# Knob-and-Tube Replacement for Philadelphia Duplexes, Triplexes and Fourplexes

> Knob and tube replacement for Philadelphia duplexes, triplexes and fourplexes: unit and common circuits, occupied-unit access, permits and phasing. Plan yours.

URL: https://phillyknobandtube.com/multi-unit-knob-and-tube-replacement/

Service / Two-to-four-unit buildings

Map every unit and the shared circuits, then replace live knob-and-tube in phases the people living there can work around.

Last Updated: October 26, 2026

**2020 NEC** The edition of the National Electrical Code that Philadelphia applies to electrical work

**L&I permit** Pulled by a licensed electrical contractor for rewiring work in the City

**Third-party inspection** Rough-in and final inspections by a licensed electrical inspection agency

[Philly Knob & Tube](https://phillyknobandtube.com/) manages knob-and-tube replacement in Philadelphia duplexes, triplexes and fourplexes, with licensed and insured electrical contractors doing the electrical work. This page is for owners of older two-to-four-unit residential buildings: twins and rowhouses divided into apartments, purpose-built two-flats, and small walk-ups that still carry original wiring in some or all of the units. It does not cover apartment buildings of five or more units or commercial property.

A small multi-unit building raises questions a single-family house does not. The circuits belong to different households and sometimes to nobody in particular. The work happens in homes that people live in. And the permit path can change once a building has more than two units. The sections below take those in the order an owner usually meets them.

## What happens on the first visit

The first visit maps the building, not just one apartment. A licensed electrician starts where the service enters, usually the basement, and records the meters, the panel serving each unit and any house panel that feeds common areas. Each panel’s circuits are then followed into the space they serve. Where a basement ceiling is open, the original runs can often be seen leaving the area of the old service and spreading toward the units above, which helps show which circuits were rerouted to new panels and which simply kept their old wire.

Then the electrician needs to get into each unit. Lights and receptacles in every room are matched to their circuits, and the circuits are sorted into modern, knob-and-tube and mixed. That requires access to occupied apartments, so the visit is planned with the owner in advance: which units, what time, and who will let the electrician in. If one unit cannot be reached, the map for the building is incomplete, and the report should say so rather than guess. The [knob-and-tube inspection](https://phillyknobandtube.com/knob-and-tube-inspection/) page describes the mapping process in more detail.

The visit ends with an outline: which units have live knob-and-tube, which common-area circuits do, which circuits cross between spaces, what the access looks like in each unit, and what that suggests for phasing.

## When Older Multi-Unit Buildings Have Active K&T

A small multi-unit building in Philadelphia may not have started life as one. A house wired with knob-and-tube as a single household may have been divided into apartments decades later, and the conversion often added meters, new panels and a few new circuits while leaving the original branch wiring in place. Purpose-built two-flats and small walk-ups from the knob-and-tube era can have similar layers, with each unit rewired to a different extent over the years as kitchens or bathrooms were redone.

Housing age is part of the context. U.S. Census Bureau data show that 39.9% of Philadelphia’s housing units, about 298,000 of 748,000, were built before 1940. Age alone does not prove any building still has active knob-and-tube, but it explains why owners of older small buildings keep running into it: at a refinance, a change of insurer, a sale, or when a unit’s kitchen is opened up between occupants.

The usual triggers for a multi-unit owner are a little different from a homeowner’s. An insurer asking about the electrical system of a building with several households, a buyer’s inspection on a building being sold, or a contractor finding porcelain knobs behind a wall during a unit renovation can all start the conversation. Homeowners report that insurers ask pointed questions once active knob-and-tube is disclosed; each insurer decides individually, so ask for any requirement in writing. The [homeowners insurance guide](https://phillyknobandtube.com/guide/knob-and-tube-homeowners-insurance/) explains how to handle that request.

## Mapping Each Unit and Shared Circuits

A multi-unit map has to answer two questions for each circuit: is it knob-and-tube, and whose is it? The second question matters more than it sounds.

