Homeowner guide
Knob and tube wiring, and what it means for your house
If your St. Charles home predates 1950 — and in Old Town and Frenchtown plenty do — there is a reasonable chance some knob and tube is still in the walls. Here is what that actually means, without the scare tactics.
- How to identify it
- Why insurers ask about it
- Whether it is actually dangerous
- What replacement involves
The short version
Start here
Work down the list. Most situations are answered in the first two rows.
What it looks like
Identification
Porcelain knobs holding individual wires, porcelain tubes where wire passes through framing, and cloth-covered conductors running separately rather than in a jacket.
Where to look
Basement or attic
Look along joists in an unfinished basement or attic. If you see ceramic knobs with wire strung between them, that is it.
Two-prong outlets
Strong hint
Knob and tube has no ground wire. A house full of two-prong outlets is telling you something about what feeds them.
Age of the house
Context
Common in construction through the 1940s, phased out by the 1950s. Homes in Missouri built in the 1950s or before may still have it.
Partly abandoned
Very common
Most of these systems are partly disconnected already. What is still live is a different question than what is still visible.
General guidance for St. Charles area homes. Every house is different — call if you are unsure.
Is it actually dangerous?
Not inherently, when undisturbed
Properly installed knob and tube in good condition, not buried in insulation and not spliced into, can operate safely. The problem is that this describes almost none of it after a century.
Insulation is the real hazard
The system sheds heat into open air. Blown-in or batt insulation added decades later traps that heat against cloth insulation, and that is a genuine fire risk.
Amateur splices
A hundred years of homeowners and handymen tapping into it. Junctions made outside boxes, taped rather than terminated, are where failures start.
Brittleness
Cloth and rubber insulation dries out and cracks with age and heat. Once it flakes off, you have bare conductors in a wall cavity.
No ground
Nothing on the circuit is grounded, so no surge protection works properly and any fault has no safe path. Modern electronics assume a ground that is not there.
Insurance
Some carriers will not write a policy on a home with active knob and tube; others charge more or require replacement within a set period.
The honest answer
What replacement actually involves
It is a rewire, and in a historic home it is a careful one.
Replacing knob and tube means running new grounded circuits to everything the old system fed, and either removing the old wire or abandoning it in place fully disconnected — insurers sometimes have a preference, so it is worth asking yours. The work itself is fishing new cable through existing cavities, which is why access and wall construction drive the cost far more than the wire does. In an Old Town home with plaster walls and original trim, minimizing openings is the whole skill. It can be done all at once or in stages, taking the circuits under insulation and in wet areas first. Either way it is permitted and inspected, and the documentation is what resolves the insurance conversation.
Common questions
What homeowners ask us
How do I know if I have knob and tube wiring?
Look along joists in an unfinished basement or attic for porcelain knobs with individual cloth-covered wires strung between them, and ceramic tubes where wires pass through framing.
Is knob and tube wiring illegal?
No. Existing installations are generally allowed to remain, though extending or modifying them is restricted, and insurers may treat it differently than code does.
Will insurance cover a house with knob and tube?
Some carriers decline it, some charge more, and some require replacement within a set period. Policies vary, so ask your carrier directly.
Is it safe if it has not caused problems yet?
Undisturbed and uninsulated, it can operate safely. The common problems are insulation added over it, decades of amateur splices, and brittle deteriorating conductors.
Do I have to replace all of it at once?
No. Staged replacement taking the highest-risk circuits first is a legitimate approach, particularly in an occupied historic home.
Free estimate
Get a real number for your home
Guides are for planning. For an actual price, tell us what you have and we will give you a firm number.
Related: knob and tube rewiring, whole-home rewiring, rewiring cost, wiring a historic home, signs of electrical problems
Something electrical that is not getting better on its own?
Call for anything urgent, or send the form and we will get back to you within one business day with a real number.