Two wiring types stop Ottawa real estate deals more often than everything else in the electrical system combined. Neither is straightforwardly "dangerous", and neither is straightforwardly fine. What makes them decisive is that Ontario insurers have opinions about them, and a house you cannot insure is a house you cannot finance.
Knob-and-tube: pre-1950 homes
Knob-and-tube was standard wiring practice from roughly 1900 to the late 1940s. Individual conductors run through ceramic tubes where they pass through framing and are supported on ceramic knobs, with the hot and neutral run separately and spaced apart. In Ottawa it is present in the Glebe, Sandy Hill, Centretown, Hintonburg, Old Ottawa South and East, New Edinburgh and Westboro's older stock.
What is actually wrong with it
- No ground. Two-wire system, so no equipment grounding conductor. Modern appliances and electronics assume one.
- Aged insulation. Rubber and cloth insulation becomes brittle after eighty to a hundred years, particularly where it has been heated.
- It must never be covered with insulation. The system was designed to dissipate heat into open air. Blown-in attic insulation over active knob-and-tube is a genuine fire risk and it is extremely common, because the person blowing the insulation had no idea it was there.
- Amateur splices. Eighty years of modifications, often junction-box-free, buried in walls.
- Capacity. Designed for a house with a radio and a few lamps, not induction ranges and heat pumps.
The insurance reality
Many Ontario insurers will not write a policy on a home with active knob-and-tube. Others will, with a deadline for replacement or a surcharge. This varies genuinely and significantly between carriers, so the only useful answer comes from calling a broker with the specific address — on day one of your conditional period.
What replacement costs
Rewiring a typical Ottawa two-storey century home runs roughly $12,000 to $25,000, more where plaster walls must be opened and restored. Partial rewiring — replacing active knob-and-tube while leaving abandoned runs in place — is often the practical middle path, and an ESA inspection should confirm the result.
Aluminum branch wiring: roughly 1965–1977
During a period of high copper prices, single-strand aluminum was widely used for branch circuits. In Ottawa this lands squarely on a band of housing across Nepean, Gloucester, older Orléans, Bells Corners and parts of early Kanata.
What is actually wrong with it
Not the wire — the connections. Aluminum expands and contracts more than copper with temperature change, it is softer, and it oxidises to a poorly conductive layer. Over decades, terminations at outlets, switches and panels loosen, resistance rises, and the connection heats. Failures happen at terminations, which is why the remediation targets terminations.
How it is properly remediated
- Approved connectors (such as the AlumiConn or COPALUM systems) at every device termination, installed by a licensed electrician.
- Pigtailing with approved connectors and antioxidant compound, so devices see copper.
- CO/ALR-rated devices — better than standard devices, but generally not accepted by insurers on its own as full remediation.
- Full replacement — the definitive answer, at rewiring cost.
Remediation of a typical home runs roughly $1,500 to $5,000 depending on device count. That is a very different number from rewiring, which is why aluminum is a negotiation and knob-and-tube is sometimes a deal-breaker.
How to identify them yourself
Knob-and-tube: look in the attic and the basement for white or brown ceramic knobs supporting single wires, and ceramic tubes where wires pass through joists. The wires are individual, spaced apart, and often cloth-covered.
Aluminum: the conductor is silver rather than copper-coloured. Cable sheathing from the era is frequently marked "ALUMINUM" or "AL". You can sometimes see it at the panel, but do not remove device covers yourself — that is live work.
What to do as a buyer
- Find out what is there — during the inspection, before the condition expires.
- Call an insurance broker immediately with the address and what was found. Get a written answer.
- Get a quote from a licensed electrician for remediation or replacement.
- Negotiate with the quote in hand. A specific number is a negotiating position; "the wiring is old" is not.
- Never accept "it has been fine for eighty years" as an answer. It is true and it is irrelevant — the risk is cumulative and the insurer's position is not sentimental.
Frequently asked
Can you get insurance with knob-and-tube wiring in Ontario?
Some insurers will decline outright, others will write a policy with a replacement deadline or a surcharge. It varies significantly by carrier, so call a broker with the specific property details before your condition period expires.
Is aluminum wiring safe if it has been pigtailed?
Pigtailing with approved connectors and antioxidant compound, done by a licensed electrician throughout the home, is a recognised remediation and is generally accepted by insurers. Partial or improper pigtailing is not, so ask for documentation of the work.
How much does it cost to rewire a century home in Ottawa?
Roughly $12,000 to $25,000 for a typical two-storey, more where plaster walls need to be opened and restored. Aluminum wiring remediation is far cheaper, typically $1,500 to $5,000.