### Separate meters do not prove the wiring was replaced

Separate meters show that the electrical service was divided so each household pays for its own use. They say nothing about the branch circuits that run from each unit’s panel to its lights and outlets. A converted building can have a bank of meters and new breaker panels in the basement feeding circuits that are still knob-and-tube a few feet past the panel. The [panel upgrade versus knob-and-tube replacement](https://phillyknobandtube.com/guide/panel-upgrade-vs-knob-and-tube-replacement/) guide explains why new service equipment and old branch wiring so often sit side by side.

### Circuits that cross unit lines

When a single-family house was divided, the old circuits did not always follow the new unit boundaries. A circuit can feed outlets in one apartment and a light in another, or run from a first-floor unit’s panel to a hallway fixture. Old wiring can also share a neutral between circuits that now belong to different panels, which creates a hazard that is not visible from any outlet. The guide to [shared neutrals in old house wiring](https://phillyknobandtube.com/guide/shared-neutrals-in-old-house-wiring/) explains why that condition has to be found before circuits are separated. Mixed circuits, part modern and part knob-and-tube, are covered in the guide to [mixed knob-and-tube and modern wiring](https://phillyknobandtube.com/guide/mixed-knob-and-tube-and-modern-wiring/).

### Common-area circuits

Hallway and stair lighting, basement lights and outlets, exterior lights at entrances, and the circuit serving a shared laundry are often on a house panel paid for by the owner. In an older building those common circuits can be the ones left alone longest, since no single household’s renovation ever touched them. They get their own section of the map and usually their own phase of the work.

## How Resident Access and Planned Interruptions Work

Replacing branch wiring in a multi-unit building means working inside homes that people live in. The electrical plan has to be built around that, not the other way around.

Access starts with notice. The owner arranges entry to each unit according to the lease and applicable Philadelphia and Pennsylvania rules, and the phasing plan should give enough lead time to do that. Useful notice tells the people living in each unit which days work will happen in their space, which rooms are affected, roughly when power will be off and what they should move away from walls. The guide to [living at home during knob-and-tube rewiring](https://phillyknobandtube.com/guide/living-at-home-during-knob-and-tube-rewiring/) covers preparation from an occupant’s side and is worth sharing with each household.

Planned interruptions are usually shorter than people expect. During most of the work, only the circuits being replaced are off, and the rest of the unit keeps power. Full outages to a unit are generally limited to the time needed to connect new circuits at its panel. Common-area work can affect everyone at once, so stair lighting and hallway circuits are often scheduled for times when the building is quieter, with temporary lighting where the stairs would otherwise be dark.

Openings in plaster are made in occupied rooms, so dust control and covering of furnishings belong in the plan. If an older building may contain asbestos-bearing materials around the old wiring or in plaster, the [asbestos and old house rewiring](https://phillyknobandtube.com/guide/asbestos-and-old-house-rewiring/) guide explains why that question is settled before openings start.

## Permits and Inspections for Two-to-Four-Unit Buildings

All electrical work in Philadelphia is done by a licensed electrical contractor, under an electrical permit issued by the Department of Licenses and Inspections, and inspected by a licensed third-party electrical inspection agency that the owner or owner’s agent hires. That much is the same as for a house. What changes with the number of units is the path the application takes.

L&I’s eCLIPSE system routes permits for one- and two-family dwellings to its Residential path and permits for other buildings to its Commercial path. A duplex therefore usually starts on the Residential side, while a triplex or fourplex goes through Commercial. The EZ electrical permit, which needs no plans, is available for alterations on one-or-two-family dwellings with a connected load under 200 amps and equipment rated 600 volts or less. A duplex rewire may fit that description; a three- or four-unit building does not.

That does not mean every triplex rewire needs a full set of drawings. Whether plans are required depends on the building and the scope, and the licensed contractor determines it when preparing the application. One rule is fixed: plans are always required when a building other than a one-or-two-family dwelling is undergoing a change in occupancy classification, for example when a unit count changes as part of the project. If the knob-and-tube work is tied to that kind of change, expect the permit to take longer.

