Knob-and-Tube Wiring in Older Boston Homes: What Insurers Require and What Replacement Actually Involves

A lot of houses in Dorchester, Quincy, and Cambridge built before 1950 still have knob-and-tube wiring somewhere in the walls. It is not illegal, but it is getting harder to insure. Here is what carriers are asking for, how to tell if you have it, and what a licensed electrician does to replace it.

How to tell if you have it

Look in the basement or attic for single black or white cloth-covered wires running separately, held off the framing on white ceramic knobs and passing through joists in ceramic tubes. Modern wiring runs as a single flat cable with two or three conductors inside. If the panel has a mix of old screw-in fuses and newer breakers, there is a good chance some circuits upstream are still knob-and-tube.

Why insurers care

Knob-and-tube was designed to run in open air. When it is buried in blown-in insulation, the heat it gives off cannot escape, and the rubber insulation on the wire, now 80 to 100 years old, cracks. Most Massachusetts carriers will not write a new homeowner policy on a house with active knob-and-tube, and several are requiring replacement at renewal or when a house changes hands. That is the moment we usually get the call: a buyer's insurance quote comes back with a condition attached.

What replacement involves

A licensed electrician traces each knob-and-tube circuit from the panel, runs new cable to every outlet, switch, and fixture on it, and disconnects the old wire. In an occupied house with plaster walls that means fishing wire through finished spaces and opening small access holes, which we patch and paint after. On a typical two-family in Dorchester it takes three to six days of electrical work plus a day or two of patching. The permit and inspection are part of it; the inspector signs off before the walls close.

While the walls are open

If a rewire is happening anyway, it is the right time to upgrade the panel to 200 amps, add circuits for a kitchen or bath remodel, or run the dedicated line for an EV charger. Doing it in one permit and one round of patching is cheaper than coming back for each.

Cost

Depends on how many circuits are still old and how hard the walls are to get into. A partial replacement of a few circuits can be a few thousand dollars; a full rewire of a 1920s two-family is a larger project. We give a fixed price after walking the house with the panel open, and we put the insurance letter together when it is done.