# Knob-and-Tube Replacement During Renovation in Philadelphia

> Found knob-and-tube in a Philadelphia kitchen, bath or attic remodel? What to settle before walls close, how inspections fit the schedule and what to budget.

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

Service / During a renovation

Replace knob-and-tube that a remodel uncovers while the walls are open, with the electrical permit, rough-in inspection and other trades sequenced around it.

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/) handles knob-and-tube replacement for Philadelphia homeowners who uncover the old wiring partway through a remodel, coordinating licensed and insured electrical contractors with the renovation already underway. Knob-and-tube replacement during renovation is a timing problem as much as a wiring one. The demolition has exposed circuits that would normally take careful fishing to reach, and the insulation and drywall crews are scheduled to cover them. What gets decided in the next few days determines whether the house comes out of the remodel with a clear electrical system or with old circuits sealed behind new walls.

The good news is that an open wall is the cheapest access a rewire ever gets. The bad news is that knob-and-tube found inside one room nearly always serves others, and the renovation contract rarely covers them. This page explains how to handle that gap.

## What happens on the first visit

A visit during a renovation starts with what demolition has exposed. The electrician looks at each run of porcelain knobs and tubes in the open walls, ceilings and floors, notes where splices have been made, and traces which direction each run heads once it leaves the work area. Whether a run is live cannot be settled by looking at it; that comes from the panel and from testing by the electrician. The guide to [active and abandoned knob-and-tube](https://phillyknobandtube.com/guide/active-vs-abandoned-knob-and-tube/) explains how the two are told apart.

The second half of the visit happens outside the renovated rooms. The goal is a circuit map that shows, for every old circuit passing through the open walls, which other outlets and lights depend on it. That map is what lets you decide whether to replace a circuit back to the panel, disconnect it because it is already dead, or leave it running to rooms outside the project with a written note that it remains. The visit also checks the panel for space for new circuits, since a kitchen or bath almost always adds several.

## Where Renovations Expose Old Circuits

Kitchens are the most common place it happens. Removing upper cabinets and plaster from an exterior or party wall often reveals the original wiring, sometimes still feeding a ceiling light or a single receptacle, sometimes cut and capped during an earlier kitchen update. Bathrooms are similar, with the added issue of moisture: older bathrooms may have had knob-and-tube running close to a tub or through a wet wall, and splices made there during later updates are a known weak point.

Attic finishing exposes the top of the house. Knob-and-tube on attic floor joists often feeds the ceiling lights of the floor below and sometimes the switches and outlets in upstairs rooms. Turning that attic into a bedroom or office means floors, insulation and new ceilings over the joists, which would bury those runs for good. Removing a wall, a popular change in narrow rowhouses where owners open the front and middle rooms into one, exposes whatever passed through it, often a vertical run up to the second floor.

Basement finishing deserves its own mention. In many rowhouses the open basement ceiling is where the first-floor circuits run, and it is also the easiest route for future rewiring of the rooms above. A drywall ceiling installed under live knob-and-tube does two things at once: it hides circuits that still need attention, and it closes the access path that would have made replacing them simple. If a basement is about to be finished, the circuits in its ceiling are worth mapping first, even when no other room is being touched, because the cost of replacing them rises sharply once that ceiling is closed.

Floor removal is the quiet case. Lifting old subfloor or tile to level a floor can reveal knob-and-tube running through the joist bays below, feeding the ceiling lights of the room underneath. What all these situations share is that the exposure is temporary. Once the new surfaces go on, the same wiring is as hard to reach as it was before the remodel.

## Coordinating Electrical Work With Other Trades

On a typical renovation the order inside open walls runs: demolition, framing changes, plumbing and HVAC rough-in, electrical rough-in, the electrical rough-in inspection, insulation, then drywall or plaster. Plumbing and duct work usually go first because pipes and ducts are larger and less flexible than cable. The electrical rough-in fits around them, and the inspection has to pass before anything covers it.

Knob-and-tube changes that order in two ways. First, the old circuits have to be dealt with before the new framing and mechanical work disturb them. A plumber cutting a new drain path through a joist bay can damage brittle conductor insulation, and a carpenter sistering joists may need to work around knobs still holding live wire. Identifying which runs are live, and de-energizing or removing the ones being replaced, protects everyone working in the space. Second, the open walls are an opportunity to reach other rooms. A gutted kitchen wall may be the only easy vertical path to a bedroom above, and running a new circuit up through it while it is open can save openings in finished plaster later. The [plaster-wall rewiring](https://phillyknobandtube.com/plaster-wall-knob-and-tube-rewiring/) page explains what those later openings involve when this chance is missed.

Insulation needs its own warning. Many renovations add insulation to exterior walls or the attic, and insulation around live knob-and-tube is a separate concern covered in the guide to [knob-and-tube and insulation](https://phillyknobandtube.com/guide/knob-and-tube-and-insulation/). The simplest rule is that no insulation should go in until the electrical plan for those cavities is settled and the rough-in has passed.

