Knob-and-tube wiring does not automatically have to be removed from an Ontario house. The Electrical Safety Authority says existing wiring can be safe when properly maintained by a Licensed Electrical Contractor, and the electrical code is not retroactive. That does not settle the decision for your house: damaged or improperly altered wiring can require replacement, and many insurers will not provide or renew coverage on a home that has it. Before deciding to keep it, get an electrical assessment and your insurer’s requirements in writing.
If replacement is needed and you’re renovating anyway, plan it before the walls close. Doing it later can mean reopening the plaster and paint you’ve just finished. The useful question is how much wiring is still live, what the new rooms will need, and which repairs can be done once as part of the renovation.
What knob-and-tube is, and how to recognize it
Knob-and-tube was used in Ontario homes in the early 1900s through the 1940s. Separate insulated copper wires run through the framing, supported by white porcelain knobs and passed through porcelain tubes where they cross wood. The original system has no equipment grounding conductor.
Visible clues in a GTA house built before about 1950 include wires on porcelain knobs along exposed basement joists, porcelain tubes through framing, and old cloth-covered conductors. Two-prong receptacles are a clue to an ungrounded circuit, but a newer three-prong receptacle does not prove that the wiring behind it has been replaced.
Look only at safely accessible, visible areas. Leave panel covers, receptacles, attic insulation and concealed wiring to the Licensed Electrical Contractor. Houses may have been partly rewired, so modern cable in the kitchen does not establish what feeds the upstairs bedrooms. The assessment needs to distinguish abandoned wiring from circuits that are still live.
Is it dangerous?
Age and the wiring label alone do not establish the condition of an installation. ESA identifies deterioration, damage, poor connections, overheating and alterations that overload a circuit as reasons to replace affected conductors. The practical concerns are:
- No equipment ground. The original wiring lacks the grounding and bonding features of a modern installation. GFCI protection may be permitted in some situations, but it does not create a ground connection.
- Aged insulation. Deteriorated or disturbed insulation can expose the conductor.
- Overloading. New loads and added outlets can exceed the original circuit’s capacity. Fitting a larger fuse to stop it blowing defeats the intended protection.
- Wiring covered by insulation. Before adding attic or wall insulation around old wiring, have the contractor assess the wiring and the proposed assembly.
- Improper alterations. Unapproved connections and hidden splices can change an otherwise serviceable circuit.
ESA recommends a Licensed Electrical Contractor’s assessment, which is different from a general home inspection. It examines the electrical system and the work your proposed renovation would require. See ESA’s knob-and-tube guidance and its residential installation bulletin.
Insurance: a separate decision from electrical condition
ESA reports that many insurers refuse or will not renew coverage for houses with knob-and-tube, and some require replacement before providing coverage. A contractor’s assessment can explain the wiring’s condition; it cannot promise that a particular insurer will accept it.
When buying an older house, tell your insurer or broker what has been found before waiving conditions. Ask whether coverage is available, what documentation is required and whether replacement must happen before coverage starts or by a stated deadline. Get those terms in writing. Do the same before renewal or a major renovation; there is no universal replacement deadline that applies to every policy.
What full replacement costs in the GTA
A Toronto electrical contractor’s published December 2025 guide gives $15,000–$30,000+ for full knob-and-tube replacement in a 1,500–2,000 sq ft, two-storey semi-detached or detached home. The guide says patching and repainting may be excluded. This is a published GTA market reference for that scope, not a Capable price or a quote for your house. See the Toronto electrician’s replacement-cost guide.
All figures are in Canadian dollars. Ask whether HST, ESA fees, panel/service work, patching and painting are included; the published range does not establish each inclusion.
On a phone, swipe the table sideways to compare all three columns.
| Factor | Pushes the cost up | Can reduce access or repair work |
|---|---|---|
| Size and storeys | Three storeys, many rooms | Bungalow, open basement ceiling |
| Wall finishes | Plaster and lath, finished ceilings | Walls already open for a renovation |
| Access | Limited attic access, finished basement | Unfinished basement, accessible attic |
| Panel and service | Service or panel upgrade required | Existing capacity suits the new loads |
| Scope | Every circuit, plus new outlets, lighting, EV or range circuits | Keep assessed modern circuits that suit the plan |
| Plaster repair and paint | Separate repair work after the electrician | Coordinate repairs with planned renovation finishes |
Knob-and-tube does not prove that the service is still 60 amps or that a newer panel eliminates old branch wiring. Have the Licensed Electrical Contractor assess both. If a service upgrade is required, the utility connection and inspection steps belong in the plan as well.
