What Derek's Inspector Actually Found
The inspection report noted "knob and tube wiring observed in attic space and accessible areas of second floor." It was flagged as a safety concern with a recommendation for evaluation by a licensed electrician. Pretty standard language.
What made Derek panic was the photos. The inspector had taken close-ups of the ceramic knobs mounted to joists, the tube insulators where wires passed through framing, and the cloth-wrapped conductors running between them. To someone who's never seen it before, it looks ancient. Because it is ancient. This wiring system was standard from about 1880 through the 1940s.
But what you need to know is what the photos didn't show: whether the wiring was actually in bad shape. Knob and tube that's been left alone in open air, not buried under insulation, not modified by amateur electricians, can function safely for decades. The system was actually well-engineered for its time. The wires are spaced apart, which prevents overheating. The ceramic insulators keep conductors away from wood framing.
The Real Problem Isn't Always the Wiring Itself
When the electrician came out, she spent about two hours in Derek's attic. Her name was Pam Whitfield, and she'd been doing residential electrical work in older neighborhoods for 22 years. She told Derek something that changed the whole conversation.
"The knob and tube up here is actually in decent shape," she said. "Your real problem is the blown-in insulation someone added about 15 years ago. It's sitting right on top of the wiring."
Knob and tube wiring was designed to dissipate heat through open air. When someone blows cellulose or fiberglass insulation over it, the wires can't cool properly. That's when fires start. According to the National Electrical Code, knob and tube wiring must not be in contact with insulation. Pam told Derek she sees this exact situation in about a third of the older homes she inspects.
The Insurance Problem Nobody Warned Us About
Derek and Lauren were still processing the electrician's findings when their insurance agent dropped another bomb. Their preferred carrier wouldn't write a homeowners policy on a house with active knob and tube wiring. Period.
This is something I wish more buyers knew before they fall in love with a house. Many insurance companies either refuse to cover homes with knob and tube or require proof that it's been deactivated before they'll issue a policy. Derek called four different insurers. Two said no outright. One said they'd cover it with a 40% surcharge. The fourth said they'd cover it if an electrician certified the wiring was in safe condition and not in contact with insulation.
Lauren told me later she nearly lost it at that point. They'd already spent $650 on the home inspection and $350 on the electrician visit. Now they were being told they might not even be able to insure the place. Organizations like InterNACHI provide standards and training for home inspectors Family Handyman is a good resource for understanding basic home maintenance tasks
What Pam Recommended (and What It Actually Cost)
Pam gave Derek three options, and the price differences were significant.
Option one: full rewire of the entire house. She quoted $16,500 to $19,000 for the bungalow, which was about 1,400 square feet. That would replace every bit of knob and tube with modern Romex wiring, add grounded outlets throughout, and bring everything up to current code. Derek's stomach dropped when he heard that number.
Option two: partial rewire targeting the second floor and attic where the knob and tube was actively being used, plus removal of the insulation touching the wiring. Quote: $6,800 to $8,200. This would deactivate the problematic knob and tube while leaving some inactive remnants in walls that weren't causing issues.
Option three: remove the blown-in insulation from contact with the wiring, repair two splice connections that Pam identified as substandard, and install arc-fault circuit interrupters on the affected circuits. Quote: $2,400 to $3,100. This wouldn't eliminate the knob and tube but would address the actual hazards.
What Derek Negotiated
Armed with Pam's written assessment and quotes, Derek went back to the seller. He asked for a $7,500 credit toward electrical work, pointing to the insulation issue and the insurance complications as justification. The seller countered at $4,000. They settled on $5,500.
Derek went with option two, the partial rewire. With the $5,500 credit, his out-of-pocket cost was about $2,800. Not nothing, but manageable. And his insurance company was satisfied with Pam's certification letter after the work was done.
Here's the part that still bugs me though. If Derek had listened to his agent's initial advice that it was "no big deal," he would have closed without the credit and then discovered the insurance problem on his own. That $5,500 would have come entirely out of his pocket. Getting the electrician's assessment first gave him leverage he wouldn't have had otherwise. This Old House has useful reference material on repair costs and contractor selection
My Cousin's Story Was Different (and More Expensive)
Three years before Derek's situation, my cousin Tara bought a 1922 colonial without getting an electrician to look at the knob and tube her inspector flagged. Her agent told her it was "grandfathered in" and fine. She took that at face value.
Eight months after closing, a small electrical fire started in a second-floor wall. Nobody was hurt, thankfully. But the fire department found that a previous owner had spliced modern 14-gauge wire directly onto the original knob and tube conductors using electrical tape. Not wire nuts. Not proper junction boxes. Electrical tape. The splice had been hidden inside the wall for who knows how long.
Tara's insurance did cover the fire damage, about $14,000 worth. But they then required a full rewire before they'd continue coverage. That cost her $17,200. She told me she cried when she signed the check. "I saved $350 by not getting an electrician before closing," she said. "And it cost me $17,200 eight months later."
I think about Tara's story every time someone tells me knob and tube is automatically fine or automatically terrible. It's neither. It depends entirely on the specific conditions in that specific house. And you can't know those conditions without having someone qualified actually look at it.
What I Tell People Now When They Find Knob and Tube
After watching Derek and Tara go through their respective experiences, I've settled on pretty straightforward advice for anyone whose inspection report mentions knob and tube wiring.
Get an Electrician Before You Decide Anything
Not your uncle who "does electrical work on the side." A licensed residential electrician who has experience with older homes. Ask specifically about their experience with knob and tube. Expect to pay $200 to $400 for a thorough evaluation. That money buys you actual information instead of guesses.
Ask About Insulation Contact
This is the single most important question. Is insulation touching the knob and tube wiring anywhere? If yes, that needs to be addressed regardless of anything else. If the wiring is in open air the way it was designed to be, the risk profile is significantly different.
Call Your Insurance Company Early
Don't wait until closing week to find out your insurer won't cover the house. Call them during your inspection contingency period. If your preferred company won't write the policy, you need time to find one that will or to negotiate repairs with the seller.
Get Written Quotes for Negotiation
Seller negotiations go better with documentation. A written quote from a licensed electrician carries more weight than "the inspector said we need electrical work." Specific numbers lead to specific credits. Derek got $5,500 because he had Pam's detailed assessment showing exactly what needed to happen and what it would cost.
The Bigger Picture on Old Wiring
According to the Electrical Safety Foundation International, electrical fires cause an estimated 51,000 home fires annually in the United States. Outdated wiring is a contributing factor in many of them, though not all involve knob and tube specifically. The reality is that any wiring system, including modern Romex, can be dangerous if it's been improperly modified or maintained.
Knob and tube gets singled out because of its age. And age is a legitimate concern. But the wiring in Derek's attic had been doing its job since Calvin Coolidge was president. The danger wasn't the original installation. It was the blown-in insulation someone added decades later without considering what was underneath it.
If you're buying an older home and the inspection report flags knob and tube, take a breath. It's not an automatic deal-killer. But it's also not something to dismiss. Get it evaluated by someone who knows what they're looking at. That $300 electrician visit might be the best money you spend during the entire home buying process.