By Christopher B. Smith — Red Seal Carpenter and BCIN-licensed designer, Woodsmith Construction. East Toronto.
The basement was the reassuring part.
New panel on the wall. Breakers, not fuses. Neat runs of modern cable stapled along the joists, all of it tidy, all of it obviously done in the last twenty years. If you were standing there deciding whether to buy the house — or deciding whether the renovation you have in mind is going to be simple — you would look at that panel and tick the box. Electrical: done.
We are in that house right now — a project in the East End, a renovation that was scoped and priced like any other. The panel was telling the truth about the basement and nothing else. Above the finished ceilings on the floors overhead, the original knob-and-tube was still live, still carrying load, and in worse condition than anything our electrician had seen in a long time.
This is the most common misunderstanding we run into on older east-end houses, and it is worth explaining properly — because knob-and-tube changes a renovation, but not always in the direction people assume, and not always as much as they fear.
What knob-and-tube actually is
It is the wiring method used in houses built roughly between the 1900s and the 1940s — which is most of Riverdale, Leslieville, the Danforth and a good part of East York and the Beaches.
Two separate conductors, a hot and a neutral, run independently through the building rather than bundled together in a single cable. Where they pass through a joist or a stud they run inside a ceramic tube. Where they run along a surface they are held off it by a ceramic knob. That air gap is the entire design: the wire was meant to sit in open air, spaced away from wood, shedding its heat as it goes.
Two things follow from that, and they matter later. There is no ground conductor — which is why you find two-pin outlets in these houses. And the system depends on air around the wire.
Why a new panel does not mean new wiring
Here is the part that catches people.
Replacing a panel and replacing the wiring are two completely different jobs. A panel swap happens in one location, in a day, and it is visible. Rewiring a house means getting a new conductor to every outlet, switch and fixture in the building — through finished plaster walls, around solid blocking, in a house with no stud cavities to speak of and no chases. It is disruptive, it is expensive, and it is invisible when it is finished.
So a very common history in these houses is: the service got upgraded at some point, the basement got redone because the basement was open, a few circuits got extended, and everything above the first-floor ceiling was left exactly as it was and covered back up.
From the basement, that reads as a modernised house. From inside the ceiling, it is not.
There is a second version of this that is harder to spot, and we hit it in this house. Somebody had already been in there. The knob-and-tube had been worked on — spliced, re-routed, joined into newer wire, with a junction box sitting beside a light fixture. It had been redone rather than replaced. Honestly, more trouble had been taken doing it that way than it would have taken to do it properly.
That is the thing a new panel cannot tell you.
The tell most people miss: look for damage that is not there
Here is the check we actually use, and it costs nothing.
In a plaster house, you cannot get a new wire from a switch up to a ceiling light without opening something. There is no cavity to fish through, there is solid blocking in the way, and the lath and plaster will not cooperate. To rewire that switch loop somebody has to cut the wall, or cut the ceiling, or both — and then patch it.
So look for the patch. Stand in a room and look at the wall above each light switch, and at the ceiling around each fixture, in raking light from a window. Plaster repair almost always shows: a slightly different texture, a flatter or shinier patch, a hairline seam, a section that reads subtly proud of the surrounding surface. Look on the second floor especially, and on the first.
If you cannot find that evidence anywhere — no patches above the switches, no repairs around the ceiling boxes, original plaster running clean and unbroken — then in all likelihood nobody ever got a new wire up there. The lighting circuits are probably still the originals.
It is a strange thing to go looking for the absence of damage as a warning sign. But in a house of this age, undisturbed plaster over a switch is not a sign of good condition. It is a sign that nothing has been done.
What we found once the ceiling came down
The sequence in this house is worth laying out, because it is the ordinary sequence, not a horror story.
Late July — exploratory demo. Before anything else, the rule on site for old wiring is simple and it does not change: breaker off, line tested, breaker taped. Nothing gets disconnected, extended or hooked up without a licensed electrician. We are carpenters; we open things up and we stop.
Early August — confirmation. With sections open, the knob-and-tube was confirmed live and widespread, heaviest on the third floor. That is typical. The top floor is the furthest from the panel and the least likely to have been touched during any previous partial renovation.
