Knob-and-Tube Wiring in Older Toronto Homes: A Buyer's and Seller's Guide

Step 1: Understand what it is and whether it's legal

When I tour a pre-1950s home in the GTA, the wiring is the first thing I look at. Knob-and-tube (K&T) runs electrical conductors through ceramic knobs that hold the wire away from framing and ceramic tubes where wires pass through joists. According to the Electrical Safety Authority (ESA, 2021), this method was used in homes built from the early 1900s through the 1940s and is no longer installed today.

The first thing most buyers ask is, “Is this illegal — can I even buy it?” Let me correct that premise first: K&T is not illegal in itself. ESA (2021) explains that while Ontario’s latest electrical code (the OESC 28th Edition, 2021) deleted the installation rules for K&T, the code is not retroactive — existing K&T in an older home is allowed to remain, provided it’s in good condition and hasn’t been improperly modified. The real issue isn’t legality; it’s whether insurers will cover it and whether lenders will get comfortable.

Step 2: Understand the insurance hurdle — it's the real bottleneck

In the older-home deals I’ve handled, what stalls them is almost never the law — it’s insurance. ESA (2021) states it plainly:

Many insurers will not provide or renew coverage on homes with this type of wiring, and some insurers may make you replace the knob and tube wiring before they provide coverage.

That lines up with the Insurance Bureau of Canada (IBC): some insurers won’t cover a K&T home at all; some give you a window of time to replace it; and some will write a policy only after a satisfactory electrical inspection. In my experience you can run into any of the three, depending on the insurer and how much active K&T is present.

Why this step matters: without home insurance, most lenders won’t fund the mortgage. So what looks like a “wiring problem” becomes an “insurance problem,” which becomes a “financing problem.” Before writing an offer, I have buyers get a quote and confirm a carrier will actually bind coverage.

Step 3: Get a licensed electrician's ESA-aligned assessment — don't guess

Whether a given K&T system can stay or must go shouldn’t be decided by eye or by a seller’s reassurance. ESA’s (2021) recommendation is clear: hire a Licensed Electrical Contractor (LEC) to assess the whole electrical system, check the K&T conductors for deterioration or damage, and advise whether replacement is needed.

I flag these common red flags for clients:

• No grounding conductor — a structural limitation of K&T that can’t be patched away simply;
• Improper later modifications — many incidents come not from original K&T but from decades of DIY splices and added loads by non-professionals;
• Cracked, brittle insulation, or wiring buried in blown-in attic insulation (K&T sheds heat through open air and can overheat when covered);
• Low service capacity — these homes often still have an old 60-amp fuse panel that can’t support modern demand.

A written assessment is what gives you something concrete to take to insurers, the seller, and your lender.

Step 4: Price the replacement and process before you decide how to offer

If the assessment says replacement is needed, the next move is to run the numbers. According to Kolji Bros. Electrical (2026), whole-home rewiring in Ontario typically runs:

• Small home (800–1,200 sq ft): about CAD $8,000–$12,000;
• Medium home (1,200–2,000 sq ft): about CAD $12,000–$18,000;
• Large home (2,000–3,000 sq ft): about CAD $18,000–$25,000.

On top of that, a panel upgrade (100A to 200A) runs about CAD $1,400–$1,800, and ESA inspection and permits about CAD $200–$500 (figures also from Kolji Bros. Electrical, 2026). I want to be clear: these are market ranges, not a quote. Actual cost varies widely with square footage, whether walls are already open, and access difficulty — always rely on a licensed electrician’s site-specific estimate.

Process-wise, K&T replacement is permitted work that requires an electrical permit and ESA inspection, handled by a licensed contractor who files the notification and obtains sign-off. The ESA certificate you receive at the end is often exactly what an insurer needs to bind coverage.

If you’re the buyer:

• Make the electrical inspection and insurability a condition of purchase — for example, “conditional on a home inspection and an insurance quote satisfactory to the buyer” — so you have an exit;
• Confirm with an insurance broker, before you offer, that a carrier will cover the home and at what premium;
• Use a written replacement quote as leverage to negotiate price, or to ask the seller to complete the rewire and provide an ESA certificate before closing.

If you’re the seller:

• Option A: rewire and obtain the ESA certificate before closing, making the home insurable and financeable for a wider buyer pool — this usually means a smoother sale and a better price;
• Option B: keep the K&T but have a current electrician’s assessment ready, price the home accordingly, and be transparent with buyers;
• Either way, disclosing known electrical conditions honestly is the baseline — concealment only invites disputes later.

My overall view: a K&T home isn’t a “do not touch” property — it’s a “do the math first” property. Line up inspection, insurance, and cost up front, and the wiring can become negotiating room rather than a deal-breaker.

Can you still get home insurance on a house with knob-and-tube wiring?

Sometimes, but it's not guaranteed. According to ESA (2021), many insurers will not provide or renew coverage on K&T homes, and some require replacement first. The Insurance Bureau of Canada notes some insurers refuse outright, some allow a window to replace it, and some require a satisfactory inspection. Get an insurance quote before you make an offer.

Is knob-and-tube wiring illegal in Ontario?

No. According to ESA (2021), Ontario's electrical code (OESC 28th Edition, 2021) deleted the installation rules for K&T, but the code is not retroactive, so existing K&T may remain if it is in good condition and has not been improperly modified.

How much does it cost to replace knob-and-tube wiring?

According to Kolji Bros. Electrical (2026), whole-home rewiring in Ontario runs about CAD $8,000–$12,000 (small home), $12,000–$18,000 (medium), and $18,000–$25,000 (large), plus roughly $1,400–$1,800 for a panel upgrade and $200–$500 for ESA inspection and permits. These are ranges; rely on a licensed electrician's site-specific quote.

What role does the ESA play with knob-and-tube wiring?

The Electrical Safety Authority is Ontario's electrical safety regulator. According to ESA (2021), it recommends hiring a Licensed Electrical Contractor to assess the system; K&T replacement is permitted work that requires an electrical permit and an ESA inspection, with a certificate issued on sign-off.

As a buyer, should I make knob-and-tube wiring a condition of purchase?

Yes, that's advisable. Making the home inspection and insurability a condition gives you an exit if the wiring or coverage becomes a problem, and a written replacement quote gives you leverage to negotiate price or to ask the seller to rewire and provide an ESA certificate before closing.