Knob and tube wiring is an early type of electrical wiring that carried power through homes built from the early 1900s to the 1940s, using single wires held on ceramic knobs and tubes. Knob and tube isn't illegal in Ontario, and existing wiring can stay in place if it's in good condition, but according to the Electrical Safety Authority (ESA), Ontario's electrical safety regulator, many insurers won't cover or renew a home that still has it. Buyers often get an electrician's assessment and an insurance quote before they firm up an offer.
| When it was used | Early 1900s to the 1940s |
| Allowed in new work today | No. Installation rules were removed from the Ontario Electrical Safety Code in 2021 |
| Can existing wiring stay? | Yes, if it meets ESA's conditions (below) |
| Who assesses it | A Licensed Electrical Contractor |
| Main problem for buyers | Getting home insurance |
How to spot knob and tube wiring
Knob and tube is easiest to see where the framing is exposed: an unfinished basement ceiling or the attic. Look for single wires running separately, a few inches apart, held off the wood by white ceramic knobs, and passing through joists inside ceramic tubes. The wires usually have a cloth or rubber covering rather than modern plastic sheathing. ESA now calls it "open wiring".
Other clues inside the house:
- Two-prong outlets with no ground hole, especially in original rooms.
- A fuse panel, or 15 amp fuses or breakers feeding old circuits.
- An older house that has only been partly updated. Many homes built before 1950 have been fully rewired, and many have a mix: a new panel and new kitchen circuits, with some original wiring still live in the walls upstairs.
You often can't see it at all. Most of it runs inside finished walls and ceilings, so a home inspector may note that the house is "likely" to have some, or find one live run in the basement and be unable to say how much more there is. Only an electrician who tests the circuits can tell you how much is still in use.
Why insurers care
Many insurers treat knob and tube as a higher risk. ESA's own notice says that many insurers will not provide or renew coverage on homes with this wiring, and that in some cases insurers require a total replacement before they'll insure the home.
Insurer stances vary. Some won't quote at all; some will insure the home if a Licensed Electrical Contractor (a business licensed in Ontario to do electrical work for hire) inspects it and confirms it's in good condition; some will insure it for a set period while you replace it; and some charge a higher premium. The questions are usually:
- Is any knob and tube still live (connected and carrying power), or has it all been disconnected?
- How much of the house is still on it?
- Do you have a letter from an electrician, or an ESA certificate, showing what's been done?
Because the answer depends on the insurer, call yours, or a broker, with the inspection report in hand before you count on coverage. Your lender needs proof of home insurance before closing, so this isn't something to discover in the last week.
Is knob and tube wiring dangerous?
Knob and tube wiring is not automatically dangerous. According to the Electrical Safety Authority, knob and tube is safe provided it's properly maintained by a Licensed Electrical Contractor, and that original wiring in good condition that hasn't been altered won't present undue hazards. The Ontario Electrical Safety Code isn't retroactive, so wiring that was legal when installed isn't in violation just because the rules changed.
ESA says existing knob and tube can stay in place if all of these are true:
- It's protected by a 15 amp fuse or circuit breaker.
- No outlets have been added to the original circuits in a way that overloads them.
- The wires, where you can see them, appear to be in good condition.
The real risks come from age and from what owners have done to it over the decades. ESA says it should be replaced where the wires show physical damage or deterioration, poor connections, signs of overheating, or changes that overload the circuit or break the Code. The unsafe practices it lists in older homes:
- Oversized fuses, such as a 20 or 30 amp fuse put in where a 15 amp one belongs.
- Extension cords used as permanent wiring, because the house has too few outlets.
- Outlets added or connections made to the old wiring by someone who wasn't a licensed contractor.
- Three-prong outlets swapped in without a ground. ESA allows a three-prong outlet on an ungrounded circuit only if it's protected by a ground fault circuit interrupter (GFCI), a device that cuts power when current leaks to ground.
Knob and tube also has no ground wire, and older homes usually have fewer circuits and less capacity than a modern household uses. A Licensed Electrical Contractor can check the wiring for all of this. ESA notes that this is different from a home inspection, which looks at the whole house and doesn't test the electrical in depth.
Replacement cost and how long it takes
There's no reliable standard price for replacing knob and tube. The cost depends on how much of the house is still on it, the size and layout of the house, how many floors there are, and how easy it is to run new wire through finished walls and ceilings, especially plaster. Get written quotes from two or three Licensed Electrical Contractors for the specific house.
