# Partial knob and tube replacement in San Francisco

> Partial knob and tube replacement in San Francisco: remaining old circuits replaced, the boundary documented, and a clear answer on partial vs full rewire.

URL: https://fogcitysfknobandtube.com/partial-knob-and-tube-replacement/

**Service**

The circuits still running on knob and tube replaced from the panel out, with a written record of exactly what remains.

Last Updated: October 30, 2026

**Where**

San Francisco and the East Bay: Berkeley, Oakland, Alameda and Piedmont.

**Local rules**

- An electrical permit from DBI before new wiring goes in, then a pre-cover and a final inspection.San Francisco Electrical Code 89.127
- A separate permit for each dwelling unit, except in single-family (R-3) buildings.DBI fee schedule
- Only owner-occupants of a single-family home may pull their own electrical permit.SF Department of Building Inspection
- No insulation around concealed knob and tube without a licensed electrical contractor's certification.California Electrical Code 394.12
- Up to $2,000 toward active knob and tube for income-qualified PG&E customers in an EASE Home project.BayREN

[Fog City SF Knob and Tube](https://fogcitysfknobandtube.com/) manages partial knob and tube replacement in San Francisco and the East Bay: the circuits that still run on knob and tube are replaced from the panel out, while circuits already rewired by earlier work are left in place, and the boundary between the two is written down. Licensed and insured electrical contractors (California C-10) carry out the electrical work.

A partial rewire replaces some of a house’s branch circuits rather than all of them. It fits a familiar San Francisco history: a kitchen and bathroom remodeled decades ago, a new panel at some point, and a handful of bedroom, hall and ceiling-light circuits still on the original wiring. Of the DBI electrical permits filed from January 2016 to October 2026 whose descriptions name knob and tube, 156 also mention a remodel or renovation, which is how many houses ended up half old and half new.

## What happens on the first visit

The first visit finds the boundary. Every circuit is tested and traced from the panel or fuse box, and each one is recorded as fully replaced, still on knob and tube, or mixed, meaning later cable joined to an old run somewhere along the way. Mixed circuits are the reason a partial job cannot be scoped by room. A remodeled bedroom with new outlets may still be fed through an original run in the ceiling, and a hall light on knob and tube may share a neutral with a later circuit.

The visit also checks how each remaining circuit can be reached from the attic, basement or garage, what finishes sit in the way, and whether the panel has space for the replacement circuits. The written scope then lists each circuit to be replaced, each circuit staying, each opening and who closes it.

## Partial vs full rewire: which fits

A partial replacement is the better value when testing shows most circuits already on modern grounded cable and only a few still on knob and tube, with clean boundaries between them. A full rewire is usually better when most circuits are original, when several wiring eras are spliced together, or when the remaining knob and tube runs through rooms that will be opened anyway.

Cost is the deciding detail. A national budgeting range for partial work on several remaining circuits is $2,000 to $10,000; a typical San Francisco range for a whole-house knob and tube replacement in a single-family home is $20,000 to $50,000 or more. Those ranges look far apart, but phased work tends to close the gap. Each phase has its own setup, permit, openings and patching, and the access in a room is paid for twice when a later phase reopens it. If the plan is to replace everything eventually, doing it in three or four separate jobs can approach the cost of one [whole-house rewiring](https://fogcitysfknobandtube.com/whole-house-rewiring/).

Other factors push one way or the other. An attic about to be insulated, a sale, or an insurer asking about any knob and tube rather than active knob and tube all argue for finishing the job. A tight budget, an occupied rental, or remaining circuits that are sound, unburied and correctly protected can argue for a partial scope now, with the rest planned. The [repair or replace guide](https://fogcitysfknobandtube.com/guide/can-knob-and-tube-wiring-be-repaired/) explains when leaving a sound circuit alone is reasonable.

## Replacing a circuit, not an outlet

The unit of a partial replacement is the circuit. A new grounded cable runs from a breaker in the panel to every outlet, switch and light that circuit served, and the old run is disconnected at both ends. Swapping one outlet or one stretch of wire leaves the rest of the circuit on knob and tube, still protected by whatever fuse or breaker it had, and adds a joint between eras where none existed.

New circuits are built to current code. Replaced branch circuits in most living areas need arc-fault protection under California Electrical Code 210.12, with an exception only for short extensions of 6 feet or less that add no outlets. Kitchens, bathrooms, laundry areas and the other listed locations need ground-fault protection, and new receptacles must be tamper-resistant. Every new cable carries an equipment grounding conductor, which is what makes the new three-prong outlets grounded rather than three-prong in appearance; the [grounding page](https://fogcitysfknobandtube.com/ground-outlets-old-house/) covers houses where that is the main goal. The [AFCI and GFCI guide](https://fogcitysfknobandtube.com/guide/afci-gfci-knob-and-tube/) explains what each device protects against.

