Knob and tube wiring is an early electrical system, installed in Ontario houses from roughly 1900 through the 1940s, that runs separate hot and neutral wires through ceramic knobs and tubes with no ground wire. It matters when buying a house in Toronto because many insurers will not cover a home with active knob and tube wiring, and a financed purchase generally cannot close without home insurance in place.
How knob and tube wiring works
The name comes from the ceramic knobs that hold each wire away from the wood framing and the ceramic tubes that protect it where it passes through a joist. Each circuit uses two single conductors insulated with rubber and cloth. Nothing grounds the system, so outlets cannot safely accept a three-prong plug.
Toronto has a large stock of century houses in areas like Riverdale, Parkdale and the Annex, and original wiring sits behind the plaster in many of them. Age is the real concern. Insulation that is 80 to 120 years old dries out and cracks, and amateur splices or attic insulation packed over the wires can create a fire risk the original installers never anticipated.
What the Electrical Safety Authority says
The Electrical Safety Authority, which administers the Ontario Electrical Safety Code, does not require anyone to remove knob and tube wiring. The Code is not retroactive, and the ESA's position is that the wiring can be safe when it is intact and maintained by a Licensed Electrical Contractor. It does recommend an electrical assessment by one, separate from a general home inspection.
Why insurers treat it differently
Insurance is where the difficulty sits. A number of Ontario insurers decline new policies on houses with active knob and tube. Others will bind coverage only if the wiring is replaced and certified within 30 to 90 days of closing, while a few charge a higher premium for as long as it remains. Since a lender requires proof of coverage before advancing funds, a buyer should confirm that home insurance can be arranged before waiving conditions.
Rewiring a typical detached Toronto house runs about $12,000 to $20,000 when the walls are already open for a renovation, and $20,000 to $32,000 as a standalone job. A panel upgrade to 200 amps often adds $2,800 to $4,500. The work must be filed with the ESA and pass inspection, producing a Certificate of Acceptance that insurers will ask to see.
Knob and tube is usually visible in an unfinished basement and a home inspector will flag it, much like Kitec plumbing in a condo. Where a seller knows of hidden wiring that affects safety or insurability, it may also be a material fact that should be disclosed.
Related reading: Do You Need Home Insurance to Get a Mortgage in Ontario?, What Is a Material Fact in Ontario Real Estate?, and What Is Kitec Plumbing and Why Does It Matter When Buying a Condo in Toronto?
