# Commercial knob and tube replacement for San Francisco storefront-and-flats buildings

> Knob and tube in San Francisco storefront-and-flats buildings: commercial wiring methods, separate DBI permits, soft-story Tier IV and work around a business.

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

**Service**

Knob and tube replaced in buildings with a shop below and flats above, with the storefront wired to commercial rules and the work planned around both.

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 knob and tube replacement in San Francisco’s mixed-use buildings: the corner and main-street buildings with a shop, cafe or other storefront on the ground floor and flats above. The electrical work is carried out by licensed and insured electrical contractors holding California C-10 licenses. This page covers that one building type; office buildings, warehouses and other all-commercial properties are outside it.

A storefront-and-flats building is two kinds of occupancy under one roof, and San Francisco’s code treats them differently. The flats follow the residential rules that govern any [apartment building rewiring](https://fogcitysfknobandtube.com/apartment-building-rewiring/). The storefront follows the rules for nonresidential space, with a different wiring method, its own permit and a business whose hours shape the schedule. The two share ceilings, risers, a meter bank and often a basement, which is why they are planned together.

## What happens on the first visit

The first visit tests every circuit in the building and records what each one runs on and what it feeds. In mixed-use buildings that second question matters most: the shop’s ceiling is the floor of the flat above, so a lighting run in the storefront ceiling may belong to an upstairs unit, and a back-room outlet may still be on the building’s original fuse box. The test traces those crossings before any scope is written.

The visit also records the meter bank and how the storefront and flats are metered, the basement or rear access, the common stair and hall circuits, any signage or display lighting on the facade, and whether the address appears on DBI’s soft-story list. The result is a written scope and price for the commercial space and for each unit, listing every opening and who closes it, and a permit and scheduling plan. A [knob and tube inspection](https://fogcitysfknobandtube.com/knob-and-tube-inspection/) on its own covers the testing half when no work is planned yet.

## Why the storefront is wired differently

San Francisco’s amendments to the California Electrical Code, operative January 1, 2026, permit nonmetallic sheathed cable in wood-frame multifamily buildings of Types III, IV and V up to six stories, but not in nonresidential occupancies, not in the common areas of R-1 and R-2 buildings of Type IIIA construction, and not above 120 V to ground. In practice the flats can usually be rewired with NM cable, while the storefront’s replacement circuits run in metal-clad cable or in raceway.

Two more amendments apply on the ground floor. Premises wiring less than 8 feet above a walking surface is considered subject to physical damage, and metal-clad cable is not permitted where it is subject to physical damage. A storefront’s back room, a basement storage area or a rear garage is exactly where low runs sit, so those runs are protected or placed in conduit. The difference shows up in the price as well as the method, because raceway generally takes more labor than cable, and where a storefront has a later suspended ceiling below the original one, that space changes where new runs can go.

Protective devices follow the space as well. The California Electrical Code’s dwelling-unit rules for arc-fault and ground-fault protection apply to replaced and extended circuits in the flats, and the protection required in the storefront is set by its own use and confirmed in the permit scope. The [AFCI and GFCI guide](https://fogcitysfknobandtube.com/guide/afci-gfci-knob-and-tube/) explains what each device does.

## One permit for each flat, the shop and the common areas

DBI’s fee schedule requires separate electrical permits for each structure, condominium unit, existing dwelling unit and common area. A two-flat building over a shop usually means a permit for each flat, a permit for the commercial space and, where the stair, hall or garage circuits are in scope, a permit for the common area. Each permit has its own pre-cover inspection before any wall or ceiling closes, its own final inspection and its own Green Tag. San Francisco’s homeowner electrical permit covers only a stand-alone single-family home, so every permit on a mixed-use building is pulled by a licensed contractor. DBI’s PermitSF system now takes no-plan electrical permits for residential and commercial buildings alike.

Current DBI fees for the flats run $305 to $740 per dwelling unit, depending on the count of outlets and devices, and two flats each over 40 devices come to $1,480 in permit fees as illustrative arithmetic. The storefront’s permit falls outside DBI’s residential wiring categories, so its fee is confirmed when the permit is scoped. Scheduling affects inspection cost as well: DBI’s hourly inspection rate is $519, rising to $555 for off-hours work with two- or four-hour minimums, and reinspections cost $259 per half hour. The [permit guide](https://fogcitysfknobandtube.com/guide/san-francisco-electrical-permit/) walks through DBI’s process.