Inspections follow the work. Rough-in wiring has to be inspected before it is covered, so in a phased project each unit’s open walls wait for the inspection agency before they can be closed. A separate Building Permit may also be needed for renovation work, and the contractor determines whether the scope triggers one. The guide to [Philadelphia electrical permits for rewiring](https://phillyknobandtube.com/guide/philadelphia-electrical-permits-for-rewiring/) sets out fees and steps, and the [final inspection guide](https://phillyknobandtube.com/guide/final-inspection-after-knob-and-tube-rewiring-philadelphia/) covers what closes a permit.

## Routing New Circuits Between Floors

In a single house, a new cable can climb from the basement to the top floor through any convenient wall. In a building with stacked units, that same route passes through someone else’s home. Each unit’s new circuits should start at that unit’s own panel and stay within its own space wherever possible, so that a future outage, repair or panel change in one apartment does not reach into another.

That makes routing in a multi-unit building more constrained. A second-floor unit whose panel sits in the basement needs a feeder or a protected pathway up through the first-floor unit, and branch circuits for an upper unit sometimes have to come down from an attic rather than up from the basement. Where a building has a shared stair hall, the hall walls can offer a route that disturbs no apartment, but they also carry the common lighting and may have finishes the owner wants preserved.

Floors and walls between units may also be part of a fire-resistance-rated separation, depending on how the building was converted and approved. The electrical code requires openings made through rated walls and floors to be firestopped so the separation keeps working, and the inspection agency looks at those penetrations during rough-in. The contractor’s plan should say where new cable passes between units and how those openings are closed.

Panel space is the other routing question. Separating shared circuits and adding the receptacle circuits a modern kitchen needs can fill a small unit panel. Where a unit panel has no room, the plan has to address it within the knob-and-tube scope, and if the service itself must change, a separate PECO application may be involved. A panel change on its own does not replace any branch wiring, so it is a supporting step, not the project.

## Phasing the Work Unit by Unit

Most occupied buildings are rewired in phases. The comparison table further down this page sets out the three common approaches. In practice the plan is set by the circuit map: units whose circuits stay within their own walls can be done in any order, while circuits that cross units or feed common areas set the sequence.

A typical phased plan starts with the common-area circuits and any cross-unit circuits, because separating those makes every later unit simpler. Each unit then follows as its own phase, with its own outage windows, openings, rough-in inspection and restoration. A vacant unit is the easiest place to start, but only after the map confirms that rewiring it will not strand part of a shared circuit.

Phasing changes the total schedule, not just the order. Each phase carries its own setup, inspection visit and restoration, so a building done in four phases takes longer overall than one done at once. The [knob-and-tube replacement timeline](https://phillyknobandtube.com/guide/knob-and-tube-replacement-timeline/) guide explains what drives duration on a single home; in a multi-unit building, add the time between phases that access scheduling requires.

## Replacement Scope, Restoration and Written Quotes

The scope for each unit looks much like a [whole-home knob-and-tube rewiring](https://phillyknobandtube.com/whole-home-knob-and-tube-rewiring/) of a small house: new branch circuits replacing the live knob-and-tube, new boxes where old ones cannot be reused, connections and labels at the unit’s panel, and disconnection of the old runs. Where only some circuits in a unit remain on knob-and-tube, the unit’s scope is closer to a [partial knob-and-tube replacement](https://phillyknobandtube.com/partial-knob-and-tube-replacement/), and the circuits that stay must be listed.

There is no published price for multi-unit knob-and-tube work in Philadelphia. The planning range for a single house, $9,000 to $25,000 for a substantial whole-home replacement, cannot be multiplied by the number of units, because shared routes, common circuits, occupied-unit protection and the permit path change the total in ways a multiplier hides. The [Philadelphia cost guide](https://phillyknobandtube.com/guide/knob-and-tube-replacement-cost-philadelphia/) explains the drivers and the L&I permit fee arithmetic. In a multi-unit building the drivers that tend to matter most are the number of live circuits per unit, whether a basement gives open routes to the floors above, the condition of plaster in each unit, how many phases the occupancy requires, and whether any unit panel lacks space for the new circuits.

