Knob-and-Tube Wiring in Janesville, WI

What it is

Knob-and-tube runs single insulated wires along the framing on white porcelain knobs and through the joists in porcelain tubes, with the hot and neutral apart rather than together in one cable. InterNACHI dates its common use to about 1880 through the 1940s, and notes it is not inherently dangerous (InterNACHI). EC&M describes it as a Class C wiring method allowed only in dry locations, unchanged in the code from 1915 to 1993 apart from better insulation, and placed in Article 394 of the National Electrical Code in 2002 (EC&M, 2022).

Where it turns up here

4,173 of Janesville's 29,330 homes (14.2%) were built in 1939 or earlier. Beloit's share is 26.9% (3,915 homes), and its median home was built in 1957 (Census ACS 2020-2024). The Census records when a house was built, not what is in its walls: many of these houses were rewired long ago, some only partly. The town by town numbers are in how old is the wiring in Rock County.

The insulation problem

Knob-and-tube was designed to shed heat into open air. EC&M's code column warns that concealed knob-and-tube embedded in thermal insulation can become a real fire hazard, which is why NEC 394.12 bars it from hollow spaces that insulation fills (EC&M). That makes the order of work important: get the wiring checked, and if needed replaced, before blowing insulation into an attic or walls in an old house.

Replacing it

A rewire is new wiring, so it is permitted, and in Janesville any wiring that will be covered has to be inspected before it is covered (City of Janesville). PermitDeck's Milwaukee table puts a whole house of about 1,800 square feet at $8,580 to $14,520 (PermitDeck). Plaster walls, attic and basement access, and how much old wiring is still live are what move the price. Many owners do it in stages: the circuits still on knob-and-tube first, kitchens and baths next. An electrical inspection to map what is there runs about $150 to $350 (cost page), and the work often pairs with a panel upgrade.