Knob-and-Tube and Aluminum Wiring in Toronto Homes: What Buyers Need to Know

Knob-and-tube wiring was used in Ontario homes from the early 1900s to the 1940s, and aluminum branch wiring shows up in homes built from the mid-1960s to the late 1970s, according to the Electrical Safety Authority (ESA). Neither is automatically unsafe, but many insurers will refuse, limit or price up coverage on homes that have them. If you're buying an older home in Toronto, find out what wiring it has, get an insurance quote and an electrician's assessment before your conditions expire.

What Is Knob-and-Tube Wiring?

Knob-and-tube wiring is an early electrical method that runs single wires through ceramic knobs and tubes, rather than inside a sheathed cable, and the ESA dates it to homes built from the early 1900s to the 1940s. ESA now calls it "open wiring."

You'll recognize it by:

• Separate wires spaced apart, held off the framing by white ceramic knobs, often visible in an unfinished basement or attic
• Ceramic tubes where wires pass through joists or studs
• Cloth-covered insulation on the individual conductors
• No ground wire, which usually means two-prong outlets on those circuits

The 28th Edition (2021) of the Ontario Electrical Safety Code (OESC) deleted the installation rules for knob-and-tube, so it can't be installed new. But ESA's Flash 25-05-FL is clear that "the OESC is not retroactive," so existing knob-and-tube does not have to be removed by default.

What Is Aluminum Wiring?

Aluminum wiring is branch-circuit cable with aluminum conductors instead of copper, and ESA says you may have it if your home was built between the mid-1960s and the late 1970s. The OESC still permits aluminum wiring, and ESA states it "is safe if proper connections and terminations are made without damaging the wire."

From the outside, aluminum cable looks like ordinary sheathed copper cable. The U.S. Consumer Product Safety Commission's Repairing Aluminum Wiring guide says the easiest way to tell is the printing on the cable jacket: aluminum cable is marked "Al" or "Aluminum," and you can often read it in an unfinished basement, attic or garage. Some homes have a mix of aluminum and copper, as ESA's Flash 19-30-FL notes.

The problem is at the connections, not the wire itself. ESA explains that aluminum tends to oxidize and is incompatible with devices rated only for copper, which can lead to overheating and failure at terminations.

Knob-and-Tube vs Aluminum Wiring at a Glance

This table compares the two wiring types buyers most often ask about, using ESA guidance unless noted.

Why Do Insurers Care About Old Wiring?

Insurers care because they see these systems as higher risk. ESA says many insurers will not provide or renew coverage on homes with knob-and-tube because "they consider it to be a higher risk," and some require the wiring to be replaced before they'll offer a policy.

For aluminum wiring, ESA says some insurers won't provide or renew coverage without an ESA inspection, and you may need to repair or replace the wiring and give the insurer a copy of the ESA Certificate of Acceptance.

A February 2024 article in Canadian Underwriter, an insurance trade publication, reported that most insurers treat knob-and-tube, aluminum wiring and 60-amp electrical service as high-risk. The master electrician quoted in that piece argued that the bigger hazards are often a lack of grounding and unpermitted additions by unqualified people, rather than the original wiring. That's one expert's view, not an insurer policy, so the practical rule stands: ask your insurer what it requires before you firm up.

Policies differ between insurers, so the only reliable answer for a specific house comes from a written quote. Check with your insurer or broker.

What Does ESA Say About Keeping or Fixing Old Wiring?

ESA says existing knob-and-tube may stay in service under specific conditions, and aluminum wiring is acceptable once its connections are made with aluminum-rated devices or copper pigtails by a Licensed Electrical Contractor.

Keeping knob-and-tube

According to ESA Flash 25-05-FL, concealed knob-and-tube conductors supplying general lighting and receptacle circuits may remain if:

1. They are protected by a 15 A fuse or circuit breaker
2. No added outlets overload the circuit
3. The visible conductors appear to be in good condition

ESA recommends that a Licensed Electrical Contractor (LEC) inspect the wiring, and that conductors be replaced where exposed wiring shows mechanical abuse, deterioration, poor connections, overheating, overloading alterations or work that doesn't meet the OESC.