Restoration deserves its own line in each unit’s scope. Openings in an occupied apartment have to be closed, patched and usually painted before the household gets the room back, and the quote should say who does that and to what finish. Ask for a quote that breaks the work out by unit and by common area, names each planned outage window, and states what is excluded. The guide to [comparing knob-and-tube rewiring quotes](https://phillyknobandtube.com/guide/comparing-knob-and-tube-rewiring-quotes/) lists the lines that should appear, and the printable quote comparison checklist on the [resources page](https://phillyknobandtube.com/resources/) helps put two bids side by side.

## Records to Keep for the Building

A multi-unit owner will be asked about the wiring again: by an insurer at renewal, by a lender, by a buyer’s inspector, or by the next electrician. The records that answer those questions are easiest to collect while the work is happening.

Keep, for each phase, the permit number, the inspection agency’s rough-in and final reports, and the contractor’s written scope. Keep a circuit map for each unit and for the common-area panel, with the panel directories updated to match. Ask for photographs of new wiring in open walls and ceilings before they are closed, labeled by unit and room. Keep a written list of any knob-and-tube that remains in the building, with its location, so no one later describes the building as fully rewired when it is not. A copy of the notices given to each household about access and outages is worth filing with the rest. The [records post on the blog](https://phillyknobandtube.com/blog/organizing-rewire-records-for-a-home-sale/) explains how to organize these so they are useful years later.

To start with a building-wide map, [request an estimate](https://phillyknobandtube.com/contact/) and say how many units the building has and which are occupied. You can also see which [Philadelphia neighborhoods](https://phillyknobandtube.com/service-areas/) are covered, or browse the [guides](https://phillyknobandtube.com/guide/) for the questions that come before a quote.

## What's included

- A circuit map for each unit and for the house or common-area circuits, showing what is live knob-and-tube
- Identification of circuits that cross unit boundaries or feed shared spaces from a unit panel
- A phasing plan that groups work by unit and by common area, with planned outage windows
- New branch circuits for the knob-and-tube in scope, connected and labeled at the correct panel
- Disconnection of replaced knob-and-tube at both ends
- Electrical permit through the correct eCLIPSE path and the inspections each phase requires
- A written list, per unit, of circuits replaced and any that remain

## Phasing a two-to-four-unit knob-and-tube replacement

|  | All units at once | Unit by unit | Turnover-driven |
| --- | --- | --- | --- |
| How it runs | Every unit and the common areas in one permitted project | One unit or one floor at a time, common areas in their own phase | Each unit is rewired when it is vacant between occupants |
| Disruption | Concentrated; every household is affected during the same weeks | Spread out; one household at a time | Minimal for occupied units, but the building stays mixed for longer |
| Permits | Can be one permit for the building scope | One permit or several, depending on how the contractor structures the work | A separate permit each time a unit is done |
| Shared circuits | Resolved in one pass | Need a plan so a circuit crossing units is not left half done | Hardest to resolve; cross-unit circuits wait for both units |
| Fits when | The building is vacant or every household can be relocated briefly | The building is occupied and the owner wants a defined finish | Insurance or sale pressure is low and units turn over regularly |

