Everything You Need to Know About Knob and Tube Wiring From Detection to Remediation
- Ethan Bixler
- Sep 25
- 31 min read
Updated: 2 days ago
So, you think you have found knob and tube wiring in your home? Now what?
Frustrated by a seemingly comprehensive guide to knob and tube wiring we set out to compile a guide that covers all aspects. We have linked our table of contents to allow you to jump to the section of your choice. We hope this will inform and assist those faced with the possibility of knob and tube wiring in their home.
Table of Contents
What is knob and tube wiring - a brief introduction
Knob and tube wiring is an early method of electrical distribution that was commonly used in homes built between the 1880s and the 1940s. You’ll notice its distinctive style—individual wires run through ceramic tubes (the “knobs” and “tubes” in the name) and are supported along their runs by porcelain insulators.
What are the Differences Between Knob & Tube and Current Wiring Systems?
While state of the art in its inception, like everything else, it has suffered from the impacts of time and evolution shifting it from desirable to dangerous over the past century. It is quite a testament to its sustainability that at 75+ years old it is still found operational in many homes across the country. The table below outlines the fundamental differences between modern wiring and K&T
Feature | Knob and Tube (K&T) Wiring | Modern Grounded Wiring (e.g., Romex) |
Era of Common Use | Late 1880s to 1940s (North America) | Mid-20th century to Present |
Grounding Conductor | Absent (Two-wire system: hot and neutral only) | Present (Dedicated ground wire for safety) |
Conductor Arrangement | Single insulated conductors run separately, often 4-6 inches apart | Hot, neutral, and ground conductors bundled within a single plastic sheathing |
Insulation Material | Rubber-saturated cloth or early rubber (prone to degradation, brittleness) | Thermoplastic (PVC) or cross-linked polyethylene (XLPE) (more durable, less prone to degradation) |
Heat Dissipation | Relied on free air circulation (suspended wires) | Relies on insulation rating; heat trapped when bundled |
Splices/Connections | Twisted, soldered, taped; often visible and not enclosed in boxes | Enclosed within approved electrical junction boxes |
Electrical Load Capacity | Designed for minimal loads (pre-TV, computers); easily overloaded today | Designed for modern, higher electrical loads |
Fire Hazard Risk | High (due to insulation deterioration, overloading, improper modifications) | Lower (due to modern insulation, grounding, overcurrent protection) |
Shock Hazard Risk | High (due to lack of grounding) | Lower (due to grounding and GFCI protection) |
Code Compliance | Obsolete; permitted to remain only if in "good condition" and undisturbed | Fully compliant with current National Electrical Code (NEC) standards |
What Are the Dangers of Knob and Tube Wiring
Lack of Grounding
This is the most critical inherent limitation. Without a ground wire, there is no safe, low-resistance path for fault currents to return to the source in the event of a short circuit or electrical surge. This significantly increases the risk of electric shocks to occupants, damage to sensitive modern electronic equipment, and potential fire hazards. Consequently, three-pronged appliances, which require a ground for safe operation, cannot be properly serviced by ungrounded K&T outlets.
Insulation Deterioration
The original rubber or asphalt-saturated cotton cloth insulation used on K&T wires was not designed for longevity comparable to modern thermoplastic insulation. Over decades of service (80-100+ years), this insulation becomes dry, brittle, cracks, and can even disintegrate. This exposes the live copper conductors, dramatically increasing the risk of short circuits, arcing, and electrical fires if the exposed wire contacts other conductors, metal, or combustible materials. Some early insulation materials also contained additives that could oxidize the copper wire itself.
Improper Modifications ("The Frankenstein Factor")
This is frequently cited as arguably the single greatest real-world danger associated with K&T wiring. Over the many decades since its installation, homes with K&T have often undergone amateur repairs or DIY modifications by unqualified individuals. The most common hazardous alteration involves incorrectly splicing modern, plastic-sheathed (Romex) wiring directly onto K&T conductors, frequently using inadequate methods like electrical tape and failing to enclose the splice within a protective junction box. These amateur splices are notorious points of failure, prone to overheating and igniting fires within concealed wall cavities.
Overloaded Circuits
K&T wiring systems were designed for the minimal electrical loads prevalent in the early 20th century, a time long before the advent of televisions, computers, air conditioners, microwaves, and dozens of other high-powered appliances that are now commonplace. As modern households demand significantly more power, these outdated systems are frequently overloaded, leading to common issues such as frequent tripped circuit breakers or blown fuses, persistent overheating of wires, flickering lights, scorch marks on outlets, and a substantially increased risk of electrical fires.
