attic insulation, since it was designed to shed heat into open air, amateur splices into the original runs, and overloading by modern appliances on a system with no ground. Insulation piled over old wiring in the attic is the red flag to act on.
Insurer stances vary. Confirm with your broker; a licensed electrician confirms condition. Casaroo flags, it does not inspect.
Last reviewed 2026-07-10.
This guide is general education, not a home inspection and not advice for your specific property. Always
consult the appropriate licensed professional, and get a licensed home inspection before you remove conditions
or buy. Cost ranges are 2026 estimates that vary by region, size, and access; confirm specifics with a
qualified professional.