## When Hidden Wiring Expands the Scope

The biggest decision in a renovation discovery is what to do where a knob-and-tube circuit crosses the boundary of the project. There are two basic choices. One is to splice the renovation wiring onto the existing circuit, or to cut the old run at the edge of the work area and connect it to new cable there. The other is to run new circuits from the panel for the renovated rooms and replace each knob-and-tube circuit back to its source, disconnecting the old conductors.

Splicing onto knob-and-tube looks cheaper but carries real costs. The old circuit has no equipment ground, so anything new attached to it is ungrounded too. It was laid out for a few lights and outlets, not for the loads of a modern room. The 2020 National Electrical Code, which Philadelphia applies, requires current protection such as arc-fault devices when certain branch circuits are extended or modified, and every splice has to sit in a junction box that stays accessible after the walls are closed. A buried splice between old and new wire is one of the conditions inspectors and insurers object to most. The guide to [splices and junction boxes](https://phillyknobandtube.com/guide/knob-and-tube-splices-and-junction-boxes/) explains why.

Replacing back to the panel is the cleaner result, and in practice a kitchen or bath needs new dedicated circuits anyway. The harder question is how far to chase the old circuits once they leave the room. If the circuit map shows that one old run feeds the dining room and two upstairs bedrooms, replacing it fully means work in rooms the renovation was not touching. That is where a renovation discovery turns into a [partial replacement](https://phillyknobandtube.com/partial-knob-and-tube-replacement/), with a defined boundary and a written list of what remains, or into a broader conversation about the whole house. Either is reasonable. What causes problems later is a house described as rewired after a remodel when knob-and-tube still feeds half its rooms. In an older house with original trim and ornament outside the work area, the [historic-home replacement](https://phillyknobandtube.com/historic-home-knob-and-tube-replacement/) page covers how to extend the work without damaging finishes.

## Permits, Inspection and Finish Work

Replacing knob-and-tube branch circuits is permitted electrical work in Philadelphia. L&I issues electrical permits, applications go through eCLIPSE, and a licensed electrical contractor must perform the work. Inspections are done by a licensed third-party electrical inspection agency hired by the owner or the owner’s agent. One- and two-family houses with connected load under 200 amps can often use an EZ permit without plans.

Renovations add a second layer. L&I requires a separate Building Permit for many interior and exterior renovations, and most electrical work on a renovation sits alongside one. Whether the scope triggers it is determined by the contractor and noted on the electrical application. If the renovation already has a Building Permit and an electrical permit, discovered knob-and-tube may mean revising the electrical scope rather than starting over, and the electrical contractor handles that.

Timing is the part that most affects the renovation schedule. Rough-in work must be inspected before it is concealed. Where the general contractor needs cable in the walls before the full electrical permit is issued, the City offers a Rough-in Permit for $150 that allows cable to be installed ahead of the full permit; its approval lasts 60 days and the work must not be concealed under it. The permit fee itself is $25 for each $1,000 of estimated electrical construction cost, with a $63 minimum. As an example, a $15,000 electrical scope works out to 15 × $25 = $375, plus the $100 filing fee that counts toward the final fee and small City and state surcharges. The [Philadelphia permit guide](https://phillyknobandtube.com/guide/philadelphia-electrical-permits-for-rewiring/) covers the full schedule, and the [replacement timeline guide](https://phillyknobandtube.com/guide/knob-and-tube-replacement-timeline/) shows how inspections fit around the rest of the work.

## Budgeting for an Active Renovation

A renovation budget usually has a contingency line, and discovered knob-and-tube is exactly what it is for. The cost depends on how many active knob-and-tube circuits pass through the work area, how far they reach beyond it, whether the panel has room for new circuits, how many devices and rooms are involved, and how much finished plaster has to be opened outside the renovated rooms. Open walls cut the access cost that normally dominates a rewire, so replacing circuits that run through the project area costs less now than it will after the walls are closed.

For a sense of scale, limited partial replacement of a few circuits is commonly budgeted at $2,000 to $8,000 as a national range; that figure has not been verified for Philadelphia. A substantial whole-home knob-and-tube replacement in a Philadelphia house is often planned at $9,000 to $25,000, a planning range rather than a quote from Philly Knob & Tube, covering replacement of the active branch circuits but not necessarily restoration, painting, panel or service work. The [cost estimator](https://phillyknobandtube.com/tools/knob-and-tube-cost-estimator/) shows how those drivers interact, and the [rewiring process guide](https://phillyknobandtube.com/guide/knob-and-tube-rewiring-process/) explains each stage of the work.

The schedule cost can be larger than the dollar cost. Every day the drywall crew waits on an unplanned electrical decision is a day the kitchen stays unfinished, so the most useful step is to get the circuit map done as soon as the old wiring appears. Neighborhood pages under [service areas](https://phillyknobandtube.com/service-areas/) describe the housing in each part of the city, the [guide library](https://phillyknobandtube.com/guide/) answers related questions, and the [about](https://phillyknobandtube.com/about/) page explains how the company arranges work. Send photos of the open walls and a description of the renovation through the [contact](https://phillyknobandtube.com/contact/) page to start.

