Knob & Tube Wiring: Identification, Insurance, & Replacement

Knob and Tube Wiring

What is Knob and Tube Wiring?

Knob and tube wiring is cloth wiring that is ran through a “knobs”, which are the white ceramic cylindrical holders, and “tubes” that protect wiring through wood. This type of wiring was commonly installed from the 1880’s to the 1940’s.

Knob and tube wiring is inherently dangerous, however, it is considered outdated and a possible fire hazard.

Where Can You Find it and what does it look like?

This type of wiring can typically be found in attics. On the other hand, it can also be found in crawlspaces or in the walls.

The wiring is typically black cloth while the knobs and tubes are white. Most updated wiring is yellow in color and made out of romex.

Knob & Tube Wiring

What is Wrong with Knob & Tube?


  • Due to its age, the system is not grounded. Since circuit grounding was not installed until the 1960’s.
  • Modifications. In most cases, the wiring has been unprofessionally modified. For example, not using electrical tape of junction boxes, exposed wiring, or improper wiring.
  • Poor wiring insulation that can be a fire hazard due to deterioration.
  • Wiring stretches/sags overtime.
  • The system cannot typically handle the energy demand of the today’s average home.

One of the bigger issues with with knob & tube is how it is designed. The outer covering is made to dissipate heat caused by electric flow. In normal conditions, this a good idea to prevent fire hazards. But, with today’s insulation practices in attics, walls, and crawlspaces, the packed insulation against the wiring prohibits the heat dissipation.

Obtaining Insurance

Getting insurance with this type of wiring can be very difficult. Typically, homeowners will have to pay much higher premiums or replace the knob & tube wiring altogether. Moreover, in some cases, insurance companies will want all knob & tube wiring removed even it is not active.

Replacement Cost

In order to remove and install new wiring throughout a home can depend on the location and size of the home. However, on average the cost for K&T replacement is about $3,500-$8,000.

Final Notes

Although it is not required to replace knob and tube wiring and new construction homes are no longer using it, homeowners should consider replacing it.

Due to the fire hazards, difficulty with Insurance, and outdated wiring systems, it is generally recommended to replace it.

More Resources on K&T


Mr. Electric

Aaron Shishilla

Author Aaron Shishilla

Aaron Shishilla is the youngest registered professional inspector in Florida. Coming from a family-owned home inspection company and now the marketing manager at Waypoint.

More posts by Aaron Shishilla

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