Late August — the ceiling. When the main ceiling came down we found the rest of it: old ungrounded wiring with no neutral, load split from an uninsulated run into an insulated one, live wires cut off and left, and heavy rodent damage through the whole assembly. Our electrician called it a fire hazard and one of the worst he had seen.
That ceiling was not in the original scope. It came down because of what we found behind it, and once it was down the work above it grew. This is the honest version of unexpected costs — not a surprise anyone invented, just a house telling you what it actually is once you can see it.
Two things worth saying alongside that, because the picture is not all bad. The joists in that ceiling were in excellent condition after more than a century — an unsealed house that can breathe, expand and dry out ages far better than a tightly sealed one, and there was no moisture problem anywhere. And it is genuinely a good thing the ceiling came down. What was above it was going to sit there indefinitely otherwise.
What the rules actually say — and do not
This is where most of what homeowners have been told falls apart.
Knob-and-tube is not illegal, and you are not required to remove it. The Electrical Safety Authority says so plainly. Its current notice on the subject states that knob-and-tube wiring “is safe, provided it is properly maintained by a Licensed Electrical Contractor.”
What changed is that you can no longer install it. The installation rules were deleted from the 28th Edition (2021) of the Ontario Electrical Safety Code. But — in the ESA’s own words — “the OESC is not retroactive.” Existing knob-and-tube is permitted to remain in place where:
- it is protected by a 15 A fuse or breaker;
- no additional outlets have been added to the original circuit in a way that overloads it; and
- the conductors, where visible, appear to be in good condition.
Read those three conditions again, because the failure mode is in the second one. Knob-and-tube in its original state, properly fused and untouched, is not the problem. The problem is a hundred years of people adding to it. The most serious risk in these systems is almost always the unpermitted work that was done to them, not the original wiring itself.
Which is exactly what we found. The wire was not the villain. What had been done to it was.
The question nobody answers: what does touching it drag in?
If you are planning a renovation, this is the question that actually decides your budget, and it has a specific answer.
The ESA’s guidance on replacements and alterations in dwelling units sets out what gets triggered:
- Replace the branch-circuit wiring to existing receptacles, and that circuit now needs arc-fault protection, and those receptacles have to be replaced with grounded three-pin, tamper-resistant types.
- Extend an existing circuit by adding a receptacle, and arc-fault protection is required at the first added receptacle.
- But upgrade the panel or the service on its own, adding no receptacles, and arc-fault protection is not applied retroactively to the existing branch circuits.
That last point is the one that saves people money and almost nobody knows it. A service upgrade does not, by itself, oblige you to rewire the house.
And in a smaller renovation, the new requirements attach to the new circuits. Touching one room does not automatically drag the whole building into scope. It is also the hinge on which a basement suite turns, because subdividing a dwelling unit brings its own electrical requirements with it.
This is the difference between a renovation that grows sensibly and one that grows uncontrollably, and it is worth having your designer and your electrician answer it before the drawings are finished rather than after the walls are open. It belongs in the same early conversation as the permit process.
When you need an ESA notification — and when you do not
Also more nuanced than the internet suggests.
A full or partial rewire is notifiable work and needs a licensed electrical contractor. That is not in question.
But a licensed electrical contractor replacing receptacles or general-use switches on knob-and-tube in an owner-occupied home — including swapping in GFCI receptacles on an ungrounded circuit — does not require a notification to be filed.
The reverse is the part homeowners get wrong: you may not do that yourself. The do-it-yourself exemption that lets a homeowner change a light fixture specifically excludes knob-and-tube and other ungrounded wiring. And the whole exemption applies only to owner-occupied homes — not rentals.
There is also a legitimate middle path that gets very little airtime. On an ungrounded circuit, GFCI protection can provide ground-fault protection without rewiring. It is not the answer everywhere and it does not turn an ungrounded circuit into a grounded one. But it exists, it is code-compliant, and it is worth asking your electrician about. We mention it because we are not the ones selling you the rewire.
The insurance problem, stated accurately
This is usually what forces the issue, and it is worth being precise.