## What's included

- A walk-through of the open rooms to identify exposed knob-and-tube and where each run comes from and goes
- Circuit mapping beyond the renovated rooms to find what else the old circuits feed
- A written choice for each exposed run: replace back to the panel, disconnect as abandoned, or leave outside the scope and document it
- New circuits for the renovated rooms and replacement of the knob-and-tube circuits agreed in scope
- Coordination of the rough-in inspection with the general contractor's insulation and drywall schedule
- The L&I electrical permit and third-party inspections, filed by a licensed electrical contractor
- A record of any knob-and-tube that remains in the rest of the house

## Splicing onto old wiring or replacing back to the panel

|  | Extend or splice onto knob-and-tube | Replace back to the panel |
| --- | --- | --- |
| What it does | Connects new renovation wiring to an existing knob-and-tube circuit | Runs a new circuit from the panel and disconnects the old run |
| Grounding | No equipment ground on the old circuit | Grounded circuit throughout |
| Load | Adds load to a circuit sized for a few lights and outlets | New circuit sized for the room's actual use |
| Code requirements | Extension triggers current protection rules and a junction box that stays accessible | Built to current code from the start |
| Later | Leaves a mixed circuit that someone will have to trace | Clear boundary, documented in the circuit schedule |

## Related resources

- Learn [How Does Knob-and-Tube Rewiring Work?](https://phillyknobandtube.com/guide/knob-and-tube-rewiring-process/)The technical sequence behind a rewire, from tracing which old circuits are live to the moment the last original run is cut loose at the panel and the inspection agency signs off.
- 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.
- 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 [Knob-and-Tube Splices and Junction Boxes](https://phillyknobandtube.com/guide/knob-and-tube-splices-and-junction-boxes/)Original knob-and-tube splices were soldered and left in open air. Many later ones were taped and buried. Here is why the difference matters and what a box is supposed to do.
- Learn [Can knob and tube wiring be covered with insulation?](https://phillyknobandtube.com/guide/knob-and-tube-and-insulation/)Knob and tube was designed to cool itself in open air. Burying it in insulation changes that, and the electrical code treats insulated cavities differently. Here is why, and what to settle before an energy upgrade.
- Decision Guide [How Can You Tell if Knob-and-Tube Wiring Is Active or Abandoned?](https://phillyknobandtube.com/guide/active-vs-abandoned-knob-and-tube/)Live and dead knob-and-tube look identical. Here is how status is actually established, and what a written finding of abandoned wiring needs to contain.

## 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

Kitchen in an old Philadelphia rowhouse with one section of plaster removed to expose studs and the rest of the wall intact

Opened stud bay in a plaster wall with one empty old porcelain knob on the left stud and a new white cable stapled to the right stud into a blue outlet box

Rowhouse living room with furniture under plastic, drop cloths and a zippered plastic dust barrier over the kitchen doorway

Finished kitchen outlet beside a still-open wall section with a new cable stapled to a stud into a blue box

## During a renovation questions

### Can my contractor just connect the new kitchen wiring to the old knob-and-tube?

It is possible in a narrow sense but rarely a good idea. A knob-and-tube circuit has no equipment ground, was sized for light loads, and any connection has to be made in a junction box that stays accessible. Extending it also brings current code requirements into play. A new kitchen needs dedicated circuits regardless, so most renovation plans run new circuits from the panel and disconnect the old run.

### Do I need a new permit if knob-and-tube turns up halfway through a remodel?

Replacing branch wiring is permitted electrical work in Philadelphia, so it needs to be on an electrical permit filed by a licensed electrical contractor. If the renovation already has one, the contractor determines whether the new scope fits it or needs a revision. Minor repairs like swapping a switch may not need a permit; replacing knob-and-tube circuits does not fall in that category.

### Why does the electrician want to look at rooms we are not renovating?

Because the knob-and-tube exposed in an open wall almost always continues somewhere else. A run in a gutted kitchen may feed the dining room outlets and a bedroom ceiling light upstairs. Disconnecting it without mapping where it goes can leave other rooms without power, and replacing it only inside the kitchen walls leaves the rest of that circuit unchanged.

### Can insulation go into the walls before the old wiring is dealt with?

It should wait. Insulation packed around live knob-and-tube changes how the conductors shed heat, and the rough-in inspection has to happen before insulation and drywall cover new wiring anyway. Schedule insulation after the electrical rough-in passes, and make sure any knob-and-tube that stays live is not inside the cavities being insulated.

### How much should I add to a renovation budget for knob-and-tube I just found?

It depends on how far the old circuits reach. Replacing a few circuits is commonly budgeted at $2,000 to $8,000 nationally, a figure not verified for Philadelphia, while a substantial whole-home replacement in a Philadelphia house is often planned at $9,000 to $25,000. Open walls lower the access cost, so a circuit map is the step that turns those ranges into a real number.

## Related services

### Partial replacement

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

### Plaster-wall rewiring

New circuits fished through plaster-and-lath walls with planned, mapped openings and a patching scope agreed before the first cut.

### Historic homes

Replace live knob-and-tube in an older Philadelphia house with a plan that decides, room by room, which period finishes are touched and which are left alone.