Like horsehair plaster, finding it shouldn’t automatically send you into a panic. But unlike plaster, this is part of the electrical system.
If you’re remodeling an older house in Central Pennsylvania, there’s another thing we sometimes find once the walls come open: knob-and-tube wiring.
When we find it, we need to figure out exactly what is still active, what condition it’s in, and how it affects the work we’re about to do.
Knob-and-tube was an early method of residential electrical wiring. Instead of the hot and neutral conductors being bundled together inside one cable like modern wiring, they were run separately through the framing.
Porcelain knobs supported the wires as they ran along framing.
Porcelain tubes protected them where they passed through wood.
Hence the name.
If you own a house from the late 1800s or early 1900s, finding some isn’t particularly unusual. The bigger question is whether it’s still being used.
Old houses tend to accumulate generations of work. Maybe most of the electrical system was updated 30 years ago, but one second-floor lighting circuit wasn’t. Maybe a previous renovation replaced everything that was easy to reach and left wiring inside walls untouched. Maybe somebody installed modern receptacles and switches while portions of the older system remained behind them.
A house can look completely modern at the electrical panel and still have older wiring buried somewhere in the walls.
That’s why we don’t guess. If we find knob-and-tube during a remodel, an electrician needs to determine what’s active and what it’s serving.
Knob-and-tube was a legitimate wiring method in its time. But we’re talking about wiring that may now be around a century old, and a lot can happen in 100 years.
And somebody’s uncle may have “fixed” something in 1974 that nobody has looked at since.
The fact that the wiring is old matters. What has happened to it during the last century matters even more.
There’s a big difference between buying an old house that happens to contain some knob-and-tube and opening the walls in that house for a major renovation. Once we’re remodeling, we’re disturbing things.
Maybe we’re adding outlets.
Maybe we’re moving switches.
Maybe we’re installing recessed lighting.
Maybe we’re building a new bathroom or kitchen with completely different electrical requirements.
Maybe we’re opening walls that haven’t been touched in 80 years.
At that point the existing electrical system becomes part of the project. We can’t build new work around an old condition without first figuring out what we’re dealing with.
Sometimes old knob-and-tube is already abandoned. That’s different. If it’s disconnected and no longer part of the electrical system, finding the old porcelain knobs or wires inside a wall can simply be evidence of how the house used to be wired.
Active wiring is another matter. Whether existing knob-and-tube can remain depends on its condition, the work being performed and applicable electrical requirements. That’s an electrician-and-inspector conversation, not something I’d want to make a blanket rule about from looking at one wire sticking through a joist.
And if the walls are already open and the circuit can reasonably be replaced, that’s usually the time to have the conversation. Closing everything back up around a questionable old circuit just because it still technically works can be a pretty short-sighted way to save money.
This becomes particularly important when an older house is being insulated. Knob-and-tube was designed differently from modern cable assemblies, including how the conductors dissipate heat. That means you shouldn’t simply bury active knob-and-tube in new insulation without determining whether the proposed assembly is permitted and appropriate.
This comes up during whole-house renovations, exterior wall work and energy upgrades. You start with “we’re going to insulate these walls while they’re open.” Then we discover active knob-and-tube. Now the electrical work may need to happen before the insulation.
That’s exactly why older-house remodeling needs to be planned as a system instead of treating framing, electrical, plumbing and insulation as unrelated jobs.
Modern kitchens use a lot of electricity. So do modern bathrooms. Think about what we’ve added to houses over the years — microwaves, dishwashers, garbage disposals, hair dryers, heated bathroom floors, ventilation fans, more lighting, more receptacles, larger appliances.
Knob-and-tube came from a completely different era of residential electrical demand.
So if we’re gutting an old kitchen or bathroom, we’re not simply asking whether the old wiring currently turns a light on. We’re asking whether the electrical system we’re leaving behind makes sense for the new room we’re building.
Say we’re remodeling a bathroom in a 100-year-old house. We know it’s an old house. We know there’s a possibility of old wiring. That’s something we should be thinking about before demolition.