The same Flash lists practices ESA considers unsafe:

• Replacing 15 A fuses with 20 A or 30 A fuses
• Using extension cords as permanent wiring
• Adding outlets to existing knob-and-tube circuits (LEC work only)
• Removing ground pins from power bars or using two-pin to three-pin adapters

Any modification needs a notification of work filed with ESA under OESC Rule 2-004, and ESA advises having an LEC do the work and arranging an ESA inspection.

Making aluminum wiring safe

Aluminum wiring is made safe by fixing the connections. ESA Flash 19-30-FL "strongly recommends" replacing original devices with properly marked aluminum-rated devices or installing copper tails (pigtails), done by an LEC experienced with aluminum.

The device markings ESA lists include:

ESA also says push-in (back-stab) terminations must not be used with aluminum, and that devices previously swapped for copper-only types, such as some Decora-style switches, must be replaced with Cu/Al devices. Warning signs ESA lists include warm cover plates, discoloured switches or receptacles, flickering lights and the smell of hot plastic.

US guidance is stricter. The CPSC treats CO/ALR devices as a temporary fix and prefers COPALUM crimp pigtails or AlumiConn connectors. It also cites a survey that found pre-1972 aluminum-wired homes were 55 times more likely than copper-wired homes to have at least one outlet connection reach "fire hazard conditions." In Ontario, ESA and the OESC set the rules, and your insurer may set its own on top. Ask both what they'll accept.

What About Ungrounded Two-Prong Outlets and 60-Amp Service?

Two-prong outlets usually mean the circuit has no ground, and ESA says you can't simply swap them for three-prong outlets. Under OESC Rule 26-702, as explained in ESA Flash 25-05-FL, a three-pin receptacle either needs a bonding conductor to ground, or it must be protected by a Class A GFCI (ground fault circuit interrupter). ESA adds that a GFCI does not provide a ground reference to the third slot, and some equipment, such as surge protectors for computers and entertainment systems, needs that ground.

Watch for these on a showing:

• Three-prong outlets on an old house with no visible ground wiring. They may have been swapped without a ground or GFCI.
• Two-pin to three-pin adapters plugged in throughout the home.
• Fuse panels with 20 A or 30 A fuses on what look like lighting circuits.

As of October 2026, ESA's current Flash (May 2025) also lists GFCI protection for outdoor receptacles, bathroom and washroom receptacles, and kitchen receptacles within 1.5 m of a sink when new outlets are installed.

On service size, Canadian Underwriter reports that most insurers view 60-amp service as high-risk. Whether a larger service makes sense depends on the home's loads and your plans (a heat pump, EV charger or basement suite adds demand), so ask an electrician. In Toronto, a service upgrade also involves the utility: Toronto Hydro says it contacts you within 10 business days of a request, a Job Quotation or Offer to Connect can take up to 60 days once it has all required information, and you or your contractor must complete an ESA inspection before Toronto Hydro upgrades the service.

How a Home Inspection Handles Old Wiring

A home inspection is visual, so an inspector can flag signs of knob-and-tube or aluminum wiring but can't confirm how much is in the walls or whether it's still live. Here's how the split works on a Quality Inspections pre-purchase inspection:

If the report flags possible knob-and-tube or aluminum wiring, the next step is a Licensed Electrical Contractor. ESA itself makes this distinction: an LEC assessment "is different than a home inspection because it only focuses on the electrical," according to the ESA. Quality Inspections does not perform ESA electrical inspections.

For a broader look at what's covered, see what a home inspector checks in Ontario.

What Should You Do Before Firming Up?

Before you waive your conditions on a house with old wiring, get three things in writing. A conditional period is often only a few business days, so start early.