## Related resources

- Learn [Which electrical permits does Philadelphia require for rewiring?](https://phillyknobandtube.com/guide/philadelphia-electrical-permits-for-rewiring/)How L&I's electrical permit works for a knob and tube replacement: who files it, which review path a house falls into, how the fee is calculated and what you should hold when the job closes.
- Cost Guide [How Much Does Knob-and-Tube Replacement Cost in Philadelphia?](https://phillyknobandtube.com/guide/knob-and-tube-replacement-cost-philadelphia/)A planning range for whole-home work, a national range for limited jobs, Philadelphia's published permit fees, and the parts of a price that only a property-specific scope can answer.
- Learn [How Long Does Knob-and-Tube Replacement Take?](https://phillyknobandtube.com/guide/knob-and-tube-replacement-timeline/)There is no standard number of days for a rewire. Here is what actually controls the calendar, where the waiting happens, and how phasing trades speed for livability.
- Learn [Shared Neutrals in Old House Wiring: Why They Matter](https://phillyknobandtube.com/guide/shared-neutrals-in-old-house-wiring/)In knob-and-tube houses the return path of a circuit often wanders away from its hot conductor or serves more than one circuit. That hidden routing is why some upgrades trip, and why partial rewiring needs a neutral map.
- Decision Guide [Can You Live at Home During Knob-and-Tube Rewiring?](https://phillyknobandtube.com/guide/living-at-home-during-knob-and-tube-rewiring/)Many households stay put through a rewire, and some should not. What the days actually feel like, which parts of the house go dark and when, and how phasing changes the answer.
- Learn [How Does Knob-and-Tube Wiring Affect Homeowners Insurance?](https://phillyknobandtube.com/guide/knob-and-tube-homeowners-insurance/)Why carriers ask about original wiring, the moments the question comes up, what an electrician's findings can answer for an underwriter, and the parts of the outcome a homeowner can actually influence.
- Decision Guide [How to compare knob and tube rewiring quotes](https://phillyknobandtube.com/guide/comparing-knob-and-tube-rewiring-quotes/)Two rewiring quotes for the same house can differ by thousands because they describe different jobs. Here is how to put them on the same footing before price decides anything.

## What a Replacement Involves

1. Survey Document the property, inspect visible routes, and map what appears to be active.
2. Define Agree on exactly which circuits, access openings and associated repairs belong in the scope.
3. Replace Install the planned replacement wiring through accessible routes and necessary openings.
4. Close out Complete required inspections and document the electrical scope actually performed.

## What this work looks like

Stair landing in a converted Philadelphia rowhouse with a turned-wood banister, two unit doors and a small access opening over a drop cloth

Three closed breaker panels side by side on a backboard in the basement of a converted rowhouse, with cables rising into the joists

Unit door at the top of a stair with the handrail wrapped in plastic and brown paper taped to the floor

Upstairs hallway between two apartment doors with a closed flush-mounted electrical panel and a drop cloth

## Two-to-four-unit buildings questions

### Each unit in my building has its own meter. Does that mean the knob-and-tube is gone?

No. Separate meters and unit panels show that the service was divided, not that the branch circuits were replaced. A building can be split into metered units with new panels while the original knob-and-tube still runs from those panels to lights and outlets. Only a circuit-by-circuit map of each unit answers the question.

### Is a triplex permitted the same way as a single-family rewire in Philadelphia?

Not exactly. L&I's eCLIPSE system routes permits for one- and two-family dwellings to the Residential path and other buildings, including three- and four-unit buildings, to the Commercial path. The no-plan EZ electrical permit is limited to one-or-two-family dwellings under 200 amps, so a triplex follows a different process. The licensed contractor determines which applies.

### How long will each unit be without power during the work?

Usually only the circuits being worked on are off, for part of a working day, and full outages are reserved for panel connections. The exact windows depend on how many circuits a unit has and how they are reached. A good phasing plan lists the planned outages per unit so the owner can give the people living there notice.

### Can I rewire only the vacant unit and leave the others for later?

Yes, as long as the circuit map shows which circuits belong only to that unit. Problems come from circuits that cross unit lines or feed a shared hallway, because rewiring one side can leave the other half on old wire. Those shared circuits need a plan before the vacant unit is closed up.

### Does the $9,000 to $25,000 Philadelphia range apply per unit?

No. That range is a planning figure for a substantial whole-home replacement in a single Philadelphia house. It cannot be multiplied by the number of units, because shared routes, common-area circuits, access to occupied units and the permit path all change the arithmetic. A multi-unit building needs its own quote from its own circuit map.

## Related services

### Inspection and circuit mapping

A licensed electrician traces which knob-and-tube circuits are still live, what they feed and where they connect, so any replacement is scoped from facts.

### Whole-home rewiring

Replace every active knob-and-tube branch circuit in the house, with the permit, inspections and a written record of what changed.

### Partial replacement

Replace the specific knob-and-tube circuits that matter now, disconnect them properly and write down exactly which ones remain.