The ESA’s own wording is that many insurers will not provide or renew coverage on homes with this type of wiring, and that some will require it to be replaced before they will write a policy.
That is not the same as “no one will insure you.” At least one Ontario-licensed provider openly advertises coverage for homes with knob-and-tube. Others will write the policy subject to an electrical inspection or a remediation timeline.
You will find a lot of confident percentages online about how many insurers refuse and how much they surcharge. We are not going to repeat any of them, because the numbers we found contradicted each other and none traced back to a source worth citing. Call your broker and ask about your house. That is the only number that matters.
The insulation question
Insulating over old wiring comes up constantly, usually as somebody’s half-remembered version of a rule. It is worth being clear about what kind of question it is.
It is an electrical question, not an insulation question. The wiring rules are what govern here, and the person who gets to answer is a licensed electrical contractor — not the insulation installer, not the home inspector, and not us. Start from the fact that this wiring method is no longer permitted to be installed at all, and you have the right instinct about how it should be treated when you start burying it in a wall or an attic.
The physical reason is straightforward. Knob-and-tube was designed around an air gap — conductors held off the framing, running in open air, shedding heat as they go. Pack insulation tight around them and you have removed the mechanism the whole design depends on. That is a real concern, it is why insurers ask about it, and it is why the answer is an electrician’s assessment before anybody insulates rather than a rule of thumb off the internet.
And there is a practical trap attached to it right now. Ontario’s home-renovation rebate programme includes an attic-insulation stream, which is doing exactly what you would expect: encouraging people to blow insulation into the attics of old houses. Two cautions if that is on your list. First, the wiring in that attic should be assessed before anybody insulates over it. Second — and this catches people — that programme requires the work to be done by one of its own approved installers, and work that starts before their site visit does not qualify. If you are also renovating, opening that roof or attic yourself first can cost you the rebate. Sequence it deliberately, and check what you can actually claim before anyone starts.
How this should change the renovation you are planning
Here is the part that competitors, insurers and electricians all miss, because none of them is standing in the middle of a renovation.
If the walls and ceilings are already coming down, the rewire gets dramatically cheaper.
Almost the entire cost of a standalone rewire in a finished house is access — cutting into plaster, fishing wire through blocking, then patching, sanding and repainting every wall you opened. Do it while the house is already open for other reasons and that whole category of cost largely disappears. You are paying for wire, devices and labour, not for the destruction and reconstruction of finished surfaces.
Which leads to the single worst version of this: rewiring a finished house as a standalone project, and then gutting it eighteen months later. We see it. It is a genuinely avoidable waste, and it is the same mistake as every other one in the order you do things in — doing the visible work before the structural work.
So, practically:
- If you are renovating anyway, and knob-and-tube is present and live, deal with it in the same pass. It will never be cheaper than when the walls are open.
- If you are not renovating, you are not obliged to rewire. Get a licensed electrician to assess it, sort out the fusing and any past butchery, and make a plan.
- If you are phasing over years, get the wiring done in whichever phase opens the most of the house — and make sure the electrician knows about the phases that are coming, so the work is sized for the house you will end up with.
- If you are still deciding whether to buy, look at the panel, then look past it. Ask what is above the first-floor ceiling.
It is one more line in the same ledger as everything else that makes an older east-end house cost what it costs, and it behaves the same way: cheap to deal with while you are already in there, expensive to deal with on its own.
Woodsmith Insight: The house we are in now went from a scoped renovation to a materially bigger one because of what was over a ceiling nobody had planned to remove. Nothing about that was avoidable — it was already there, it had been there for decades, and it was going to stay there until someone opened it up. What is avoidable is finding it in month three instead of at the design stage. On a house of this age, budget for the possibility that the wiring above your finished ceilings is not what the basement suggests. If we are wrong, you have contingency left over. If we are right, you have a plan instead of a problem.
Before you buy, or before you start
Seven things worth doing, none of which require a contractor:
- Look at the panel — then discount it. A modern panel says nothing about what is above the first-floor ceiling.
- Look for plaster repair above the light switches and around the ceiling fixtures. In raking light, on the first and second floors. You cannot rewire a switch loop in a plaster house without cutting and patching — so if there is no patch anywhere, the lighting circuits were probably never touched. This is the best free check on the list.