The least disruptive moment to do it: during a renovation
Rewiring a finished house requires access through walls and ceilings, then repairs wherever openings were needed. When a renovation is already opening those same areas, the electrician can coordinate new circuits with the kitchen, bathrooms, lighting and other planned loads before finishes go back.
That can reduce duplicated access and repair work. It does not make rewiring or drywall free: areas outside the renovation may still need openings, and the quote should state which repairs are included. Coordinate the required ESA review or inspection before wiring is concealed, then close and finish the affected surfaces once.
Permits and inspections
An ESA electrical notification is separate from a municipal building permit. Almost all electrical work must be reported to ESA; if you hire someone to do it in Ontario, the business must be a Licensed Electrical Contractor. The contractor files the notification and arranges the necessary inspections or review. Ask for the ESA Certificate of Acceptance when the completed work has passed.
The electrical scope and the building work have separate approval paths. If the renovation changes structure, plumbing or other work covered by municipal rules, you may also need a building permit. See ESA’s notifications and inspections guide and our guide to building permits for renovations in Toronto and the GTA.
Buying a pre-1950 house: what to do before you waive conditions
- Ask the home inspector about visible evidence of knob-and-tube and the service size; use a Licensed Electrical Contractor to establish which wiring is live and its condition.
- Get that contractor’s assessment and a written replacement scope with inclusions and exclusions.
- Call your insurer with the findings and get coverage conditions in writing.
- Ask ESA about available electrical records for the property. Records help establish filed work; they do not replace an assessment of today’s condition.
- Price any required rewiring alongside the renovation you’re planning, including access, repairs and work outside the renovated rooms.
A note on aluminum wiring
Houses built from the mid-1960s to late 1970s may contain aluminum wiring. Its repair path differs from knob-and-tube. ESA says each home needs its own assessment by a Licensed Electrical Contractor familiar with aluminum wiring; proper connections and compatible devices matter.
The same December 2025 electrician guide gives roughly $3,000–$6,000 for aluminum connection remediation or pigtailing in an average home, depending on the number of devices. This is a single-source market reference, not proof that this remedy suits your house. The contractor determines whether repair or replacement is appropriate, and your insurer confirms its documentation requirements. See ESA’s aluminum-wiring guidance.
How Capable handles old wiring in a renovation
We’ve renovated Toronto and GTA homes for 25 years. At the estimate visit we look at the panel, the service and the visible wiring so electrical questions enter the drawings and scope before demolition. That initial look does not replace the Licensed Electrical Contractor’s assessment. Electrical work on our projects is done by a Licensed Electrical Contractor and filed with ESA as required.
Drawings and 3D design are included at no charge, and the electrical scope goes into the fixed, itemized renovation quote. Yan, our owner, answers calls at 905-889-0025; use the site’s WhatsApp route to message him.
Planning an older house? Read renovating an older Toronto house: what to check, the full-home renovation planning guide, or start with full-home renovation in Toronto. To discuss the wider renovation, use the existing project enquiry form on this page and mention the house’s city, approximate age and known wiring findings.
Quick answers
Is knob-and-tube wiring illegal in Ontario?
Existing knob-and-tube does not automatically require removal because the code is not retroactive. Its condition, alterations and circuit protection matter. Have a Licensed Electrical Contractor assess it; your insurer may still require replacement.
Can I get home insurance with knob-and-tube wiring in Ontario?
It depends on the insurer and the house. ESA says many insurers refuse or will not renew coverage, and some require replacement first. Ask for the coverage terms, required documents and any deadline in writing before relying on insurance being available.
How much does it cost to replace knob-and-tube wiring in Toronto?
One published Toronto electrician guide from December 2025 gives $15,000–$30,000+ for a 1,500–2,000 sq ft two-storey home; patching and painting may be excluded. Get a property-specific quote, including HST and repair work. Open walls can reduce duplicated access work, without guaranteeing a saving.
Do I need a permit to replace knob-and-tube wiring?
The electrical work uses the ESA notification and inspection/review process. If you hire out the work, use a Licensed Electrical Contractor and ask for the Certificate of Acceptance. A municipal building permit may also be needed for accompanying renovation work; it does not replace the ESA notification.
Can knob-and-tube be left in place if I’m only renovating one room?
Some existing wiring may remain if the installation meets the applicable conditions. Ask the Licensed Electrical Contractor what can stay, what needs replacement and how new loads or insulation affect it. Confirm the plan with your insurer before treating a one-room renovation as the complete solution.
Sources checked October 6, 2026: ESA knob-and-tube guidance and residential bulletin; ESA notifications/inspections and Certificate of Acceptance; ESA aluminum-wiring guidance; the December 4, 2025 Toronto electrician guide. General homeowner information; a Licensed Electrical Contractor assesses your house, and your insurer decides coverage.