## Where old meets new: junction boxes and the boundary

Every partial job has a boundary, and the boundary is where problems hide if it is drawn carelessly. Earlier work in some houses joined new cable to old runs inside ceilings and walls, sometimes with no box, sometimes in a box later buried under insulation. Those joints are hard to find and easy to forget.

A clean partial replacement puts the boundary at the panel wherever it can, by giving each replaced circuit its own breaker and its own cable from end to end. Where an old circuit has to stay connected to something, the connection sits in a junction box that can still be reached and is noted in the circuit record. A box that will end up behind closed plaster with no cover access is a sign the boundary is in the wrong place. The [guide to knob and tube mixed with Romex](https://fogcitysfknobandtube.com/guide/knob-and-tube-mixed-with-romex/) describes the hidden-splice and shared-neutral patterns that testing looks for.

## Writing down what stays

The circuit record is the part of a partial job owners most often wish they had. Homeowners report buying houses described as rewired and finding, years later, ceiling fixtures still fed by knob and tube that an earlier job left behind. The record prevents that by naming each replaced circuit, each circuit still on knob and tube and each dead run that was disconnected, and the labeled panel directory matches it.

That record also answers the insurer’s question. Some carriers ask only whether active knob and tube remains, others whether any is present, and a carrier may decide either way. A partial job that replaces every live circuit, with dead runs disconnected at both ends and listed, gives an underwriter facts instead of a guess; an [electrical inspection for insurance](https://fogcitysfknobandtube.com/electrical-inspection-for-insurance/) writes those findings up in the carrier’s terms. Runs that are dead but still in the walls are handled by [knob and tube removal](https://fogcitysfknobandtube.com/knob-and-tube-removal/).

## Permits, phases and access

A partial replacement needs a DBI electrical permit, because replacing a circuit changes existing wiring and falls outside the exemption for like-for-like device swaps. Current DBI fees run $305 for up to 10 outlets and devices with one inspection, and $450 for 11 to 20 with two. The pre-cover inspection happens before any opening is closed; DBI can order concealed, uninspected work exposed at the owner’s expense, so patching waits for it. The [San Francisco permit guide](https://fogcitysfknobandtube.com/guide/san-francisco-electrical-permit/) covers the steps.

Phases work best when each one follows an access event that is happening anyway: a remodel opening a room, a ceiling coming down, an attic being cleared for insulation. The [remodel replacement service](https://fogcitysfknobandtube.com/remodel-knob-and-tube-replacement/) plans circuits around open walls. In plaster rooms, openings are small and placed at boxes and cavity ends, and [plaster-wall rewiring](https://fogcitysfknobandtube.com/plaster-wall-rewiring/) covers the method.

East Bay rules shape partial scopes too. The City of Alameda’s building official states that knob and tube cannot be extended but may be repaired or re-energized, so any added outlet in a knob and tube room becomes a new circuit, and new circuits may need arc-fault protection; the [Alameda page](https://fogcitysfknobandtube.com/service-areas/alameda/) has the details. Oakland requires an electrical permit for rewiring, while its exemption list covers replacing outlets without rewiring, as the [Oakland page](https://fogcitysfknobandtube.com/service-areas/oakland/) explains. The [cost guide](https://fogcitysfknobandtube.com/guide/knob-and-tube-replacement-cost-san-francisco/) puts the partial and whole-house ranges side by side.

**Scope**

## What's included

- A test of every circuit to find which are still live on knob and tube, including ones hidden behind remodeled rooms
- A written scope that names each circuit being replaced and each one staying
- New grounded cable for each replaced circuit, run from the panel to every outlet, switch and light on it
- New boxes, receptacles and switches where the old ones cannot be reused
- Arc-fault, ground-fault and tamper-resistant protection on the new work where the code requires it
- Retired runs disconnected at both ends, removed where reachable, otherwise identified and terminated
- Small openings at boxes and cavity tops and bottoms, with plaster patching as its own itemized line
- DBI permit and inspections, a labeled panel directory and a circuit record showing the remaining boundary

**Choosing the scope**

## Partial replacement, whole-house rewiring or disconnecting the old runs

| Compare | Partial replacement | Whole-house rewiring | Disconnect and remove |
| --- | --- | --- | --- |
| What it changes | The circuits still live on knob and tube | Every old branch circuit, whatever it runs on | Nothing live; dead runs are cut off and taken out |
| Starts from | A test showing most of the house already replaced | A test showing most circuits original or mixed | A test showing runs no longer carry power |
| Knob and tube still live afterwards | None on the replaced circuits; the record lists any kept | None | Unchanged on circuits outside the scope |
| New grounded outlets | On the replaced circuits | Throughout | None |
| Openings | In the rooms the replaced circuits serve | Planned on every floor | Where runs are reachable, usually attic and basement |
| Typical cost | $2,000 to $10,000, a national budgeting range | $20,000 to $50,000 or more, a typical San Francisco range | No published range; depends on access |