- Count the two-pin outlets. Ungrounded outlets upstairs, especially on the top floor, are the clearest free clue you will get.
- Look at the fuse or breaker sizes on any old circuits. Anything over 15 A on original wiring is a question that needs an answer.
- Get into the attic and the basement and look at what leaves the panel. Cloth-sheathed conductors and ceramic knobs are unmistakable once you have seen them.
- Ask the seller what was rewired and when — and ask whether there is an ESA certificate for it.
- Call your insurance broker before you firm up an offer, not after.
None of that is a diagnosis. It narrows the range; it does not close it. But it tells you whether you are buying a house with a wiring question attached, which is worth knowing before you write the offer rather than after — and it sits alongside everything else that shapes what a century home costs to renovate.
One note on a close cousin: houses built roughly between the mid-1960s and the late 1970s — a lot of the post-war stock further north and east — often have aluminum branch wiring instead. Different material, different remediation, similar insurance friction. That is its own subject and we will cover it separately.
If you are looking at an older east-end house and trying to work out whether the wiring is a footnote or a chapter, talk to us. We will tell you honestly which one it is — and if the answer is that you do not need to do anything yet, we will tell you that too.
Frequently asked questions
No. It can no longer be installed — the installation rules were removed from the 28th Edition (2021) of the Ontario Electrical Safety Code — but the Code is not retroactive, and the Electrical Safety Authority permits existing knob-and-tube to remain where it is protected by a 15 A fuse or breaker, has not had outlets added in a way that overloads the circuit, and appears to be in good condition where visible.
Not inherently. The ESA’s position is that it is safe when properly maintained by a licensed electrical contractor. The risk in practice comes from what has been done to it over the decades — overfusing, unpermitted additions, splices into newer wire, and damage — rather than from the original installation.
Look for plaster repair above the light switches and around the ceiling fixtures, in raking light, on the first and second floors. In a plaster house you cannot get a new wire from a switch up to a ceiling light without cutting something open and patching it afterwards. If there is no sign of that repair work anywhere in the house, the lighting circuits have most likely never been replaced. It is not proof, but it is the most useful thing you can check for free.
No, and this is the most common misunderstanding we see. Replacing a panel is a one-location job; rewiring a house means reaching every device in the building through finished walls. It is very common for the service and the basement to have been modernised while everything above the first-floor ceiling was left untouched.
Generally no. The new requirements attach to the work you are doing. Replacing the branch-circuit wiring to existing receptacles brings arc-fault protection and grounded, tamper-resistant receptacles into play for that circuit, and extending a circuit triggers arc-fault protection at the first added receptacle — but a small renovation does not automatically pull the untouched parts of the house into scope.
No. Where the service or panel is replaced, relocated or upgraded and no receptacles are added, arc-fault protection is not applied retroactively to the existing branch circuits. A service upgrade on its own does not oblige you to rewire.
Often, but not always straightforwardly. The ESA notes that many insurers will not provide or renew coverage on homes with this wiring, and some require replacement first. Others will write a policy subject to an inspection or a remediation timeline. It varies enough by insurer that the only reliable answer comes from your own broker.
No. The do-it-yourself exemption that normally lets a homeowner swap a fixture or switch specifically excludes knob-and-tube and other ungrounded wiring. A licensed electrical contractor can do that work in an owner-occupied home without filing a notification, but a homeowner cannot do it themselves.
Substantially, yes. Most of the cost of rewiring a finished house is access — opening finished walls and ceilings and then patching, sanding and repainting them. If those surfaces are already coming down for other reasons, that cost largely disappears. Rewiring a finished house and then gutting it a year later is one of the more expensive sequencing mistakes we see.
Treat it as an electrical question and have a licensed electrical contractor assess it before anyone insulates. Knob-and-tube was designed around an air gap and sheds its heat into open air; burying it in insulation removes that. It is also worth checking the rules of any rebate programme before work starts — Ontario’s attic-insulation stream requires an approved installer and a site visit before work begins, so opening things up yourself first can disqualify you.
