Is Knob and Tube Wiring a Reason Not to Buy a Home?


If you're looking at antique homes, you may come across Knob & Tube wiring, which is something not many of us are familiar with. An excellent Wiki is here. But as far as purchasing a home in MA, I've embedded some practical advice here. Let's look at some Myths and Facts about Knob and Tube.

Statement: Knob & Tube Wiring is dangerous.

Upgrading Knob and Tube Wiring

is a Big Job - But can be Done.

This is mostly a myth, but has some practical truth to it. Knob and Tube has many problems, two of which are that it is easy to interfere with the installation, and the components of common Knob and Tube degrade over time. Both of these issues can decrease the safety of the installation, making Knob and Tube unsafe.  An example is the cloth insulation over the wires wasn't meant to be 90 years old, and it often is at this point. Also, it's designed not to be covered in insulation or any thing else, as the wires need to be exposed to air to dissipate heat, however many home owners add insulation to their home, and when done improperly, insulation could degrade the safety of the Knob and Tube. It is true that Knob and Tube does not have a ground wire, and ground wires today are largely for safety. Lastly, most Knob and Tube installations are not designed to handle the load of todays household electrical equipment, and too much load on a wire is unsafe. Most of the reasons make Knob and Tube a poor choice for most homeowners.


Statement: Knob and Tube must be replaced in all homes today.Another myth! But it could be difficult to get affordable insurance if you wish to keep the Knob and Tube . As it is difficult to keep Knob and Tube "Safe" most insurance companies are adding to the premiums of homes that are known to have substantial Knob and Tube.

Statement: Upgrading Knob and Tube Wiring is expensive.

This one is usually true. Since you basically have to "rewire" the sections of Knob and Tube that you are replacing, this is a manually intensive job, and labor rates for electricians are not cheap. So the more you have, the more expensive the replacement will be. It will be hard to get estimates too, as the cost can be highly variable, depending on how difficult it is to get to the various outlets and circuits.

Statement: You shouldn't ever buy a home with Knob and Tube

Definitely a myth. You should be aware of the safety risks, maintenance issues and potential costs, and factor that into your decision about what you will pay. But its certainly a solvable issue, and not one that should override your decision if you've found that perfect antique. It should be on your list of things to upgrade in most cases.