Yes. Knob and tube wiring that was legal when it was installed and has been maintained is still legal in California and in San Francisco, and no state or city rule orders it removed by a deadline. The California Electrical Code still contains Article 394 for it. What the rules restrict is extending it, covering it with insulation and leaving abandoned runs unidentified.
Fog City SF Knob and Tube manages knob and tube replacement in San Francisco and the East Bay, with the electrical work carried out by licensed and insured California C-10 electrical contractors, and each scope is written against the code that applies at the address. This guide sets out what that code says about existing wiring, where it draws lines, and why “legal” and “insurable” are not the same answer. If you are ready to plan work, start with knob and tube replacement.
Which code applies
California does not adopt the National Electrical Code directly. It adopts the California Electrical Code, which is the NEC plus state amendments. The current edition, effective January 1, 2026, is the 2025 California Electrical Code, based on the 2023 NEC. Cities can then add local amendments.
San Francisco did that in Ordinance 228-25, which repealed the 2022 San Francisco Electrical Code and adopted the 2025 California Electrical Code with local amendments, operative January 1, 2026. The local amendments change service-entrance wiring methods, where nonmetallic cable may run in some multifamily buildings, and how low wiring in garages is treated, but they make no amendment to Article 394. So for knob and tube itself, the state article governs in San Francisco unchanged. When people search for “knob and tube NEC”, this is the chain they are asking about: the NEC article becomes California law through the state code, and San Francisco’s version is the state’s.
What “legal” means for wiring already in the walls
The San Francisco Electrical Code says existing wiring need not be altered if it was legal when installed and has been maintained. That is the rule behind the question. It does not say knob and tube is approved forever regardless of condition; it says the code does not make you replace a lawful, maintained installation just because the rules for new work have moved on.
“Maintained” carries weight. An electrical code assessment compares what is in the house with what the code allowed and requires. For knob and tube, an electrician looks at whether the runs are still supported on their knobs and tubes, whether the insulation is intact, whether fuses or breakers match the wire, whether later splices sit in boxes, and whether anything has been extended or buried. Wiring that has been overfused, tapped with unboxed splices or packed in insulation is no longer the installation that was legal when it went in. The knob and tube danger guide explains why those changes are where the hazard sits.
Where the code draws lines
Extending it
Any new wiring, alteration, extension or addition needs a DBI electrical permit, and new work is built to the current code. San Francisco’s permit exemptions cover like-for-like replacement of devices, fuses and breakers only where no change in existing wiring is involved. Adding an outlet, a fixture or a dedicated appliance circuit is a change. The City of Alameda’s Building Official puts it in one line: knob and tube “cannot be extended,” though existing wiring may be repaired or re-energized. San Francisco’s code does not phrase it the same way, but the effect is similar: the added load goes on a new circuit, with a ground wire and arc-fault protection where CEC 210.12 requires it.
Covering it with insulation
Article 394.12 bars concealed knob and tube in hollow spaces of walls, ceilings and attics where loose, rolled or foamed-in-place insulation envelops the conductors. California’s exception allows insulation only when a California-licensed electrical contractor surveys the wiring and certifies it is in good condition, with no deterioration, improper overcurrent protection, or improper connections or splices; the certification is filed with the building department and a copy goes to the owner; caution notices in English and Spanish are posted at accessible insulated areas; and the insulation is noncombustible and not electrically conductive. The attic insulation service covers both routes: certification or rewiring first.
Leaving dead runs behind
San Francisco’s code requires unused conductors and cables to be either removed or suitably identified and terminated in an approved manner. A run that has simply been cut at the fuse box and left loose in a wall does not meet that. The active vs abandoned guide explains how retired runs should be handled and documented.
Building the replacement
Once a circuit is replaced, the new work meets the current code in full. Replaced or extended branch circuits serving most living areas need arc-fault protection under CEC 210.12, the locations CEC 210.8 lists need ground-fault protection, and new receptacles must be tamper-resistant under CEC 406.12. The new work also gets a pre-cover inspection before walls close and a final inspection before DBI issues the Green Tag; the San Francisco electrical permit guide walks through that sequence.
Does knob and tube have to be replaced?
Not by the code alone. These are what usually turn it into a project:
- An insurer. Thirty San Francisco electrical permits that name knob and tube, filed from January 2016 to October 2026, cite an insurer in their descriptions. Carriers set their own rules; the California insurance guide covers what they ask for.
- A sale. Since January 1, 2026, California Civil Code 1102.6(i) requires sellers or their agents to give buyers a statement advising an electrical inspection. It does not require replacement; the selling guide covers how it plays out.
- A remodel. Opening walls for a kitchen or bath brings new wiring, which cannot simply be spliced onto old runs. Remodel knob and tube replacement covers that case.
- Insulation. Weatherization over live knob and tube needs the certification route or rewiring first.
- Condition. An assessment that finds damage, overfusing or buried splices.
How East Bay cities differ
The state code applies everywhere in California, but local rules shape what a project has to include.
- Berkeley turns the insulation exception into a named city form, the Knob-and-Tube Wiring Safety Report, which an electrician signs and which is posted in the attic before inspection. Berkeley’s time-of-sale energy ordinance also lists knob and tube replacement with four 240-volt receptacles as a six-credit upgrade. See Berkeley.
- Oakland allows a fuse box or subpanel in a clothes closet, and service equipment in a “dog-house,” to be maintained and repaired but not altered, and counts adding a circuit or wiring as an alteration. See Oakland.
- Alameda states that knob and tube cannot be extended but may be repaired or re-energized. See Alameda.
- Piedmont’s local amendments require a 30-amp 240-volt laundry circuit and a 50-amp 240-volt cooking circuit where more than half of a dwelling’s 120/240-volt wiring is replaced, so a whole-house rewire there adds those circuits. See Piedmont.
For Albany, El Cerrito and Richmond, no city-specific knob and tube rule turned up, and local requirements are confirmed per address with each building department.
Who may legally do the work
In San Francisco, a contractor applying for an electrical permit must hold one of the license classifications DBI lists, with the C-10 electrical license covering any electrical work. Under California Labor Code 108, people working as electricians for a C-10 contractor must hold state electrician certification. An owner may take out a homeowner electrical permit only for a stand-alone single-family home that is their primary residence and must do the work personally; LLCs are not eligible. The can I replace knob and tube myself guide covers that route honestly.
Need to know where your house stands?
A walk-through tests each circuit, notes what was extended, overfused or insulated, and tells you plainly what the code and your insurer are likely to care about.
Legal, insurable and safe are three questions
A house can meet the existing-wiring rule and still be hard to insure, because carriers do not underwrite to the electrical code. It can also be lawful on paper and unsafe in practice, if a hidden splice is overheating. The code answers the first question, the carrier the second, and only testing the third. A knob and tube inspection answers the third and gives you a written record for the other two.
For the rules at your address, call (628) 296-7628 or request an estimate.