Knob and tube wiring insurance problems have become one of the most common electrical headaches for San Francisco homeowners, and the reason comes down to the city’s age. According to the San Francisco Planning Department’s Housing Inventory, cited by the Mayor’s Office of Housing and Community Development, almost 77 percent of the city’s housing stock was built before 1950, the exact era when knob and tube wiring was the standard method for running electricity through a home. Walk through the Sunset, Noe Valley, or the Richmond, and you are walking through decades of Victorians, Edwardians, and postwar cottages that were wired long before three-prong outlets, GFCI protection, or modern appliance loads existed.
If your home falls into that 77 percent, there is a good chance an electrician or a home inspector has already mentioned knob and tube wiring to you, maybe during a routine repair, maybe during a home purchase. What often surprises homeowners is that the bigger issue is not a fire, a shock, or a tripped breaker. It is a letter from their insurance company.
What Knob-and-Tube Wiring Actually Is
Knob and tube wiring, often shortened to K&T, was the standard residential wiring method from the 1880s through the 1940s. According to the International Association of Certified Home Inspectors, it consists of individual copper conductors run through open air, supported by porcelain knobs and passed through framing members inside porcelain tubes. There is no ground wire, no shared cable jacket, and no modern insulation. On its own, properly installed knob and tube wiring is not automatically dangerous. The risk comes from age, from insulation that has become brittle and dried out over eight or nine decades, and from years of amateur splices, added circuits, and attic insulation that traps heat around wires that were designed to dissipate it into open air.
That combination, old materials plus decades of small, undocumented changes, is exactly what makes underwriters nervous, and it is why knob and tube wiring insurance questions rarely come up in isolation. They usually surface alongside an old panel, a handful of ungrounded outlets, or a wiring history nobody in the house fully understands.
Why This Hits San Francisco Harder Than Most Cities
Every older American city has some knob and tube wiring left in its housing stock, but San Francisco’s situation is unusual because of how much of the city was built, and largely left alone, before mid-century. Reporting from the San Francisco Chronicle notes that more than 40 percent of the city’s homes were built before 1940, a share driven by the city’s Gold Rush-era growth and decades of slow-moving development since. That is a far higher concentration of pre-war housing than most California metro areas, and it means the knob and tube conversation is not a niche issue here. It is close to a citywide one.
San Francisco also has a large share of multi-unit buildings, and that adds a layer most single-family-home guides do not cover. In a duplex, triplex, or small apartment building, knob and tube wiring is rarely confined to one unit. It is common for the original wiring to have been extended, tapped into, or partially replaced across multiple units over several decades, which means resolving an insurance issue in one unit can require coordinating with other owners, a property manager, or a homeowners association before an electrician can even start the work.
Why Insurance Companies Are Backing Away From Knob-and-Tube Wiring
For years, knob and tube wiring was a conversation between a homeowner and an electrician. Now it is a conversation between a homeowner and an insurance company, and that shift has accelerated quickly. A 2025 ABC7 News investigation found that Bay Area homeowners are increasingly being denied coverage, or having existing policies non-renewed, specifically because their home still has knob and tube wiring. Insurance brokers interviewed for that report described a blunt reality: disclose knob and tube wiring on an application, and many carriers will decline the policy outright, regardless of whether the wiring has ever caused a problem.
This is not happening in isolation. California’s home insurance market has been under enormous strain from wildfire losses, and every carrier still writing policies in the state has become far more selective about the risk it is willing to accept. Knob and tube wiring, once treated as a minor footnote on an inspection report, is now one of the fastest ways to get flagged during underwriting, right alongside older roofs and unpermitted work. Underwriters are not necessarily reacting to a spike in knob and tube related fires. They are reacting to age, to the unknown condition of wiring hidden inside walls for eighty years, and to a market where every avoidable risk gets scrutinized more closely than it used to be.
What Happens When Your Insurer Flags Knob-and-Tube Wiring in San Francisco
The process usually follows a familiar pattern, whether you are a longtime owner renewing a policy or a buyer trying to close escrow. Here is what that typically looks like from application to resolution.
Not every insurer follows this exact sequence, and some will deny coverage outright with no path to a conditional policy at all. But the pattern above is common enough that if you own a pre-1950 San Francisco home, it is worth assuming this conversation is coming rather than being caught off guard by it.
The California FAIR Plan Is a Backstop, Not a Solution
When a standard carrier will not write a policy, the California FAIR Plan is often the option homeowners get pushed toward. The FAIR Plan is a state-created insurer of last resort, and according to the California Department of Insurance, it exists specifically for property owners who cannot find coverage in the traditional market. It is worth understanding what it actually gives you, though. The FAIR Plan’s basic policy covers fire, lightning, and smoke damage, but it does not include theft, liability, water damage, or several other protections a standard homeowners policy provides. Most FAIR Plan customers end up pairing it with a separate difference-in-conditions policy just to get back to something resembling normal coverage, and both together usually cost more than a standard policy would have before the knob and tube wiring became an issue.
