What is Knob and Tube Wiring?

Knob and tube wiring was an early standardized method of electrical wiring used in buildings in the United States from about 1880 to the 1940s. It consists of single insulated copper conductors passing through holes in joists and studs and supported by ceramic knobs attached to the structural members. The knob served to keep the wire away from the lumber and to provide air space for cooling. Where wires entered a wiring device, such as a lamp or switch, or were pulled into a wall, they were protected by flexible cloth or rubber insulation called loom.

The two or more conductors were separated from physical contact with each other by approximately one inch of air space. This air gap helped to dissipate heat generated by the conductors, reducing the risk of fire. Since air was free to circulate over the wires, smaller conductors could be used than required in cables. By inserting porcelain tubes or "bushings" through joists, wires could pass without coming into contact with the lumber. Loops allowed for expansion and contraction of conductors due to temperature changes.

Key characteristics:

Is Knob and Tube Wiring Dangerous?

Knob and tube wiring that is in good condition and has not been altered or modified can be safe to use. However, there are some potential concerns, including:

So while K&T can still function safely in some cases, deterioration or improper alterations over the decades can make it potentially hazardous. Any homes with knob and tube wiring should have it thoroughly inspected by an electrician before renovation.

Why Rewire Homes With Knob and Tube Wiring?

There are several compelling reasons you may want to rewire a home rather than leaving old knob and tube wiring in place:

In summary, rewiring eliminates the fire, shock, and power reliability risks of old knob and tube wiring. The peace of mind and improved home function are worth the investment.

How to Rewire a House With Knob and Tube

Rewiring a house replaces old dangerous wiring with safe, reliable, modern wire meeting electrical code. The basic process includes:


Wiring Installation

Finishing Touches

Safety should be the top priority during a knob and tube rewiring project. Always turn off power at the main breaker panel before working. Follow all electrical codes and permit requirements. Consider having an electrician do the more complex aspects of the rewiring.

Typical Cost to Rewire an Old House

The cost to fully rewire an older home with knob and tube wiring averages $8,000 to $15,000. However, costs can vary widely based on factors like:

Rewiring a 1000 sq ft house yourself might cost $2,000-$4,000 for materials like breakers, receptacles, and NM cables. Hiring an electrician could run $6,000-$10,000 including labor for a full rewire.

Critical needs rewiring of the most essential electrical circuits could potentially cost $2,000-$6,000, but leaves hazards. A whole home rewire is recommended for safety, function, and value.

Get quotes from at least 3 local electricians to find the best deal. Many provide free estimates to evaluate your specific needs.

Tips for Rewiring an Old House With Knob and Tube

Work safely and get all required permits and inspections. The effort to rewire an old knob and tube house is worth it for safety and peace of mind.