Knob and Tube Wiring - Replacing for Insulation

Knob and Tube Wiring (sometimes called K & T)
You can read all about Knob and Tube wiring on wiki, and other places on the web, but I'll boil down what I've learned so far. I'm not an electrician.

Knob and Tube wiring in our attic. You could call this photo "old meets new". (Note: click on photos to enlarge them)

• Knob and Tube was installed in homes from about 1880-1930s.
• Knob and Tube wiring is not grounded.
• Wall switchers were often placed on the neutral wire, which turns the circuit off, but current is still fed to the light/outlet.
• Over time the original wire insulation (fabric or rubber) becomes brittle.
• Originally safe Knob and Tube installations are often compromised with unsafe alterations.
• Knob and Tube needs to be suspended in open air to allow heat to dissipate.
• Most insurance companies will not insure houses with Knob and Tube, unless it is deemed safe by an electrician or home inspector.
• Hire a qualified electrician, to inspect your Knob and Tube wiring.
• Hire a qualified electrician, to replace your wiring if that is the plan.
• Home inspectors will note it as a negative to buyers when selling your home.
• Removing it now will save you headaches down the road.
• Keep the ceramic parts and sell them on ebay. People with restoration projects may buy them.

Knob and Tube Wiring and Insulation
The important point for me is the one about Knob and Tube wiring and insulation. I recently had a home energy audit preformed by Energy Audits Unlimited (highly recommended), and they found places in my house that needed insulation, but before I could insulate, I needed to remove the Knob and Tube.

As stated above, Knob and Tube and insulation (loose fill or fiberglass batts) don't mix, because it is essential that the wires are free to dissipate heat. If you insulate around them, it is a fire hazard. In fact, the United States National Electric Code (NEC) section 324-4, forbids the use of loose, blown-in, or expanding foam insulation over Knob and Tube wiring.

Replacing Knob and Tube
Sure I could work around the old wiring and only insulate where there wasn't any, but I've been meaning to replace the Knob and Tube for a while now. So I decided to look into it. The rest of this article addresses what to expect when replacing Knob and Tube wiring.

This is a view from our basement. With the knob and tube installed. Unfortunately, I don't have more photos from down here. I had places where the rubber insulation had fallen off, exposing a few inches of bare wire in many places. I also had wire that had fallen off of it's ceramic knobs and was resting on steam pipes, other wires, and so on. Most of our house's wiring had been updated already, but like most old houses, it was like a museum of home wiring history. You can see the blue and black wires above from different upgrades.

About 10 years ago the previous home owner upgraded all but 2 lines of Knob and Tube, which still fed a little less than half the house. So my upgrade was not a whole house upgrade.

I called 4 electricians for quotes. One never called back, so I had 3 actually come to the house to make bids. The bids were quite varied, but to be fair, that is because each was offering differing solutions, and options in the upgrade. In the end I went with the guy I felt most comfortable with. I liked him because he insisted that all of the work he does meets code, where others might take shortcuts, and in order to do so he checked with the local inspector for a few code questions that he and I had, prior to me paying him a dime. I went with J & M Electrical, who I highly recommend, as they did excellent work, and were very professional in all ways. Thanks guys for a job well done.

The work took 2 days. On my drive home from work, after day one, I didn't know what I'd see. I was expecting anything from minimal damage, to major drywall and plaster damage in all rooms. What you see above is what I saw, only one hole cut. They need to cut these in order to fish new wire around hard to access areas. Shown below you'll also see damage around a light switch and an outlet.

After all was said and done, there were only 2 holes cut, like this one, and they kept the cut outs and reinstalled them. I'll be doing minimal drywall repair here and it'll be history.

Here's a light switch with damage to the plaster wall. This was the only switch with damage, which is quite impressive considering they had to fish wires through a 100 year old home with god knows what in the walls. Perhaps the damage was from putting in a new electrical box. I'm not sure really.

There were about 3 outlets that had minimal damage like this. I was expecting there could be walls and ceilings with holes cut all over the house, so I'm very please.

And here is the finished project. Yes that's the right photo! When you get your house rewired, don't expect them to run wires where they were before. They feed new lines to all the switches and outlets but they may take different paths, than where your knob and tube was. They asked whether I wanted to keep the ceramic fixtures and I said yes, as they have some value (not sure what yet), to people (who? I'm not sure but people that are restoring things? God knows what, perhaps museums?) In the basement they did cut the wires down between the knobs. Here they left it all intact (besides being cut at the floor), which is a good thing for you because I didn't have a before photo!