Building Insulation Interference
A critical safety concern, officially recognized by the National Electrical Code (NEC) through an amendment in 1987, is the prohibition of placing building insulation in direct contact with knob-and-tube wiring. K&T's design relies on free air circulation for effective heat dissipation. When insulation (especially loose-fill or rolled thermal insulation) is laid over or around K&T wires, it traps heat, causing the conductors to overheat beyond their safe operating temperatures, which presents a significant fire hazard. Foam insulation is specifically prohibited for use with K&T wiring.
Physical Damage and Accessibility
K&T wiring was originally suspended away from structural components (a minimum of one inch prescribed by the NEC), rather than being tightly secured. Over time, wires can stretch, sag, or become damaged by rodents chewing on insulation, or through accidental physical abuse during renovations or storage in accessible areas like basements. The brittle nature of aged insulation also means that bending the wires can easily cause it to crack and peel away. Furthermore, because much of K&T wiring is concealed behind walls or ceilings, identifying these problems can be difficult, allowing issues to go unnoticed until they lead to significant damage or hazards.
Insurance Challenges
Due to the heightened fire and electrical shock risks associated with K&T wiring, many homeowners insurance companies are reluctant to provide coverage for properties that still utilize it. Insurers may outright refuse policies, impose steep premiums, or mandate immediate replacement or significant upgrades as a condition for coverage. This significantly complicates property transactions and can make it more costly and stressful to maintain home insurance.
Cumulative Age and Modernization Risks
The cumulative effect of age and modernization on K&T safety is a critical consideration. While K&T wiring may not have been inherently dangerous when correctly installed, its longevity in practical application almost guarantees it has become compromised. The dangers observed today are direct consequences of its age, the introduction of modern elements it was never designed to accommodate, and subsequent, often unrecorded, modifications. For example, the 1987 NEC amendment prohibiting insulation over K&T illustrates how modern building practices, such as insulation for energy efficiency, can inadvertently create severe hazards when combined with legacy electrical systems. This highlights that safety assessments for historical infrastructure must consider not only original design flaws but also how external factors compound existing risks.
Concealment and Inspection Difficulties
Furthermore, the physical integration of K&T into modern building structures often transforms potential, visible issues into hidden, escalating dangers. While original K&T installations featured visible connections, much of this wiring is now concealed behind walls or ceilings, making problem identification difficult. This concealment means that issues like damaged insulation, overloaded circuits, or improper modifications can go unnoticed until they cause significant damage or present an immediate hazard. This situation has significant ramifications for home inspections, often requiring more invasive or specialized diagnostic techniques to truly assess safety, which adds to the cost and complexity of dealing with K&T.
How to Recognize Knob-and-Tube Wiring’s Presence in Your Home Both Past and Present
What year was your house built?
This should be the starting point for everyone, as if your house was built after 1950, it’s unlikely to have knob-and-tube wiring, which was prevalent until that time.
What to Look for in Your Basement
Look Between the Floor Joists: Your home's floor joists are the large, parallel wooden beams that support the floor above. This is where knob and tube wiring is most visible.
Look for the “Tubes".
When the electrical wires need to pass through a joist, they are protected by a white, porcelain tube. You will see holes drilled through the joists with these porcelain tubes inserted, and the wires running through the center of the tubes. This is a definitive sign of knob and tube wiring.
Look for the "Knobs”
When the wires run parallel to the joists, they are held in place by white, porcelain "knobs." The wires are wrapped around these knobs to keep them securely elevated from the wood framing.
If Present Test Wires With a Non-Contact Voltage Tester to Verify if it is Still Live
It is a good idea to spend the 15 to $20 on a non-contact voltage tester as this will allow you to see if we determine whether the knob into wiring is live or not. Please see our video on how to properly use a non-contact voltage tester
What to Look for in Your Attic
After you’ve inspected the basement, your attic is the next essential place to check. The process is similar, but instead of looking up at the ceiling joists, you will be looking down at the attic floor joists at your feet.
Here are a few specific things to look for in the attic:
Locate the "Knobs" and "Tubes"
Just as in the basement, scan the wooden joists for the tell-tale white porcelain knobs and tubes. The tubes will pass through the joists, while the knobs will be used to secure wires running parallel to them.
Inspect Around Insulation:
Is the floor of your attic insulated? If so, you will need to carefully move some of the insulation aside to see the wiring and joists below. This is a critical safety check. Knob and tube wiring was designed to be suspended in open air to allow heat to disperse. When it is covered by insulation, the wires can overheat, causing the protective rubber sheathing to become brittle and break down, which creates a serious fire hazard. If you find knob and tube wiring buried under insulation, you should contact a qualified electrician immediately to assess the situation and make it safe.
