Knob-and-Tube Wiring on a Home Inspection
Knob-and-tube is the original wiring in a lot of pre-1940s houses. The wire itself was often installed well. The trouble is a century of age, insulation piled on top, and later add-ons, plus insurers who don't want it. Find out what's still live and whether you can insure the house before your deadline.
I'm Wes Johnston, a Realtor with Trueblood Real Estate in Fishers. Before real estate I earned a construction engineering management degree from Purdue and spent about ten years designing custom homes and running their construction in Hamilton County. I'm not a home inspector, electrician, plumber or engineer, and this isn't a substitute for one. It's how I explain these findings to my own clients. Sources are linked as you go.
Short answer: live knob-and-tube usually means planning a rewire of those circuits, and the insurance question often decides the timing. Abandoned, disconnected knob-and-tube is a much smaller item. Have a licensed electrician confirm what's active and quote the work, and call your insurer, before the inspection deadline.
- Typical cost to fix
- Whole-house rewire about $6 to $10 per sq. ft., or $12,000 to $20,000. Partial rewires and abandoned wiring cost less; get a quote.
- Who to call
- A licensed electrician. Your insurance agent, the day the report arrives.
- Deal-breaker?
- Sometimes. Usually it's a price and insurance negotiation. It can end a deal if you can't get coverage.
Cost source: HomeAdvisor electrical panel and rewiring cost guide, updated June 17, 2026, national figures
- 01What is knob-and-tube wiring and how do I recognize it?
- 02Is knob-and-tube wiring dangerous?
- 03Why does insulation over knob-and-tube wiring matter?
- 04Does knob-and-tube wiring have to be replaced?
- 05Can you get homeowners insurance with knob-and-tube wiring?
- 06How much does it cost to replace knob-and-tube wiring?
- 07Should I ask the seller to replace knob-and-tube wiring?
- 08Should I buy a house with knob-and-tube wiring?
- 09I'm selling a house with knob-and-tube. What should I do before listing?
What is knob-and-tube wiring and how do I recognize it?
Knob-and-tube was the standard way to wire a house in North America from about 1880 into the 1940s. Separate insulated copper wires, one hot and one neutral, run through porcelain tubes where they pass through drilled framing and along porcelain knobs nailed to the framing. Where the wires enter a box or a wall, they're covered in a cloth or rubber sleeve called loom (InterNACHI).
You'll usually spot it in an unfinished basement or the attic: two wires running a few inches apart on white porcelain knobs. One caution from a Minnesota inspection firm: a single wire strung between ceramic knobs in an attic may be an old radio antenna, not wiring (Structure Tech).
In central Indiana, this shows up in pre-1940 Indianapolis bungalows and four-squares, older homes in the historic neighborhoods, and the original cores of the small towns around the city, often mixed with later wiring. Typical report wording: "Knob-and-tube wiring observed in attic/basement. Unable to determine extent or whether active. Recommend evaluation by a licensed electrician."
Is knob-and-tube wiring dangerous?
Less than its reputation, more than you'd want to ignore. InterNACHI calls it obsolete and a potential hazard, "although some of the fear associated with it is undeserved" (InterNACHI). Structure Tech puts it more bluntly: "There is nothing inherently unsafe about knob and tube wiring," but "in nearly every home that we inspect with knob and tube wiring, we find unsafe alterations that need repair" (Structure Tech).
The original system had real strengths. With the wires separated in open air, it sheds heat well, and the porcelain lasts a very long time (InterNACHI). What goes wrong:
- No ground wire, so it can't properly serve three-prong appliances. Many of these houses have three-prong outlets that aren't actually grounded, or are grounded to a water pipe that later got replaced with plastic (Structure Tech). See the ungrounded outlets page.
- Aging insulation that turns brittle, cracks when bent, or breaks down from heat, most often in hot attics, leaving bare conductors (InterNACHI; Structure Tech).
- Amateur splices and add-ons, including connections to modern wire without a junction box and tape that isn't electrical tape (InterNACHI).
- Overloading. It was built for a much smaller electrical load. InterNACHI notes owners sometimes installed fuses too large for the wire, which leads to heat damage (InterNACHI).
- Wet locations. InterNACHI advises against using it in kitchens, bathrooms, laundry rooms or outdoors, because many types of its insulation aren't rated for moisture (InterNACHI).
Why does insulation over knob-and-tube wiring matter?
Because the system was designed to cool itself in open air. InterNACHI says insulation around knob-and-tube wires causes heat to build up and creates a fire hazard, and that the 2008 National Electrical Code prohibits covering it with insulation, though local codes vary (InterNACHI).
Structure Tech adds a second heat problem: modern light fixtures call for 90°C-rated wire, while knob-and-tube is rated for 60°C, so connecting a new fixture straight to it without a transition box can overheat the old insulation until it flakes off (Structure Tech).
This is the combination I look for in older houses. Someone upgrades the attic insulation to save on heating, blows it in deep, and buries live knob-and-tube that was fine in open air for generations. On a report, "knob-and-tube observed in attic" plus "insulation depth adequate" is a combination I ask the electrician about specifically.
The fix is usually to rewire those attic and exterior wall runs before anyone adds insulation. If you're buying an older house with plans to insulate it, put the electrician first in line.
Does knob-and-tube wiring have to be replaced?
Not by any blanket rule. InterNACHI says no code requires complete removal; some places require removal at accessible locations and others only require an inspection. Its advice is to replace wiring that's brittle or cracked (InterNACHI). In practice, the insurance question tends to drive the decision more than code does.
