GL InspectionsAluminum wiring and knob-and-tube: what are the risks and what should I do?
Both can be safe when properly maintained, according to Ontario's Electrical Safety Authority (ESA), but both need an assessment by a Licensed Electrical Contractor. Aluminum wiring's risk is at loose or incompatible connections; knob-and-tube is old, ungrounded wiring that many insurers will not cover without replacement or an inspection.
Updated October 2026 · By Gerardo Lucero, Certified Professional Inspector (CPI)
Two old wiring types, two different problems
Buyers often hear "old wiring" and assume the worst. In practice, aluminum wiring and knob-and-tube are very different systems from different eras, and they are handled differently by electricians and insurers. Here is how they compare.
| Aluminum branch wiring | Knob-and-tube | |
|---|---|---|
| When it was used | Homes built mid-1960s to late 1970s | Early 1900s to the 1940s |
| Typical GTA homes | Bungalows, backsplits and early subdivisions of that era | Older pre-war houses in Toronto neighbourhoods |
| What it looks like | Silver-coloured solid wire; cable jacket may be marked "AL" | Single cloth- or rubber-covered wires run on porcelain knobs and through porcelain tubes |
| Main concern | Connections at outlets, switches and splices can loosen and overheat if devices are not approved for aluminum | No ground wire, aging insulation, past amateur splices, and no modern protection in wet areas |
| ESA position | Safe if proper connections and terminations are made with devices approved for aluminum | Safe if properly maintained by a Licensed Electrical Contractor |
| Insurance | Some insurers will not cover or renew without an ESA inspection | Many insurers will not insure it, or require replacement or an electrical inspection |
| Usual fix | Electrician repairs connections with approved devices and connectors; full rewire not always needed | Often partial or full replacement, especially if the insurer requires it |
One more detail for knob-and-tube: the 2021 Ontario Electrical Safety Code removed the rules for installing it, but the code is not retroactive, so existing knob-and-tube is not automatically illegal. The pressure to replace it usually comes from insurers, not the law.
What I can and can't see on inspection day
Under the InterNACHI Standards of Practice I describe the type of wiring I observe and report solid-conductor aluminum branch wiring when it is readily visible. I look wherever wiring shows: at the electrical panel, in unfinished basement ceilings, in the attic and at a representative number of outlets and switches. Most wiring is hidden in walls, so a visual inspection can't confirm that a house is free of old wiring, or that it was fully removed during a renovation. If I see signs of it, I note it with photos and recommend an assessment by a Licensed Electrical Contractor. You can also read about other electrical panel red flags I look for.
Older homes take longer to inspect. Homes built before 1975 may cost more, as explained in the cost guide.
What to do as a buyer
- Call your insurer during the condition period. Ask directly whether they insure aluminum or knob-and-tube wiring and what they need from you.
- Get a Licensed Electrical Contractor's assessment. In Ontario, only an LEC can legally be hired for electrical work in your home.
- Ask for the ESA Certificate of Acceptance for any repair or rewire the seller says was done.
- Negotiate with real numbers. Use the electrician's quote, within your inspection condition, to ask for a credit or price change.
This is general information, not legal or insurance advice; confirm with your agent, lawyer and insurer.
Looking at a 1960s bungalow or a pre-war house? Book your inspection and I'll show you what I find.
Sources
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Questions people ask
can i get insurance with knob and tube in ontario
Some insurers will not cover it, others give you time to replace it or ask for an ESA electrical inspection. Call your insurer before you firm up the purchase.
is aluminum wiring illegal in ontario?
No. ESA says aluminum wiring is safe when connections are made properly with devices approved for aluminum, but some insurers want an ESA inspection first.
what years did they use aluminum wiring in canada
Mostly in homes built from the mid-1960s to the late 1970s.
do i have to replace all the aluminum wiring?
Not always. A Licensed Electrical Contractor often repairs the connections with approved devices instead of rewiring the whole house, but they will advise after an assessment.
will the home inspector tell me if there's knob and tube?
I report the wiring types I can see, at the panel, in the attic and in unfinished areas. Wiring hidden in walls can't be confirmed visually, so an electrician may be recommended.
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