1. Book the home inspection early. It tells you where to look: visible knob-and-tube, aluminum cable markings, the panel, two-prong outlets and alterations.
2. Get an insurance quote on the actual address. Tell the insurer or broker what the inspection found. Ask whether they'll cover it as-is, whether they need an ESA certificate, and whether they require replacement by a deadline.
3. Get an LEC to assess the wiring and quote the work. Ask what's active, what needs replacing, and whether a service upgrade makes sense. Repair costs vary widely by house, so rely on written contractor quotes.
4. Talk to your real estate lawyer about using the findings to renegotiate, ask for a credit, or walk away within your conditions.

If you're buying in a competitive situation, a pre-offer inspection lets you learn about the wiring before you submit. The checklist for first-time buyers in Toronto covers what else to line up.

Where Is Old Wiring Common in the GTA?

Old wiring is most likely in Toronto's pre-war and post-war neighbourhoods, and the City's data shows how much older stock there is. According to the City of Toronto's 2016 household profiles, about one in three Toronto households (33%) lived in dwellings built before 1960, and another 31% lived in dwellings built from 1961 to 1980.

Those two periods line up with the wiring eras ESA describes:

• Pre-1950 houses in Toronto's older neighbourhoods are where knob-and-tube is most likely to be found, sometimes partly replaced and partly still active.
• 1960s and 1970s houses in Toronto's inner suburbs, and in older parts of Burlington and Oakville, fall in the aluminum-wiring window.

Many older GTA homes have been partly rewired over the decades, so the age of the house is a starting point, not an answer. A 1920s Toronto semi might have a new panel and mostly copper, with one knob-and-tube circuit still live in the attic. Quality Inspections inspects older homes across Toronto, Oakville and Burlington.

Frequently Asked Questions

Is knob-and-tube wiring illegal in Ontario?

No. The 2021 OESC removed the rules for installing new knob-and-tube, but ESA says the code is not retroactive, so existing wiring can remain if it's properly maintained and meets ESA's conditions.

Can I get home insurance with knob-and-tube wiring in Toronto?

Sometimes, but many insurers won't provide or renew coverage, and some require replacement first, according to ESA. Get a written quote on the specific address before you firm up.

Is aluminum wiring safe?

ESA says aluminum wiring is safe when connections and terminations are made properly with devices approved for aluminum. Original copper-only devices and push-in connections are the main concern.

Can I replace two-prong outlets with three-prong outlets?

Only if the outlet is grounded with a bonding conductor or protected by a Class A GFCI, under OESC Rule 26-702 as explained in ESA Flash 25-05-FL. Two-pin to three-pin adapters are not permitted.

Can a home inspector confirm the house has no knob-and-tube?

No. A home inspector can only report what's visible and accessible. Wiring hidden in walls and ceilings needs a Licensed Electrical Contractor to assess.

Who do I call to fix old wiring in Ontario?

A Licensed Electrical Contractor, who files a notification of work with ESA and has the work inspected. Ask for a copy of the ESA certificate for your insurer.

Sources

• Knob and Tube Wiring — Electrical Safety Authority
• Aluminum Wiring — Electrical Safety Authority
• Flash 25-05-FL: Knob and tube wiring in residential installations — Electrical Safety Authority
• Flash 19-30-FL: Aluminum wiring in residential installations — Electrical Safety Authority
• Repairing Aluminum Wiring — U.S. Consumer Product Safety Commission
• Managing insurer concerns about knob-and-tube wiring — Canadian Underwriter
• Service upgrade request — Toronto Hydro
• 2016 Household Profiles — City of Toronto City Planning

Book an Inspection

Buying an older home in Toronto, Oakville or Burlington? Call (416) 899-8116 or send the property details and book a pre-purchase inspection. You'll get a digital report with photos within 24 hours, in time to line up your insurance quote and electrician.