## Working around a business and the people upstairs

Two groups lose power during a mixed-use rewire, and they need it at different times. Residents need evenings and nights; the business needs its trading hours. The schedule sets power-off windows for each unit and for the storefront, and announces them in advance to residents and the business, so both know when circuits will be down. Ceiling routes between the shop and the flats are opened in sections, which limits how much of the storefront is covered at any one time.

Lead-safe work applies to both. DBI presumes buildings built before 1979 contain lead paint unless a certified inspector proves otherwise, and its safety guide calls for at least three business days’ notice to neighbors, a posted 32 by 24 inch sign and dust containment. The EPA requires firms paid to disturb paint in pre-1978 housing to be certified, and electrical work is expressly covered; the [lead and asbestos guide](https://fogcitysfknobandtube.com/guide/lead-and-asbestos-during-rewiring/) covers what that adds. Where flats are rented and a tenant has to leave during the work, the Rent Board rules in the [rental property rewiring guide](https://fogcitysfknobandtube.com/guide/rewiring-a-rental-property-san-francisco/) apply.

## Soft-story retrofits and the ground floor

Storefront buildings are named in San Francisco’s seismic program. DBI’s Mandatory Soft Story Program covers wood-frame buildings of five or more residential units with two or more stories over a soft story, and its property list defines Tier IV as buildings with a Group B or M occupancy on the first story, which is business or mercantile use such as a storefront, and buildings in mapped liquefaction zones. Of the 622 soft-story properties in the Mission, 232 are Tier IV; in the Marina, 151 of 407.

Retrofit work opens the ground story, where the storefront ceiling carries the wiring up into the flats. One San Francisco permit describes having to “remove and relocate wiring and outlets that are in conflict with structural work related to the mandatory soft story retrofit.” The structural work belongs to another trade, but the electrical plan can use those openings, which the [soft-story retrofit and rewiring post](https://fogcitysfknobandtube.com/blog/soft-story-retrofit-and-rewiring/) explains.

## Historic districts, insurance and the East Bay

Interior rewiring needs no historic review: San Francisco’s Planning Code exempts interior alterations from Certificate of Appropriateness review in Article 10 districts. A new conduit, meter or service mast on a facade visible from the street is an exterior change, so in a historic district it is checked with SF Planning per address before the [electrical panel upgrade](https://fogcitysfknobandtube.com/electrical-panel-upgrade/) or service work is scheduled.

Insurance questions on a mixed-use building go to whoever writes the building’s policy, and no insurer rule for knob and tube in these buildings has been published to report here. What a carrier can be given is a written circuit record for the storefront and each unit, and an [electrical inspection for insurance](https://fogcitysfknobandtube.com/electrical-inspection-for-insurance/) documents the building before or after the work; the carrier still decides. In the East Bay, Oakland issues commercial (E) electrical permits for commercial buildings and for residential buildings of three or more units, and requires a lead-based paint permit with a lead hazards work plan when work disturbs paint in a building built before 1978.

## What a mixed-use quote should separate

A mixed-use quote is easiest to compare when the storefront, each flat, the common areas, the service and meters, the PG&E side and the permits each have their own line, with plaster and ceiling patching listed per space. Two bids can differ simply because one prices the storefront in raceway and the other assumes cable, which San Francisco does not permit there. The [rewiring quote checklist](https://fogcitysfknobandtube.com/guide/rewiring-quote-checklist/) lists what to ask for, and the [San Francisco cost guide](https://fogcitysfknobandtube.com/guide/knob-and-tube-replacement-cost-san-francisco/) explains what moves the price.

**Scope**

## What's included

- A test of every circuit in the flats, the storefront and the common areas, recording which run on knob and tube and which feed another part of the building
- A map of where storefront, flat and house circuits share ceilings, risers and the meter bank
- A written scope and price for the commercial space and for each unit, listing every opening and who closes it, with plaster patching as its own line
- A permit plan for every dwelling unit, the commercial space, the common areas and any service work
- Scheduled power-off windows, announced in advance to residents and the business
- Wiring methods chosen for each occupancy: NM cable in the flats where permitted, metal-clad cable or raceway in the storefront
- Old runs disconnected at both ends, removed where reachable, otherwise identified and terminated
- A written circuit record and a labeled panel directory for the storefront and each unit

