Knob-and-tube (K&T) was the standard way to wire homes from roughly the 1880s to the 1940s. Plenty of it is still in service in older California homes, often mixed with later wiring.
What is knob-and-tube wiring?
Individual wires run through ceramic knobs (that hold wire away from framing) and ceramic tubes (where wire passes through joists and studs), with cloth-and-rubber insulation. It has no ground wire.
Is knob-and-tube wiring dangerous?
Original, undisturbed K&T was not dangerous by design, but after many decades the risks pile up:
- Brittle insulation that cracks when disturbed.
- Buried in insulation: K&T was designed to shed heat into open air. Blown-in attic or wall insulation around it is a concern, and the code restricts it.
- Amateur splices and extensions added over the years.
- No ground, so 2-prong outlets and no protection for modern 3-prong devices.
- Overfusing: oversized fuses or breakers on small old wire.
Will insurance cover a house with knob-and-tube?
Many insurers ask about it, and some decline coverage or require an electrician's evaluation or replacement. Ask your agent before you buy.
How do I know if I have knob-and-tube?
Look (safely, without touching) in an unfinished basement, crawlspace or attic for single wires on white ceramic knobs. Two-prong outlets and a fuse box are hints, not proof. An electrician or home inspector can confirm.
How does replacement work?
K&T is usually replaced circuit by circuit with modern grounded cable, fished through walls to limit patching, with a permit and inspection. Many homeowners start with the highest-risk areas (kitchens, bathrooms, bedrooms, anything buried in insulation). IES can start with a rewire assessment, and we quote replacement from photos or a free estimate.
About these prices: rough starting-at prices from the IES price book. The final price depends on what we find on site, your utility and your city or county. Estimates are free.
Common questions
Is knob and tube wiring safe?
It can be in good original condition, but age, brittle insulation, splices, buried insulation and no ground make it a common concern for inspectors and insurers.
Does knob and tube have to be replaced to sell a house in California?
California does not generally require replacement to sell, but it must be disclosed, and buyers, lenders or insurers may ask for evaluation or replacement.
General information for California homes under the California Electrical Code (based on the NEC). Local rules and inspectors can vary. Not a substitute for an on-site inspection. Never work inside a panel, at the meter or on live circuits.