Knob and tube wiring is present in a large number of older Toronto homes — particularly in neighbourhoods like The Annex, Roncesvalles, High Park, Riverdale, and East York, where much of the housing stock predates the 1950s. Whether it's a safety concern depends on its condition, how it's been modified over the decades, and how your home is insulated.
What Is Knob and Tube Wiring?
Knob and tube (K&T) wiring was the standard residential wiring method in Canada from roughly the 1880s through the 1940s. It consists of single copper conductors run through ceramic "knobs" (anchors) and ceramic "tubes" (where wire passes through framing members). The conductors are insulated with rubber covered by cloth braid.
The system has no ground wire — only hot and neutral conductors. This means K&T circuits cannot support three-prong grounded outlets or modern appliances that require a ground.
Is Knob and Tube Wiring Dangerous?
Knob and tube wiring isn't inherently dangerous if it was properly installed, has never been modified, and exists in an uninsulated space. The original design relied on air cooling around the conductors — the open air space in walls and attics allowed heat to dissipate safely.
The problems arise from several common situations:
- Insulation in contact with the wire. When homeowners or contractors added blown-in insulation to walls and attics without removing the knob and tube, the wiring lost its ability to cool. Insulation covering K&T is a fire hazard and violates current code.
- Deteriorated insulation. The rubber and cloth insulation on knob and tube wire has a finite lifespan. After 60–100 years, it often becomes brittle, cracks, and flakes — leaving bare conductors in walls and ceilings.
- Improper modifications. Over decades, homeowners and unqualified workers spliced new wiring into K&T using incorrect methods — cloth tape instead of junction boxes, wrong wire gauges, or reversed polarity. These modifications are often hidden inside walls.
- Over-fused circuits. Knob and tube was typically rated at 15A. When fuse boxes were replaced over the years, some circuits were put on 20A or 30A breakers — more current than the wire was designed to carry.
Why Does It Affect Insurance?
Most Ontario home insurance companies are cautious about knob and tube wiring — some refuse to insure homes with active K&T, and others charge significantly higher premiums. The insurance industry's concern is the combination of aging insulation, unknown modifications, and the inability to accommodate modern electrical loads safely.
When buying or selling a Toronto home with knob and tube wiring, this is routinely flagged by home inspectors and addressed during negotiations.
When Does Knob and Tube Need to Be Replaced?
Replacement is generally recommended when:
- Your insurance company requires it as a condition of coverage
- The wiring has insulation in contact with it (blown-in insulation, batts)
- The insulation on the wire is visibly deteriorated or cracked
- There are signs of improper modifications
- You're renovating and opening up walls anyway
- You want to add modern grounded outlets or new circuits to the space
What Does Knob and Tube Removal Involve?
The scope depends on how much K&T exists and where it's located. Partial removal addresses specific areas — the attic, one floor, or specific circuits. Full removal replaces all K&T throughout the house with modern NMD90 (Romex) wiring.
The work typically involves opening walls and ceilings to access and replace the old wiring, installing grounded outlets, and updating the panel connections. In some cases, a panel upgrade is done at the same time to bring service up to 200A.
All K&T removal work is ESA-permitted and inspected. The permit is filed before work begins, and the inspection happens after the work is complete.
Get an Honest Assessment
If you have knob and tube wiring in your Toronto home and aren't sure what action to take, we'll give you an honest assessment — not a sales pitch. In some cases, the wiring is in good condition and partial remediation is sufficient. In others, full replacement is the right call. We'll tell you which applies to your home.