Electrical · Built before 1950

Knob-and-Tube Wiring in Homes Built Before 1950

Homes built before 1950 without a documented rewire may still have some of their original knob-and-tube wiring — an ungrounded system that most insurers won't cover.

What it is

Knob-and-tube wiring was the standard residential wiring method into the early-to-mid 20th century: individual insulated wires run through ceramic knobs and tubes, rather than the sheathed cable used today.

Why it matters

It has no ground wire, and its insulation wasn't designed to be packed in with modern attic or wall insulation, which can trap heat around the wire. Most insurers, in Minnesota and nationally, decline to write policies on homes with active knob-and-tube wiring.

What's worth doing next

A full rewire is typically what insurers ask for. Worth confirming with an electrician whether any original wiring remains before budgeting for it — many older homes have already had some or all of it replaced.

Code changes like these are prospective — they apply to new construction going forward, not retroactively to homes already built. A home that predates a given standard isn't out of compliance with anything; it just predates it. Tarn surfaces this as a consideration worth having evaluated, not a verdict on the home.

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Enter the year built alongside an address search, and Tarn checks it against this and every other code-era risk factor automatically.

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Other code-era risk factors