**Choosing the scope**

## How the storefront differs from the flats above it

| Compare | Storefront (commercial space) | Flats above | Common areas |
| --- | --- | --- | --- |
| Wiring method | Metal-clad cable or raceway; NM cable not permitted in nonresidential spaces | NM cable permitted in most wood-frame buildings up to six stories | NM cable not permitted in common areas of R-1 and R-2 Type IIIA buildings |
| DBI permit | Its own permit; fee confirmed when the permit is scoped | One permit per dwelling unit, $305 to $740 each | Its own permit |
| Homeowner permit possible | No | No; only stand-alone single-family homes qualify | No |
| Who is disrupted | The business, its staff and customers | Residents, often tenants | Everyone using the stair, hall or garage |
| Scheduling | Scheduled, announced power-off windows | Announced power-off windows | Coordinated with both |

**Read next**

## Related resources

- [LearnHow does a San Francisco electrical permit work for rewiring?Who can file, what DBI charges, what each inspection checks, and why a Green Tag on its own does not prove the knob and tube is gone.](https://fogcitysfknobandtube.com/guide/san-francisco-electrical-permit/)
- [Decision GuideWhat does rewiring a rental property in San Francisco involve?The landlord's side of a knob and tube job: permits unit by unit, working around tenants, the Rent Board's relocation rules and what a capital improvement petition can and cannot do.](https://fogcitysfknobandtube.com/guide/rewiring-a-rental-property-san-francisco/)
- [LearnDoes knob and tube wiring have asbestos?What the wiring itself is made of, which materials around it deserve a test before anyone cuts, and how lead-safe rules change the way openings are made and patched.](https://fogcitysfknobandtube.com/guide/lead-and-asbestos-during-rewiring/)
- [Decision GuideWhat should a rewiring quote include?The lines that make two knob and tube rewiring quotes comparable, what each one tells you, and the gaps that turn into surprises later.](https://fogcitysfknobandtube.com/guide/rewiring-quote-checklist/)

**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

Silver metal conduit running along the open ceiling of an empty ground-floor shop

Old porcelain-knob wiring and new metal conduit side by side in the basement under a storefront

A gray breaker panel with metal conduit entering its top in the back room of a small shop

A bright kitchen in a flat above a storefront with drop cloths down during rewiring

**Questions**

## Mixed-use buildings: questions

### Can a storefront below flats be rewired with the same cable as the apartments?

Usually not. San Francisco's amendments to the electrical code do not permit nonmetallic sheathed cable in nonresidential occupancies, so the shop is wired in metal-clad cable or raceway while the flats above can use NM cable where it is permitted. Low runs in a back room or basement also need protection from physical damage.

### Does the shop space need its own electrical permit when the flats above are rewired?

Yes. DBI requires separate electrical permits for each structure, each existing dwelling unit and each common area, and the commercial space takes its own permit, with its fee confirmed when the permit is scoped. A two-flat building over a shop therefore usually means at least three permits, each with its own inspections and Green Tag.

### Can the rewiring happen without closing the business downstairs?

That depends on the building and the scope, and it is settled when the schedule is written. Power-off windows are scheduled and announced in advance to the residents and the business, and ceiling routes from the shop up to the flats are opened in sections rather than all at once. DBI inspections outside normal hours cost $555 an hour with two- or four-hour minimums, against $519 regular, so the schedule weighs that cost.

### Does a building with a shop on the ground floor fall under San Francisco's soft-story program?

It can. DBI's Mandatory Soft Story Program covers wood-frame buildings of five or more residential units with two or more stories over a soft story, and its Tier IV includes buildings with business or mercantile occupancy on the first story. Whether a given address is on the list is shown in DBI's soft-story property data.

### What does knob and tube replacement cost in a mixed-use building?

No published San Francisco price band exists for mixed-use buildings, so the storefront and each flat are priced after testing. The permit side is public: DBI charges $305 to $740 per dwelling unit for residential wiring, plus separate permits for the commercial space and common areas, and inspections beyond those included cost $259 per half hour.

**Related services**

## Other work on the same wiring

### Apartment building rewiring

Knob and tube replaced unit by unit or building-wide, with a permit for each dwelling unit and power-off windows announced to residents.

### Electrical panel upgrade

A fuse box or undersized panel replaced, the service resized when the load calculation calls for it, and PG&E's side coordinated.

### Knob and tube inspection

Every circuit traced and tested, live runs separated from dead ones, and findings that say plainly what was tested and what was only seen.