**Read next**

## Related resources

- [Decision GuideCan knob and tube wiring be repaired?Where a repair is honest and permitted, where it turns into an extension or a replacement, and how insurers and the insulation rules change the math.](https://fogcitysfknobandtube.com/guide/can-knob-and-tube-wiring-be-repaired/)
- [LearnWhat does it mean when knob and tube is mixed with Romex?Most remodeled older houses have both systems. Where they meet, why those joints matter more than the old wire itself, and how a scope deals with them.](https://fogcitysfknobandtube.com/guide/knob-and-tube-mixed-with-romex/)
- [LearnCan you add GFCI or AFCI protection to knob and tube wiring?What ground-fault and arc-fault devices actually detect, why they behave differently on old circuits, and where they fit next to replacement.](https://fogcitysfknobandtube.com/guide/afci-gfci-knob-and-tube/)
- [Decision GuideCan you replace a light fixture on knob and tube wiring?Why a fixture, fan or switch swap on old wiring so often turns into more, what an electrician looks for at the ceiling, and when the answer is a new circuit.](https://fogcitysfknobandtube.com/guide/knob-and-tube-light-fixture/)
- [Cost GuideHow much does knob and tube replacement cost in San Francisco?The ranges, what moves a house within them, and the parts of the price that come from public figures.](https://fogcitysfknobandtube.com/guide/knob-and-tube-replacement-cost-san-francisco/)

**How a job runs**

## From the first call to the Green Tag.

### First call

Tell us what started this: an insurer's letter, an inspection report, a remodel, an attic you want to insulate.

The age of the house, the number of units and any deadline shape the next step.

### Walk-through

Circuits are tested to separate live knob and tube from abandoned runs, and attic, basement and garage access is checked.

Plaster, trim and finishes are noted, and you get a written scope and price.

### The work

The permit is filed with DBI. New cable is fished along the planned routes and openings are kept small.

The pre-cover inspection happens before anything is closed.

### Patching, inspection and the Green Tag

Once the pre-cover inspection passes, the openings are patched. Plaster patching is included and shown as its own line in the quote.

After the final inspection and the Green Tag, old runs are removed or terminated and the panel directory is updated.

**On the job**

## What this work looks like

An old push-button light switch in a brass cover plate beside a stained wood door frame

A gloved hand holding a yellow voltage tester to cloth-covered wires on porcelain knobs along a basement beam

An open ceiling light box in a plaster ceiling with new white cable inside and the glass shade on a drop cloth below

A receptacle beside the mirror of a small white-tiled bathroom in an older San Francisco flat

**Questions**

## Partial knob and tube replacement: questions

### What does replacing only the remaining knob and tube circuits cost?

A national budgeting range for replacing several remaining knob and tube circuits is $2,000 to $10,000. No published San Francisco figure exists for partial work. The DBI permit is $305 for up to 10 outlets and devices or $450 for 11 to 20, and plaster patching is its own line in the quote.

### How will I know which knob and tube is left after a partial replacement?

From the written circuit record. It names each circuit that was replaced, each circuit still on knob and tube and each dead run that was disconnected, and the labeled panel directory matches it. Keep it with the DBI permit final; insurers, buyers and the next electrician will ask what remains.

### Can I add outlets to a room that is still on knob and tube?

Not by extending the old circuit. Adding an outlet to knob and tube is new wiring, and Alameda's building official states outright that knob and tube cannot be extended. The usual answer is a new grounded circuit from the panel for that room, which is a partial replacement of the circuit that served it.

### Will an insurer accept a house after a partial knob and tube replacement?

It depends on the carrier and on what remains. Some insurers ask only whether active knob and tube is left; others ask about any. A partial job that replaces every live circuit, with the dead runs disconnected and documented, answers the first question. No replacement can promise a carrier's decision.

### Does a partial replacement need its own DBI permit?

Yes. Replacing a circuit changes existing wiring, so it is outside the permit exemption for like-for-like device swaps. The DBI electrical permit covers it, with a pre-cover inspection before openings are closed and a final inspection after. In buildings with several units, each dwelling unit outside an R-3 occupancy needs its own permit.

**Related services**

## Other work on the same wiring

### Whole-house rewiring

Every old branch circuit replaced, new circuits added where the house needs them, and the panel sized for the load.

### Knob and tube removal

Dead and abandoned runs verified, disconnected at both ends, taken out where reachable and recorded, so nobody mistakes them for live wiring later.

### Remodel knob and tube replacement

Old wiring replaced while a kitchen, bath or garage is open, with each circuit followed past the work zone so nothing new is spliced onto old runs.