What Is Knob and Tube Wiring and Should I Replace It?

Knob and tube (K&T) wiring is the oldest style of residential electrical wiring still found in Ontario homes — installed from the 1880s through the 1940s, and remarkably still functional in some early Toronto and East York homes almost 100 years later. The problem is that K&T was engineered for a world without dishwashers, air conditioners, or 240 V ranges, and every insurer in Ontario treats it as a replacement item today. This guide walks GTA homeowners through what knob and tube wiring is, whether it should be replaced, and what the process actually looks like in 2026.

Short answer: yes, plan to replace it

Direct answer: knob and tube wiring should be replaced with modern NMD-90 copper wiring when found in an Ontario home. K&T has no equipment ground, uses single-conductor cloth insulation that degrades with age and heat, and is not compatible with modern loads. Insurance carriers in Ontario increasingly refuse coverage on unremediated K&T, and home inspectors flag it on every purchase.

What knob and tube actually looks like

• Two separate insulated conductors (hot and neutral) running parallel through the framing.
• White ceramic knobs where the wire is supported on the sides of joists or studs.
• White ceramic tubes where the wire passes through drilled holes in wood framing.
• Cloth or rubber-and-cloth insulation around each conductor.
• No bare copper equipment ground. Modern grounding did not exist when K&T was installed.
• Often installed in attics and unfinished basements where it is still visible.

Why it is a real problem today

• No equipment ground. Modern three-prong receptacles cannot be safely installed. Two-prong receptacles are still legal but limit modern appliances.
• Cloth insulation degrades. Age, heat, mice, and moisture crumble the cloth insulation over decades.
• Buried in insulation. Modern attic insulation (blown cellulose, fibreglass batts) traps heat around K&T. Section 12 of the Ontario Electrical Safety Code prohibits K&T inside thermal insulation.
• Cannot handle modern loads. K&T conductors are typically 14 AWG on 15 A circuits, but the branch layout was designed for a few lightbulbs and one appliance, not a modern kitchen or laundry.
• DIY modifications compound risk. Many homes have decades of homeowner and handyman splices onto K&T — each splice is a code violation and a potential failure point.

Insurance situation in Ontario (2026)

Direct answer: most Ontario carriers now require full K&T removal before renewing coverage. Some smaller carriers offer coverage with K&T if a licensed electrician certifies it is not buried in insulation and has been inspected. Even those carriers charge substantial premiums.

The Electrical Safety Authority lists K&T-related residential incidents in the annual Ontario Electrical Safety Report. The category is small in absolute numbers but severe per incident — typically insulation-fed fires that spread rapidly.

Replacement options

• Full replacement with NMD-90 copper. Every K&T conductor is removed and replaced with modern cable. Cost: $12,000-25,000 in the GTA for a typical single-family home.
• Selective replacement. Only the K&T inside insulation or serving high-load circuits is replaced; visible attic and basement runs may be left in place with an insurance-approved certification. Less common in 2026 as insurers tighten.
• New service and full rewire together. Bundling with a panel upgrade shares utility disconnect costs. Combined cost: $15,000-30,000.

Our post on whole-house rewiring cost covers the pricing in detail.

What happens during a K&T replacement

1. Assessment and quote. Contractor maps the extent of K&T, condition, and circuit layout.
2. ESA permit filed. Every K&T remediation requires an inspection.
3. Utility disconnect if the service panel is also being replaced.
4. K&T removed circuit by circuit. Contractor pulls old conductors out through the walls and ceilings.
5. New NMD-90 fished through the framing. Modern cable with equipment ground.
6. New devices installed with grounded three-prong receptacles.
7. Drywall damage patched around new access holes.
8. ESA inspection. Sign-off before final energization.
9. Insurance certificate issued for the homeowner’s records.

DIY K&T removal? Almost never

Direct answer: K&T removal is not homeowner-permitted work in Ontario because the extent of change (removing branch wiring, changing service configuration, adding equipment grounds throughout the house) requires a licensed contractor. Even sophisticated DIYers should hire a professional for K&T remediation.

The scale of change also crosses into building permit territory in some Ontario municipalities — the electrical inspection is coordinated with a building permit review if drywall opening is extensive.

Expert tip from our ESA-licensed electricians

In our experience remediating knob and tube across the GTA — particularly in older Toronto neighbourhoods like The Junction, Leslieville, and East York where 1920s-era homes still have original wiring — the single detail that saves customers the most cost is bundling the rewire with a broader renovation. Homeowners planning a kitchen renovation, a basement finish, or a second-storey addition should schedule the K&T removal to happen at the same time. Sharing the drywall work between two trades cuts $3,000-6,000 off the total. Homeowners who do standalone K&T removal end up paying for the same drywall repair twice — once for the electrical, once for the renovation. Same lesson as the panel-upgrade-plus-rewire combo. Our post on rewire cost covers the bundling math.

Related reading from ezsmart.ca

• Cost to rewire a whole house
• Is aluminum wiring dangerous?
• Signs house needs rewiring
• Do I need a panel upgrade?
• Fuse box vs breaker box

Contact us

Knob and tube wiring in your GTA home? Book an ESA-certified electrician to assess and quote a replacement. Call us at 416-838-9006 or visit our contact page — we will get back to you the same day.