The first question is whether it's live. Abandoned, disconnected knob-and-tube in the attic is a very different finding from active circuits feeding bedrooms. An electrician can tell you which runs are energized and what's tied into them. Get that in writing; it changes everything downstream.
| What the electrician finds | Usual path |
|---|---|
| All abandoned and disconnected | Written confirmation it's dead; maybe remove what's accessible |
| A few active circuits | Replace those circuits |
| Active throughout | Plan a rewire, often with a panel upgrade |
| Buried in insulation or damaged | Prioritize those runs before anything else |
Can you get homeowners insurance with knob-and-tube wiring?
It can be hard. InterNACHI says many insurers refuse to cover homes with knob-and-tube because of fire risk, with some exceptions when an electrical contractor certifies the system as safe (InterNACHI).
The most specific data I found is a July 2019 survey by Structure Tech, a Minnesota inspection firm, which asked 30 insurers whether they'd insure a home with knob-and-tube (Structure Tech):
| Answer | Insurers |
|---|---|
| No | 21 |
| Yes, but more expensive | 5 |
| Probably (surcharge, quote or own inspection needed) | 3 |
| No response | 1 |
The yes answers generally wanted at least 100-amp service, and the author notes answers change over time. That's another state, years ago, so treat it as a warning sign, not today's Indiana answer.
The step that matters: the day the report arrives, ask the agent quoting your policy, "Will you write this house with active knob-and-tube?" Get it in writing, inside the inspection period. Your lender won't close without proof of insurance.
How much does it cost to replace knob-and-tube wiring?
HomeAdvisor puts a whole-house rewire at $6 to $10 per square foot, or $12,000 to $20,000. If the panel needs replacing too, a 100-amp panel runs $800 to $1,500 and a 200-amp panel $1,300 to $2,000 (HomeAdvisor, updated June 17, 2026). HomeAdvisor's electrician guide gives a wider $1,500 to $10,000 for wiring a house, depending on how accessible the wiring routes are (HomeAdvisor, updated June 19, 2026). All national figures.
InterNACHI's summary of the trade-off is fair: a rewire can take weeks of work and thousands of dollars, weighed against fire and insurance risk (InterNACHI).
What moves the number in an older Indianapolis house: plaster walls (harder to fish wire through and patch than drywall), finished basements and attics that block access, and how many circuits are still live. A partial rewire of a few active circuits is a fraction of the whole-house figure. Get a written quote on the actual house.
Should I ask the seller to replace knob-and-tube wiring?
Ask for the right thing, and get the electrician in first so you're negotiating a real number:
- Active knob-and-tube: a credit or price reduction based on the written quote is usually cleaner than asking a seller to manage a rewire before closing. If your insurer won't write the policy until it's gone, the work has to happen first, and the timeline in the agreement needs to say so.
- Abandoned knob-and-tube: ask only for the electrician's written confirmation that it's disconnected.
- Damaged or buried runs: ask for those specific circuits to be replaced before closing, with a permit.
InterNACHI's advice to buyers is the same: get a replacement estimate and use it to negotiate the price (InterNACHI).
Who does the work: Indiana has no statewide electrician license, so check the city or county. In Indianapolis, the city licenses electrical contractors, and applicants have to pass an exam and get approval from the electrical licensing board first (City of Indianapolis, Contractor Licenses, read October 2026). For a rewire, insist on a permit and the final inspection. Timing: how the inspection period works in Indiana.
Should I buy a house with knob-and-tube wiring?
You can, with your eyes open. Budget the rewire into what you're willing to pay, confirm you can insure the house before the deadline, and plan the electrical work before any insulation or remodeling, not after. Structure Tech's advice is the same three steps: an inspector who knows knob-and-tube, an electrician for whatever they find, and confirmed insurance before you buy (Structure Tech).
Houses with original wiring often have original plumbing, too. If the report also mentions galvanized pipes, get both trades out before the deadline. If you love the character but not the projects, compare honestly with newer options on the new construction vs. resale page.
I'm selling a house with knob-and-tube. What should I do before listing?
Find out what you have before a buyer's inspector does. Have a licensed electrician tell you what's live and give you a written scope and price. If it's all abandoned, get that in writing and hand it to buyers. If it's active, either do the work or know the number so you can price the house or offer a credit with confidence. Buyers who can't get insurance can't close, so the electrician's letter is worth more than you'd think.
Known wiring conditions belong on the Indiana seller's disclosure. More on pre-listing repairs: what to fix before selling.
Why a Realtor Who Built Houses Reads Reports Differently
A home inspection report runs dozens of pages, and almost every item ends with "recommend evaluation by a qualified professional." That wording is there for the inspector's protection. It doesn't tell you which items are a quick fix and which ones change the deal.
I spent about ten years designing houses and running their construction before I sold them. When my clients get their report, we go through it together and sort it into what to ask for, what to take as a credit, what to just fix yourself later, and what needs a specialist before the inspection deadline. If you're buying or selling in central Indiana, I'm happy to do the same for you.
Construction engineer turned Realtor. Straight answers before you sign.
Send Me the Page That Worries You
Tell me the address and the finding. I'll tell you how serious it looks from a builder's point of view and how it usually gets handled in a deal.
Send a MessageWhat's Your Home Worth?
Selling an older home? Start with a realistic price based on recent local sales.
Have a Knob-and-Tube Question?
Send the address and the line from the report. I'll get back to you with how serious it looks and how it usually gets handled.
General guidance from a Realtor with a construction background. Hire the licensed trade for the diagnosis and the fix.
General information from a Realtor with a construction background, not electrical, insurance or legal advice. Cost ranges are national figures from HomeAdvisor (updated June 2026); Indianapolis-area quotes vary. Insurer survey figures are from Structure Tech's 2019 Minnesota survey. Have a licensed electrician evaluate older wiring, and ask your insurer directly about coverage.