What usually drives the price:
- How much is still live. Removing a few remaining circuits is a much smaller job than rewiring a whole house.
- Access. An unfinished basement and an open attic make the work easier. Finished basements and plaster walls mean more openings.
- Wall and ceiling repair. Electricians cut access holes. Patching and painting afterwards is often a separate cost, with a separate trade.
- Upgrades that come with it. A rewire is often paired with a new panel or a bigger electrical service, and new circuits have to meet today's Code, including GFCI protection in bathrooms, outdoors and near kitchen sinks.
How long it takes depends on the same things, so ask the electrician for a timeline with the quote. Some people do it before they move in, while the house is empty, which is usually easier for the electrician.
Any rewiring has to go through ESA. The contractor files a notification of work with ESA and the work is inspected. When it passes, ESA issues a Certificate of Acceptance. Keep it: ESA describes it as an important document for insurance and resale, and it's what an insurer may ask to see.
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Buying a home that has knob and tube
The key with a house that has knob and tube is to find out what you're dealing with before your offer is firm, while you can still walk away. Talk to your agent and lawyer about how to word the conditions for your situation.
Conditions buyers commonly use
- A home inspection condition. This gives you time for a general inspection, and to bring in an electrician if the inspector flags anything.
- An insurance condition. This makes the deal depend on your getting home insurance you're satisfied with. With knob and tube, it gives you a way out if no insurer will cover the house on terms you can live with.
- A financing condition. Your lender needs proof of insurance, so the two are linked.
In a competitive market, buyers sometimes make offers with no conditions. With an older house, that means doing the insurance and electrical homework before you make the offer.
Get an insurance quote first
Call an insurer or broker with the address, the year built, and whatever the listing or a pre-list inspection says about the wiring. Ask whether they'll cover it as-is, what they need to see (an electrician's letter, a certificate, a replacement deadline), and what it does to the premium. Getting these answers from more than one insurer tells you how much of a problem it really is for this house.
Get an electrician's assessment
A Licensed Electrical Contractor can tell you how much knob and tube is live, what condition it's in, and what it would take to remove it, with a written quote. That quote is the number to weigh against the price.
Check ESA's records
ESA suggests buyers request a Search of Records from ESA before a sale is final. It shows any open notifications on the property since 2000, meaning electrical work that was filed but never inspected and closed. If the seller says the house was rewired, the records and a Certificate of Acceptance are how you confirm it.
If the seller says it's been removed
Ask for the paperwork: the Certificate of Acceptance, the electrician's invoice, or a letter describing what was replaced. "Mostly rewired" is common in older homes, and the circuits that weren't done are the ones an insurer will ask about.
Where older homes are in Waterloo Region
Knob and tube is only found in houses built while it was in use, so it's most likely in the region's oldest neighbourhoods: the original cores of Kitchener, Waterloo and the Cambridge communities of Galt, Preston and Hespeler, plus older village centres in the townships. Here's a table of the neighbourhoods where the highest share of recent sales were homes built before 1950, among sales with a known build year, each linked to its neighbourhood page.
| Neighbourhood | City | Share built before 1950 | Sales with a known build year |
|---|---|---|---|
| Victoria Park | Kitchener | 92% | 135 |
| MacGregor Albert | Waterloo | 76% | 51 |
| King East | Kitchener | 72% | 154 |
| Central Frederick | Kitchener | 63% | 320 |
| Northward | Kitchener | 63% | 82 |
| Auditorium | Kitchener | 57% | 244 |
| Midtown | Kitchener | 56% | 222 |
| Lincoln Oaks | Cambridge | 56% | 418 |
| Downtown Hespeler | Cambridge | 52% | 159 |
| Riverview | Cambridge | 44% | 353 |
| Civic Centre | Kitchener | 44% | 154 |
| Mt. Hope Huron Park | Kitchener | 43% | 556 |
The neighbourhoods with the highest share of sales of homes built before 1950, among sales with a recorded build year, over the 10 years ending October 26, 2026. Neighbourhoods with fewer than 30 such sales aren't shown. Build years come from listings and aren't always recorded.
A pre-1950 build year doesn't mean a home has knob and tube, and a later one doesn't rule it out; only an inspection tells you.
See more on each city's market: Kitchener, Waterloo, Cambridge, Woolwich, Wilmot, Wellesley and North Dumfries.
Knob and tube is one of several things that can turn up when you're buying an older house. For the rest of the process, see the first-time home buyer guide, and budget for the closing costs that come on top of the price.