Knob and tube wiring: risks, insurance, $12,000 to $35,000

National figures. Plaster walls, finished ceilings and a fuse box that has to go with it push a job toward the top.

Do this now: if you have knob and tube wiring

Knob and tube is not an emergency by itself; what matters is the condition and what has been done to it. Start with these checks, none of which involves touching a wire or opening the panel.

1. Do not open the panel cover or touch exposed wiring. A visual look in the attic or basement from a distance is enough.
2. Note the warning signs the CPSC lists: fuses that blow or breakers that trip often, dim or flickering lights, sparks, sizzling or buzzing, warm switch plates or outlet covers, a burned odor, damaged insulation, or shocks. Any of these: call now, and see emergency electrician for a burning smell.
3. Check whether insulation is piled on it. Attic insulation blown over live knob and tube is the single condition every source flags: GuideOne says covering the wires removes their cooling and raises the fire risk, and the 2008 NEC bars it in insulated spaces (InterNACHI).
4. Unplug heavy loads from old circuits. InterNACHI says not to run excessive appliances on K&T and never to use it in kitchens, bathrooms, laundry rooms or outdoors, because it has no ground.
5. Get it inspected. HomeGuide prices an inspection at $100 to $200. The CPSC says homes 40 to 100 years old it investigated had never been inspected since they were built.
6. Call the electrician line with the house's age and square footage, whether the panel is fuses or breakers, and whether the attic is insulated.

Is it urgent? When knob and tube becomes dangerous

Knob and tube is dangerous when it is buried in insulation, brittle, overfused or spliced into, and Washington State's electrical rule sets the test in writing: insulation may stay over it only after a licensed contractor certifies no insulation failure, no improper overcurrent protection and no improper splices.

• Call today: any CPSC warning sign above, scorching at a fixture, or a fuse larger than the circuit rating. InterNACHI says homeowners often installed fuses rated too high for the wiring, which heats it.
• Call this month: insulation in contact with live K&T; cloth insulation that is cracked or crumbling (GuideOne says it dries out and exposes bare wire); extension cords used as permanent wiring (CPSC).
• Plan it: intact, uninsulated, uncovered K&T on lightly loaded lighting circuits, which the Washington rule and InterNACHI both treat as allowed to remain when certified. A rewire is then a planned project, priced on rewire house cost.
• Weatherization crews treat it as a hazard: the DOE and NREL work specification requires 3 inches of clearance around live knob and tube and caution tape visible from 5 feet before insulating.

What knob and tube wiring is and how to recognize it

Knob and tube wiring was installed from about 1880 to the 1940s in InterNACHI's account and "up until the year 1950" in GuideOne's insurer bulletin, so a house built before 1950 that has never been fully rewired may still carry some of it.

• What you see: single wires, not a cable, running separately a few inches apart; white porcelain knobs nailed to joists holding the wire; porcelain tubes where a wire passes through a joist (InterNACHI).
• Two wires, no ground: GuideOne says only a hot and a neutral run to each fixture; InterNACHI says it cannot serve three-pronged appliances. Two-slot outlets on an old circuit are a clue.
• Cloth and rubber insulation that dries, cracks and peels (GuideOne; InterNACHI).
• In-wall splices with no box: GuideOne lists unboxed splices among the hazards; InterNACHI says unsafe modifications are far more common on K&T than on modern cable.
• Often with a fuse box and a service under 100 amps (GuideOne), both undersized for a modern house.

Why insurers balk at knob and tube wiring

"Some providers will offer coverage for knob and tube wiring while others will deny you outright," American Family Insurance says, and a home that is insured may face higher premiums; InterNACHI says many insurers refuse K&T homes outright because of fire risk.

• What an insurer may require: American Family says wiring may need upgrading before new coverage goes live, and recommends a qualified electrician's inspection and bids. InterNACHI says exceptions are sometimes made when an electrical contractor certifies the system as safe.
• Why: GuideOne, writing for insured organizations, says any knob and tube in a building presents a potential fire hazard and that "This wiring should be replaced by a licensed electrical contractor." Triple-I's home buyer's guide puts it plainly: if the inspector raises questions, your insurance company will as well.
• Scale of the risk: NFPA counts an average of 31,647 home fires a year from electrical distribution or lighting equipment (2011 to 2023), as cited by ESFI.
• Buying a house with K&T: InterNACHI tells buyers to get a replacement estimate and negotiate the price. Get the insurance quote before the inspection contingency expires. More on what policies cover: does homeowners insurance cover home repairs.

Knob and tube wiring replacement cost

Replacing knob and tube wiring costs $12,000 to $35,000 on average in HomeGuide's February 2026 guide, or $8 to $17 per square foot, and $12,000 to $36,600 in Angi's August 2026 data, or $10 to $20 per square foot.

For a 2,000 square foot house that is $16,000 to $34,000 (HomeGuide) or $20,000 to $40,000 (Angi). HomeGuide's rewire guide puts any old-house rewire at $10,000 to $30,000, so K&T sits at the top of the range because the old wire has to be found, cut dead and often left in place while new cable is fished through plaster. A new panel, if the fuse box goes with it, is $518 to $2,193 for most jobs in HomeAdvisor's figures; see electrical panel upgrade. Per-room and partial rewire prices are on rewire house cost.

Can knob and tube be left in place? What the rules say

Yes, in most places, if it is in good condition and not buried: Washington's rule lets thermal insulation go over existing K&T only after a licensed contractor's written certification, with Type S fuses or circuit breakers on every circuit, and "Foam insulation may not be used with knob-and-tube wiring."

• The NEC rule: InterNACHI says the 2008 code requires that K&T not be covered by loose, rolled or foamed-in insulation in walls, ceilings and attics, and that local jurisdictions may or may not adopt it; California allows contact under conditions including a licensed contractor's certification.
• No extensions without inspection: Washington requires the electrical inspector to inspect all repairs, alterations or extensions to the system.
• No new construction: InterNACHI says K&T is not permitted in any new work.
• Clearance: the DOE and NREL specification for weatherization crews is 3 inches around live K&T.

Knob and tube vs aluminum wiring

Both are older wiring types that insurers may decline, American Family says, but aluminum branch wiring dates from the 1960s and 1970s and is a different fix; HomeGuide prices any old-house rewire at $10,000 to $30,000 and the rewire page covers aluminum separately.

Hiring an electrician for knob and tube

• Ask for an inspection first ($100 to $200, HomeGuide) with a written list of what is live, what is dead and what is buried in insulation.
• Ask for a per-square-foot price and whether the panel is included.
• Ask who pulls the permit and schedules the inspection; Washington's rule has the inspector check every alteration.
• Ask for the certification letter your insurer wants, in writing, when the job is done.
• License. Ask for the electrician's license number and check it with the state board; the electrician license table shows who licenses electricians in each state.

Hub: electrical repair. Rates: electrician cost. Symptoms: lights flickering and breaker keeps tripping. Calls go to an independent electrical company that serves your area; how calls work.