Then we open the walls. We discover that the bathroom lighting is still being supplied by active knob-and-tube, and the same circuit continues upstairs into areas we’re not remodeling.
Now we need to figure out where it goes.
What does it feed?
Where can we access it?
How much needs to be replaced?
Can we isolate the affected portion without tearing apart half the house?
Those answers can affect the project. And sometimes we genuinely can’t know them until the wall is open.
This is the same distinction I make when talking about change orders and contingencies. If you’re estimating a major remodel in a 120-year-old house, you should expect some old-house problems.
That doesn’t mean the contractor can know exactly what’s inside every wall. But it does mean the contractor should recognize the risk. If there are visible signs of an older electrical system before construction, that should be investigated as far as reasonably possible.
If the entire project depends on the assumption that every wire behind the wall will be brand new, despite everything else in the house being 100 years old, that’s not much of a plan.
Good pre-project planning doesn’t eliminate every surprise. It separates the things we should have anticipated from the things nobody could reasonably see.
This one is worth saying separately. A newer breaker panel is a good thing. It does not necessarily tell you the age of every wire in the house.
Electrical systems are often updated in stages. Someone may have replaced the service and panel years ago without rewiring every circuit. Then another owner renovated the kitchen. Someone else added a bathroom. Another person finished the basement. Now you’ve got several generations of electrical work all connected to the same panel.
That’s why older homes need to be evaluated based on what’s actually there, not just how new the panel cover looks.
First, don’t panic.
Second, don’t cover it back up and pretend we didn’t see it.
We determine whether it’s active. Then a qualified electrician evaluates the condition, where it goes and how it interacts with the work we’re doing. From there we can make an informed decision about what needs to happen.
On a smaller project, that might mean dealing with one affected circuit. On a major renovation with walls already open, it may make sense to replace considerably more. The right answer depends on the house.
Not automatically. This is where remodeling projects can get out of control if nobody stops to think. You open one bathroom wall, find old wiring, and suddenly somebody wants to turn a bathroom renovation into a whole-house rewire.
Maybe that’s justified. Maybe it isn’t. I’d want to know how much knob-and-tube remains, its condition, how accessible it is, what else has already been updated and how much of the house we’re opening anyway.
If we’re already doing a full gut renovation, the math can change dramatically because access is there. If we’re remodeling one small room and the rest of the house is finished, that’s a different situation.
Do the work that makes sense for the house and the project.
Knob-and-tube is a perfect example of something that can create legitimate uncertainty. Maybe we know some old wiring exists but can’t determine exactly where it goes without opening finished walls. We can account for that risk in the budget. That’s what a construction contingency is supposed to do.
It’s different from pretending the risk doesn’t exist, submitting the lowest estimate and then handing the homeowner a giant change order after demolition.
There are things we can know before construction.
There are things experience tells us are likely.
And then there are things the house simply won’t show us until we open it.
A good estimate needs to understand the difference.
What a contingency is, and what it isn’t →
We work in an area with a lot of old homes. And I like old houses. Many have framing, masonry, trim and craftsmanship that would cost a fortune to reproduce today.
But owning and remodeling one means accepting that different generations of building materials and systems may be hiding behind the finished surfaces. Horsehair plaster is one. Old plumbing is another. Knob-and-tube wiring is another. None of those automatically mean the house needs to be gutted. They mean you need to understand what you’re working with.
If we find knob-and-tube during a renovation, our job isn’t to scare you. It’s to figure out what’s active, determine what actually needs to be addressed, and make sure the new work we’re putting back makes sense with the house around it.
That’s how an old house should be remodeled.
Understand what’s there first. Then decide what actually needs to change.
On the Sunbury bathroom the walls came open on a house old enough to have it. Our electrician took the knob-and-tube out entirely and replaced it with Romex run straight from the panel — while the access was already there.
Fifteen minutes on the phone. You’ll have a realistic range before we hang up — and if we’re not the right people for it, I’ll tell you.