If your home was built before the 1950s, it may hide old “knob and tube” wiring. Here’s how to recognize it, why it worries insurers, and what to do about it.
Knob and tube, explained
It’s the wiring method of old houses: individual wires held by porcelain knobs and passed through ceramic tubes across the joists. It served its era well — but this system has no ground and was never designed for today’s electrical needs.
Why it worries people
No ground
No ground wire means no shock protection for your modern appliances.
Aging insulation
After 70-100 years, the wire’s sheathing dries out, cracks and crumbles — a risk of arcing and fire.
Accumulated DIY
Decades of amateur changes (splices, dubious connections) weaken the whole thing.
Smothered by insulation
Covered by blown-in attic insulation, old wire overheats — it wasn’t designed for that.
Overloaded
Built for a few light bulbs, not today’s kitchens, appliances and electronics.
Refused by insurers
Like aluminum, many insurers require an inspection… or its replacement.
Do you have knob and tube?
- Individual wires running over small white porcelain cylinders, visible in the basement or attic.
- Two-prong outlets (no ground slot) throughout.
- A house built before ~1950 that has never been rewired.
The crux of the matter
Knob and tube is, along with aluminum, one of the most scrutinized points when buying and by insurers. Some refuse to insure, others require an inspection or replacement. Finding out before buying (or before a renewal) avoids nasty surprises — and gives you a bargaining chip.
You don’t “repair” it, you replace it
There’s no real patch for knob and tube: the right approach is replacing the wiring with modern, grounded cable, often zone by zone to spread the budget. We prioritize critical areas (kitchen, bathroom, panel) and bring it all up to code — and insurable.
Knob and tube, aluminum or modern?
Knob and tube
Before ~1950. Wires on porcelain, no ground. Watched by insurers.
Aluminum
1960s-70s. The danger comes mostly from connections that heat up. See our aluminum guide.
Modern copper
Today: sheathed cable with a ground wire, GFCI/AFCI breakers. The safe standard.
How much does rewiring cost?
There’s no single price: it all depends on the size, the access (open or closed walls, accessible basement and attic) and the scope. The good news is you can go zone by zone to spread the cost: start with critical areas (panel, kitchen, bathroom), then the rest over time. We price each step clearly, with no surprises.
From old wire to safe wiring
CMEQ-certified company holding an RBQ licence. We assess your installation, price the replacement and modernize cleanly. Serving Greater Montréal, Laval, the North Shore, the Laurentians and Lanaudière.
An old home to make safe?
We check your wiring and tell you straight whether to act. Free quote.
What homeowners ask us
Is knob and tube wiring dangerous?+
It can become so with age: crumbling insulation, no ground, overloads and accumulated DIY increase the risk of arcing and fire.
How do I know if my house has it?+
Look for wires on small white porcelain cylinders in the basement or attic, two-prong outlets, and pre-1950 construction. An inspection confirms it.
Can my insurance refuse it?+
Yes. As with aluminum, many insurers require an inspection, a higher premium, or outright replacement of the wiring.
Can it be repaired, or must it all be replaced?+
There’s no durable patch. The right solution is replacement with modern grounded wiring, often done zone by zone.
Can a house be rewired without demolishing it?+
Often yes, largely. New wiring runs through accessible spaces (basement, attic, open walls), keeping openings to a minimum.
Can I add insulation over knob and tube?+
No, it’s dangerous: this old wire needs air to dissipate heat. Covered by insulation, it overheats — a common non-compliance and a real fire risk.
Is knob and tube wiring illegal?+
Not in itself if intact and unmodified, but it’s often deemed unsafe, refused by insurers and required to be replaced during renovations.
How long does a full rewire take?+
From a few days to a few weeks depending on the home’s size and access. Going zone by zone limits disruption and spreads the work.