Here's an after shot in the basement with a new junction box.

Another after shot with a new junction box and old wire cut off of knobs.

New wires shown in this after shot. If your are rewiring, you might as well run cable, internet, and any other lines you might want (an excellent suggestion made by the electrician). The blue and black lines are new, which run up to our unfinished attic, which might be finished in the future. When they are pulling lines, pulling more lines isn't much more time/work.

In some ways I miss the old Knob and Tube and the nostalgic craftsmanship of years gone by. We bought an old house for "character" you know. But it's much better to know that my house won't burn down, the kids will be safer with grounded outlets, and that I can now insulate to my heart's content, and save money on heat... and save the planet at the same time... being "green".

Wikipedia: Knob and Tube Wiring
Old House Web: An article about Knob and Tube by William Kibbel III—The Home Inspector
Old House Web: Evaluating your Homes Wiring System
Old House Web: Electrical Issues in Old Houses
This Old House: Tracking Down Knob-and-Tube Wiring
Retrofitting Knob and Tube Wiring–An Investigation into Codes, Assessment, and Wiring Practices and Cost: Pennsylvania Department of Community and Economic Development (PDF)
Helter Shelter, "Knob and Tube" By Walter Jowers

Service Resources
J & M Electrical - Highly recommended
Energy Audits Unlimited - Highly recommended

Disclaimer: This is what I did. This does not mean this is the best way, the right way, to building code, or even safe for your needs. So you are on your own with your project. I make no promises about the information presented here. I'm just a do-it-yourselfer, not a professional at all, sharing my story. So if something goes wrong with your project, you are on your own. Good luck, and have fun!

All content and photos, copyright 2008, Dover Projects.

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  1. Very interesting article -- exactly the same problem I have in my home/office: knob and tube, in my case a lot of the insulation has frayed, and I have plaster walls, in an 1890's house.

    Here's my question: can you give me a rough idea of the cost? I'm trying to budget for this. Thanks,

  2. I think our project cost was $2,400, if I remember correctly. But that won't tell you much, as your project will be unique to your situation. Also we had a few extras, like TV cable and internet cable run to the attic while they were here. Electricians give free estimates, so that might be the best route to go for an idea of cost.

  3. thank you learned what i needed to know

  4. Great! Glad the article was useful--Peter

  5. After reading several items on this subject, your perspective did give me some fresh outlook.
    Thank you for the useful article.

  6. Thanks for your feedback! Good luck with your project.--Peter

  7. I love this article because I am about to purchase an old 1930's house.I am in the process of researching everything I can or need to do to make it a safe home. This was very helpful.

  8. anonymous: glad it could help you!--Peter

  9. NEW!!! DOVER PROJECTS ON FACEBOOK! Join in with your DIY spirit! Click on the BIG blue box for "Facebook, Dover Projects" in the right column above! See you there!--Peter

  10. Hi Peter,

    I work for Old House Journal magazine and we're running an article on how to properly rewire an old house in our next issue. We would love to use a few of your images here on knob and tube wiring to go along with the article. Please let me know if you're interested and I can give you more details. Thank you and great shots!


  11. Hi Jenny,

    Would love help you out. Very exciting. I of course have many more outtakes that I didn’t post in this article and they are hi-res. Well... Higher res...


  12. Hi Peter,

    I am a collector of knob and tube wiring objects and I was wondering if maybe you still had anything from the knob and tub wiring. If you do would you be interested in selling any of it.

    Thank you for your time,

  13. Kolton, we do have parts. What's the going rate on these types of things? Certainly an interesting thing to collect. How did you get started? How long have you been collecting?—Peter

  14. Hi Peter. Thanks for your article. I enjoyed reading it and it was very informative. We are buying a home built in 1940 in San Diego area and just discovered it's knob and tube. Initial estimates from two electricians are $10,000 and $20,000 to rewire this small house - not even 1000 sq.ft. The higher estimate contractor talked about pulling permits for the job...did you have to do that? The house is lathe and plaster so access through the walls may be difficult. Is yours drywall? We'd love to be able to get away with a $2,400 repair. Did the Old House Journal write the article they commented about. Thanks for posting. Nancy

  15. Do you still have knob and tube parts for sale thanks Ben please reply to


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