Knob-and-tube wiring: what it means for your insurance, your reno, and your house

If your house was built before the 1950s, somewhere between Kitsilano and Chilliwack there’s a decent chance it still carries some knob-and-tube: single copper conductors running through ceramic knobs and tubes in the joists. We open up walls in old homes every month, and it’s still in there more often than owners expect.

How to spot it

Look in the attic, the crawlspace, or the unfinished part of the basement ceiling. Knob-and-tube runs as two separate wires spaced apart, held off the wood on white ceramic knobs, passing through ceramic tubes where they cross joists. Two-prong outlets throughout the house are another hint, though not proof on their own.

Is it dangerous?

Here’s the nuance most articles skip: knob-and-tube that has been left alone is not inherently a fire hazard. It was a legitimate wiring method, and undisturbed runs have carried power safely for ninety years. The problems are everything that has happened since:

• No ground. Two wires means no ground conductor, so no three-prong outlets, no surge protection that works, and nothing for a fault to trip on.
• Buried in insulation. Knob-and-tube was designed to shed heat into open air. Decades of blown-in attic insulation on top of it changes the math, and this is the condition inspectors flag hardest.
• Amateur splices. Ninety years is a long time for handymen to tap new circuits off old wire. The original work is usually tidy; the 1970s additions rarely are.
• Brittle insulation. The rubber sheathing dries out and cracks where it’s been moved or overheated.

Why your insurer cares more than you do

Most BC insurers now ask about knob-and-tube at renewal or purchase, and many won’t write a standard policy on a house with a meaningful amount of it. Buyers feel this hardest: a financing condition with a 30-day close and a subject-to-inspection report naming knob-and-tube gets stressful fast. If that’s you, an electrician’s written assessment of how much is actually live, versus abandoned in the walls, can settle an insurer’s question and is a much smaller job than a rewire.

It’s the same logic insurers apply to old hazard-brand panels: they’re pricing risk, and undocumented old wiring is a risk they can see. A documented, permitted remediation is usually exactly what turns a “no” into a “yes.”

It usually comes with an old panel

Here’s something that catches people out. A house old enough to have knob-and-tube is often old enough to have a 60-amp service or an aging panel too, and the two problems tend to get solved together. Once you’re opening up the electrical to deal with old wiring, it’s often the right moment to look at whether the service itself needs upsizing, especially if you’re renovating or adding modern loads. That’s a panel or service upgrade, and we’ve written separately about what a panel upgrade actually costs. Bundling the two while the walls are open usually beats doing them as separate jobs a year apart.

What counts as a meaningful amount?

Insurers and electricians both care less about whether any knob-and-tube exists than about how much is still live and where. A few abandoned runs sitting dead in a wall are a different matter from active circuits feeding half the house through insulation. This is why a written assessment is worth so much: it separates the wire that’s actually carrying power from the wire that’s just old and disconnected, and that distinction is often exactly what an insurer needs to see before they’ll write the policy.

How replacement actually works

Full rewires happen, but the more common path is staged: replace what a renovation opens up anyway, then the accessible attic and basement runs, and take the last buried sections when the drywall comes down for other reasons. Any renovation that opens a wall with knob-and-tube in it is required to bring that wiring forward, so the sequencing matters and is worth planning with your contractor before demolition, not during.

Staging it this way spreads the cost and the disruption. It also means you’re not paying to tear open finished walls purely to chase wire, you’re replacing it as the house is opened up for other reasons anyway. A good electrician maps what you have and helps you decide what has to go now and what can wait.

Cost depends on access

Cost depends almost entirely on access, which is why nobody serious quotes a rewire over the phone. A run in an open attic is quick; the same length of wire buried in a finished, insulated wall is a different job. That’s also why the staged approach saves money, it lets the expensive, hard-to-reach sections wait for a renovation that opens them up.

Old homes like this are common right across our service area, from character houses in Vancouver to the older streets of the North Shore and the Fraser Valley. What we can do over the phone is tell you what to look for. A site visit gets you a written fixed price and an honest read on how much of your knob-and-tube is even still connected.