Knob and tube wiring replacement cost

Replacing knob and tube wiring costs $8,000 to $30,000 for a typical house, typically around $15,000, or roughly $4 to $12 a square foot. Partial replacement of the worst circuits is $2,000 to $8,000.

Knob and tube was standard from the 1880s to the 1940s. Where it survives it is at least eighty years old, it has no ground, and it is the single most common reason an insurer declines to cover a house.

What it costs

The drywall and painting rows are the ones people forget. A rewire in a finished house means holes in walls and ceilings, and putting those back is a separate trade.

What is actually wrong with it

Knob and tube itself was well engineered for its era. Individual conductors run through ceramic tubes where they pass through joists and are supported on ceramic knobs, with air space around them for cooling. Installed correctly and left alone, it is not inherently dangerous.

The problems are what happened since:

No ground. Every outlet is a two-prong, and every modern appliance expecting a ground does not have one.

Insulation age. The rubber and cloth insulation becomes brittle after eighty years and cracks off where the wire has been flexed or heated, particularly at fixtures.

Buried in insulation. The system relies on air circulation for cooling. When attics were insulated in the 1970s and 80s, the wiring was buried, and it now runs hotter than it was designed to. Most current code prohibits covering it for this reason.

Amateur extensions. Eighty years of people splicing modern cable onto knob and tube in an attic, often without a box.

Not enough circuits. A 1920s house was wired for lighting and a radio. It has two or three circuits where a modern house has twenty.

Insurance is usually the forcing function

Many insurers will not write a policy on a house with active knob and tube. Others require an inspection, a specific electrician's letter, or remediation within a set period. This is frequently how buyers discover it exists, during the mortgage process.

If you are buying a house with knob and tube, get insurance quotes before the inspection period closes. It is the item most likely to make a purchase impossible on schedule.

Partial or full

Full rewire is the complete answer: new panel, new circuits, grounded outlets throughout, and the house is done for fifty years.

Partial rewire replaces the knob and tube that is active and leaves abandoned runs in place. Insurers vary on whether they accept it, and the answer depends on whether they want no knob and tube in the house, or none energized.

Ask the insurer what they need before deciding, because the difference is $8,000.

Doing it in phases is legitimate and cheaper per phase when walls are already open for other reasons. A kitchen remodel is the moment to rewire that part of the house.

What a rewire actually involves

Cable is fished through existing walls where possible, and where it is not, small access holes are cut and patched. In a house with plaster and lath, expect more holes and more repair than in drywall.

Realistic expectations for a 1,500 square foot house: two to four weeks, holes in most rooms, and the electricity off in sections rather than all at once. Living in it is possible and unpleasant. It is a much easier job in an empty house, and if a rewire is in the plan for a house you are buying, doing it before moving in saves both money and temper.

Frequently asked questions

Is knob and tube illegal?

Not to have. Most codes prohibit installing new knob and tube and prohibit extending existing runs or covering them with insulation. Existing installations are generally grandfathered.

Can I just add a GFCI to protect it?

GFCI protection is permitted on ungrounded circuits and it protects people from shock. It does not address brittle insulation, undersized circuits, or overheating under insulation, and insurers rarely accept it as remediation for knob and tube.

How do I know if I have it?

Look in the basement or attic for individual black cloth-covered conductors running through white ceramic knobs and tubes, spaced apart from each other rather than in a sheathed cable. If the wires run separately with air between them, that is it.

Is it dangerous right now?

Undisturbed, in good condition, not overloaded and not buried in insulation, it has lasted a century. The risk comes from age-hardened insulation, amateur splices and modern loads on circuits designed for a lamp. Those are common enough that the caution is warranted.

Can I insure a house with it?

Some insurers will, often at a higher premium, sometimes with a remediation deadline. Shop specifically for this before committing to the house, and get it in writing.