Knob and Tube Wiring
Knob and tube wiring was used in US homes from about the 1880s to the 1940s. It has no ground wire, its insulation becomes brittle, and it is often modified unsafely. Many insurers will not cover homes that still have it. Replacing it usually means rewiring, commonly $8,000 to $30,000 depending on house size and access.
Typical pro cost
$8,000 to $30,000
- Urgency
- Plan soon
- DIY difficulty
- Hard
- Time to fix
- Several days to weeks (pro)
- Prices
- US typical range
Last reviewed September 2026
Signs it's this problem
- Porcelain knobs and tubes in the attic or basement
- Single cloth-covered wires running separately
- Two-prong outlets throughout the house
- Home built before about 1950
- Insurer or inspector flagged it
Common causes
Age
The rubber and cloth insulation dries out and cracks after decades.
No ground
Without a ground wire, it cannot safely serve three-prong outlets or protect modern electronics.
Buried in insulation
It was designed to shed heat into open air; blown-in insulation can make it overheat.
Unsafe modifications
Decades of amateur splices and extensions create fire risks.
How to fix it, step by step
- 1
Look in the attic, basement and crawl space for ceramic knobs, tubes and separate single wires.
- 2
Do not disturb, pull on or cover the wiring with insulation.
- 3
Have a licensed electrician inspect and test it, and ask whether any of it is still live.
- 4
Ask your insurer what they require; some want full replacement, others an electrician letter.
- 5
Get quotes for rewiring; phased replacement of the most-used circuits is sometimes possible.
- 6
Budget for drywall and plaster patching after the work.
Tools and materials
- None: this needs a licensed electrician
Approximate DIY cost: Not a DIY job
Call a pro when
- Any work on knob and tube circuits
- Insurance or home sale requirements
- Signs of heat, burning smell or flickering lights
Knob and Tube Wiring cost
| Job | Typical cost |
|---|---|
| Electrician inspection | $150–$500 |
| Rewire a small house (under 1,500 sq ft) | $8,000–$15,000 |
| Rewire a larger house | $15,000–$30,000 |
| Wall and ceiling patching after rewiring | $1,000–$5,000 |
Ranges are typical US prices compiled by FixHomeCost. Prices vary by region, home and contractor, so compare 2–3 local quotes.
Common questions
Is knob and tube wiring illegal?
It is generally not illegal to have existing knob and tube wiring, but new installations are not allowed, and many codes restrict extending or modifying it.
Can I get homeowners insurance with knob and tube wiring?
Some insurers refuse coverage, charge more or require an electrician inspection or replacement. Shop around and ask about requirements.
Can knob and tube wiring be partially replaced?
Yes, electricians often replace it in phases, starting with kitchens, bathrooms and heavily used circuits.
How do I know if knob and tube wiring is still active?
An electrician can test it safely. Many homes have abandoned sections left in place alongside newer wiring.
Related guides
This is general information, not a professional inspection. See how we research costs.