In other words, the FAIR Plan can keep a mortgage lender satisfied while a rewiring project is underway, but it is not designed to be a permanent home for a fully insured house. Homeowners who end up here almost always describe it as a bridge, something to get them through the months it takes to complete rewiring, not a long-term insurance strategy.
What an Electrical Inspection Report Needs to Say
Most insurers willing to work with a knob and tube property will ask for a licensed electrician’s inspection report before they will issue or renew a policy. That report typically needs to state clearly whether the knob and tube wiring is still active or has been de-energized, where it is located in the house, and what the plan is to replace or remove it if it is still carrying power.
In practice, homeowners are often surprised by how much of a house is affected once an electrician actually traces the circuits. It is common to find that a previous owner replaced a panel or added a few modern circuits over the decades without ever fully removing the original knob and tube runs feeding the older parts of the home, which is exactly the kind of partial, piecemeal history that shows up during an inspection and raises questions with an underwriter. A thorough inspection also tends to surface issues that have nothing to do with knob and tube wiring directly but still influence how an insurer views the property, things like double-tapped breakers, missing bonding screws in an upgraded panel, or ungrounded two-prong outlets left over from the same era. None of these are unusual to find in a pre-1950 home, but an inspection report that documents them clearly, rather than leaving them for an underwriter to guess about, tends to move an application forward faster.
“If a house still has any live knob and tube wiring, do not just cap it off and hope nobody asks. Insurers want documentation, not assumptions, and a clear inspection report is what actually moves an application forward.”
– Victor, High Voltage Electrical
Partial Rewiring vs. Full Rewiring
Homeowners facing a knob and tube wiring insurance issue generally have two paths. A partial rewire replaces knob and tube circuits in the areas an insurer or inspector specifically flags, often kitchens, bathrooms, and any room with heavy modern electrical use. A full rewire replaces the knob and tube wiring throughout the home and is usually paired with a panel evaluation, since older San Francisco homes with knob and tube wiring frequently have panels that were never sized for today’s electrical loads.
A partial rewire can sometimes satisfy an insurer’s immediate concern for one section of the house, but if the rest of the home still has active knob and tube wiring, that underlying issue has not gone away. It typically resurfaces the next time the policy comes up for renewal, or the next time the home changes hands. A full electrical panel evaluation is usually the more durable fix, and our electrical panel upgrade and rewiring service is built around exactly that kind of whole-house assessment, so the wiring, the panel, and the grounding are all evaluated together instead of one piece at a time.
The scope decision usually comes down to how the home is actually used. A single-family home where the attic and basement are fully accessible is often a more straightforward, lower-cost rewire than a flat inside a Victorian building with plaster walls, no attic access, and a shared electrical chase running between units. In those tighter buildings, an electrician typically has to plan the work around what can be reached without extensive wall or ceiling opening, which is part of why getting a proper on-site assessment matters more than trying to estimate scope from a general online guide.
What This Means if You Are Buying or Selling in San Francisco
San Francisco’s real estate market adds another layer to this. Buyers who order a home inspection are very likely to see knob and tube wiring called out, and as of 2026, California law requires sellers to disclose that a home’s electrical system, including outdated wiring, may make it harder to obtain insurance. That disclosure alone is often what triggers a buyer’s own insurance search to hit a wall before escrow even closes, so getting ahead of it with a professional inspection is usually far less stressful than discovering it mid-transaction. Sellers who can hand a buyer a recent, documented inspection report tend to have a much easier time keeping a deal on track, since it answers the insurance question before it becomes a point of renegotiation.
Getting Ahead of a Knob-and-Tube Insurance Problem
The homeowners who navigate this most smoothly are the ones who do not wait for a non-renewal notice to find out where they stand. A current electrical safety inspection gives you a clear, documented answer about how much knob and tube wiring is left in your home, whether it is live, and what it would take to resolve it, which is exactly what an insurer, and a future buyer, will eventually ask for anyway. It also gives you time to plan the work on your own schedule instead of scrambling to meet a 30 or 60 day replacement window set by an underwriter.
Timing matters here too. Insurance renewals, mortgage refinances, and home sales all tend to be when knob and tube wiring gets flagged, so scheduling an inspection well before any of those events gives you room to plan the work in phases if a full rewire is not something you can take on all at once. Waiting until a non-renewal notice arrives usually means working against a deadline set by someone else, with fewer options and less time to compare quotes.
If you own an older home anywhere in San Francisco and are not sure where your wiring stands, our team offers a full electrical troubleshooting and safety inspection so you have real answers before an insurer forces the issue. You can see the rest of the electrical work we handle across the city on our San Francisco electrician services page.
