Should You Replace Knob and Tube Wiring?

Knob and tube wiring systems: hazardous and difficult to insure.

Old knob and tube wiring in a house is primed for a short circuit or worse.

 Douglas Sacha / Getty Images

If your home (or a home you’re considering buying) was built between 1880 and 1950, then you might have knob and tube wiring to worry about. An outdated electrical system now considered obsolete, knob and tube wiring can pose a safety hazard, make it hard to insure your home, and cost you thousands to update.

If a home you’re financially invested in has a knob and tube wiring system, it’s important to understand the full scope of what this means and what it may cost you to remedy.

What Is Knob and Tube Wiring?

Knob and tube wiring, sometimes referred to as just K&T, is a type of electrical wiring seen in homes built in the late 1800s and early 1900s. It uses a system of copper conductors, which are run through tubes and held down with porcelain knobs. Unlike modern electrical systems, they have no ground wire.

Why Is Knob and Tube Wiring Dangerous?

There are a few risks associated with knob and tube wiring systems. For one, the lack of ground wiring means these systems pose a higher risk of electrical fire. Ground wires protect you and your home in the event of a short circuit or other fault by redirecting electricity to ground via the wire, rather than through you. Without these in place, the risk of fire and electrocution increases.

Having insulation near any knob and tube wiring can also increase fire risk, as it traps heat and allows it to build over time. As of 2008, the National Electrical Code specifically requires that knob and tube wiring not be covered by insulation, particularly within walls, ceilings, and attics.

The Trouble With Knob and Tube

Problems with knob and tube wiring include:

  • Increased fire risk.
  • Lack of ground wiring.
  • Inability to service three-pronged appliances.
  • Deterioration over time.
  • Improper modification by previous homeowners.

Insurance companies often refuse to offer homeowners insurance for homes with knob and tube wiring, due to the increased fire risk they present.

How to Tell If You Have Knob and Tube Wiring

Knob and tube wiring is often hidden behind walls and in difficult to see places. Your home inspector might note it when evaluating your property, but if they don’t, that doesn’t mean you don’t have any. If your home was built in between 1880 and 1950, then consider having an electrician out to check for knob and tube wiring. It may be hidden behind walls or within insulation in the attic.

Do not go looking for knob and tube wiring yourself. Hidden, exposed wiring can present an electrocution hazard.

What to Do If You Have Knob and Tube Wiring in Your Home

There are no building codes that say knob and tube wiring must be completely removed, according to the International Association of Certified Home Inspectors. Still, they can present a fire risk and safety hazard to both your home and its inhabitants. It also may make your home hard to insure.

If you do find knob and tube wiring your home, have a trained electrician evaluate the system and ensure it is installed properly and that no unsafe modifications have been made. If the system is installed safely (or can be repaired), then you can leave the system in place if desired. There are limitations to using knob and tube wiring, though. Knob and tube wiring cannot be used to power kitchens, bathrooms, laundry rooms, or outdoor areas due to its lack of grounding. It is also not for use in rooms with multiple large appliances.

How to Replace It and What It Will Cost

In many cases, replacing the knob and tube system is your best bet. The cost of removing outdated wiring and replacing it will vary depending on several factors, including the square footage of your home, the difficulty of the job, and the area where you live; it can amount to thousands of dollars. Make sure to get quotes from a number of qualified electricians before moving forward. Keep in mind that rewiring a home can be a time-consuming process, so you may need to arrange temporary housing should you opt to replace the system.

If you’re purchasing a home with knob and tube wiring, you might consider negotiating the system’s replacement costs as part of your deal. You could also ask the seller to replace the system before move-in. Ask your real estate agent for advice on the best strategy in your specific case.

Article Sources

  1. International Association of Certified Home Inspectors. "Knob-and-Tube Wiring," Accessed Oct. 1, 2019.

  2. Federal Alliance for Safe Homes. "Availability of Insurance," Accessed Oct. 1, 2019.

  3. Center for Energy and Environment's Home Energy Hub. "What to Do If You Have Knob-and-Tube Wiring," Accessed Oct. 1, 2019.

  4. Weatherization Training Center at Pennsylvania College of Technology. "Retrofitting Knob and Tube Wiring An Investigation into Codes, Assessment, Wiring Practices and Cost," Accessed Oct. 1, 2019.