Knob and tube wiring and home insurance in New York

Look in the attic and the basement, where framing is exposed. Knob and tube runs as two separate wires, spaced apart, clipped to white porcelain knobs along joists and passing through porcelain tubes where it crosses framing. Splices are often wrapped in cloth tape and hang in open air.

Inside the living space, the clues are indirect: two-prong outlets everywhere, a fuse box or very small service, and ceiling fixtures on round metal boxes. None of those proves it on its own, but together they are worth a closer look.

The system was designed to shed heat into open air. A century later, many runs are buried under attic insulation that traps that heat, and the rubber and cloth insulation on the conductors has dried and cracked. There is no equipment ground, and decades of additions have spliced newer wiring into old runs.

Insurers do not inspect your attic; they price risk from questionnaires. Knob and tube is one of the items that gets a policy declined, surcharged or given a deadline to replace it, alongside fuse boxes and some older panel brands.

Just over 64 percent of the city's housing was built before 1960, and the houses from the earliest decades are where knob and tube survives. Queens is a good example: about 63 percent of its housing was one- and two-family houses by 1960, and much of that stock, in places like Woodhaven and Richmond Hill, was built before modern wiring.

Apartment buildings are less likely to have it in the units, since many were rewired over time, but it can still turn up in older brownstones and row houses in Brooklyn and in single-family houses on Staten Island.

Replacement means identifying every run that is still live and replacing those circuits with grounded cable. Old conductors hidden in walls are disconnected at both ends, tagged and left in place rather than pulled out, which avoids tearing up plaster. Attic and basement runs are replaced first because they are exposed and easiest to reach.

The job usually pairs with a panel or service change, since knob and tube houses rarely have an adequate service. Published figures put knob and tube rewiring at $10,000 to $30,000 when combined with a service upgrade from 60 amps, while a whole-house rewire in the New York area runs roughly $2,500 to $5,000 for a 1,600 square foot home before those extras.

Most insurers want written confirmation that no live knob and tube remains, from the electrician who did the work, backed by the permit sign-off. Some want photos of the new panel and the disconnected old runs. Ask your agent exactly what the underwriter needs before work starts, so the paperwork at the end matches.

If only part of the house has it, a survey that shows which circuits are affected can keep you from paying to rewire rooms that are already modern. An electrical safety inspection gives you that map.

A full replacement can be done room by room in an occupied home, with each room back on power at the end of the day. Attic runs come first where insulation is packed around them, then the heaviest circuits, then the rest. Planned this way, the house is never without power overnight, and the insurer's deadline can usually be met.

Our knob and tube replacement page covers the process in more detail.

If you are buying an older house, find out about the wiring before you close, not after. A home inspector may flag knob and tube, but an electrician can tell you how much of it is still live, which circuits it feeds and roughly what replacement will cost, which is useful in negotiating the price.

Call your insurer early too. Some will write a policy with a deadline to replace it; others will not write one at all until it is gone. Knowing which before the closing date keeps you from scrambling for coverage in the last week, and it may change how you plan the first renovation.