Find Fixture and Switch Wiring:
If you're having trouble locating wiring, find the electrical box for any light fixture on the attic floor or on the ceiling below. Check the wiring going into the box. Do you see modern, plastic-sheathed wire (typically yellow or white "Romex"), or do you see the individual wires characteristic of a knob and tube system? Often, the switch for the attic light itself is a location where the original wiring is still visible.
What to Look for to Determine if Knob and Tube Was Once Present in Your Home
Knowing knob and tube once existed in your home will tell you if you need to dig deeper into its existence behind walls. Often times the knobs and tubes will be left in the basement and or attic making this task easy. The joists above you in the basement will have two or more holes in them in the middle of the joists spanning multiple joists. These holes will be the same distance from the closest exterior wall; the tubes would be inserted in these holes allowing the wire to pass through the joists.
Has it Been Completely Rewired or Just Where Visible?
Insurance companies require that knob and tube wiring be replaced where visible and subject to physical disturbance, meaning it is permissible to keep it in walls and ceilings. New wiring will run from the panel to junction boxes mounted on the joists above you tight to the floor of the level above you. It is in these junctions that the new wiring is connected to the old knob and tube wiring creating the illusion of a home wired with modern materials and methods. The use of GFCI breakers or outlets will allow for 3 prong receptacles to be installed further, concealing the presence of a dangerous wiring infrastructure.
Don’t Rush to Conclusions, Thorough Is Imperative
Even if outlets have been rewired, that doesn’t mean the home is fully free of knob-and-tube
(K&T) wiring. In many cases, only receptacles and lighting components were updated, while K&T still remains in switches, fixtures, or other hidden areas. Identifying and addressing these remnants is crucial.
Areas often overlooked include:
Attic lighting circuits
Furnace or boiler shut-off switches.
Basement lighting and outlets
Stairwell lighting circuits
Remote or out-of-sight spaces such as crawl spaces and unfinished areas
These remnants can remain energized long after a “full rewiring” project, and issues can persist even when a professional declares the wiring complete. A quick, targeted inspection is worthwhile to ensure nothing is missed and to inform you of a comprehensive upgrade plan.
What Height Are Your Outlets At? Are They Horizontal or Vertical in Orientation?
Look at the Outlets in Any Rooms Except Your Kitchen or Bathrooms. If your outlets are at 12" above the floor or higher and vertical in orientation there is a good chance that your home, or the outlets around this height have been re-wired since your house was originally wired with knob and tube. When receptacles were installed with knob and tube wiring, in residential electrical settings, they were almost always installed on the baseboard horizontally. When rewiring current methods from knob and tube it is typically cost prohibitive to reuse the box in the baseboard resulting in new locations at 18" above finished floor. I don't know if I can remember a single incident where I saw knob and tube wiring energizing an outlet at 18" off the floor for what it's worth.
Do You Have 3-Prong or 2-Prong Outlets?
2 prong outlets, especially located on the baseboard mounted horizontally, are a telltale sign that knob and tube are present and active. The presence of 3 prong outlets doesn't necessarily mean that knob and tube are not present as a 3-prong receptacle can be installed without a ground being present. 3 prong outlets located higher than the baseboard is a strong indicator that they are not fed via knob and tube, the presence of a ground should be verified and can be done via a multi meter or plug in tester which can be purchased for around $5
Other Indicators
A general lack of receptacles throughout the home is a pretty good indication of knob and tube or an outdated wiring method. Modern wiring has spaced requirements that result in at least one receptacle per wall whereas older systems would often have one outlet per room. Just like requirements for outlets, modern code has specifications for switching resulting in a switch in every room controlling either a switched outlet or light fixture with the latter being something that was not seen with knob and tube. In short, the presence of 3 prong receptacles spaced adequately at 18” AFF combined with switching for overhead lighting offers a good indication that knob and tube is not present and active or at least in the devices/areas this is found.Case Study: Identification and Misidentification of Knob and Tube Wiring
Case Study: Identification and Misidentification of Knob and Tube Wiring
During the preparation of this guide, my company worked on a home where a local electrical contractor—well-regarded for quality workmanship—had reportedly removed all knob and tube wiring. My prior experience included supervising work for the previous homeowner during the original removal, and I observed that project decisions had not been primarily influenced by cost considerations. The structure itself was similar to other two-story homes in the neighborhood, featuring both attic and basement access.
On a recent site visit to document visual features, I discovered remnants of knobs and tubes still attached to the basement joists. The inspection revealed armored cable penetrating the ceiling, as well as switch boxes that contained inactive knob and tube wiring. Additionally, some BX cable—appearing to be live—was found physically connected to knob and tube that was believed to be discontinued.
Further tracing of these circuits led to several two-prong outlets installed in the baseboard on the first floor, which initial testing indicated were not energized. Investigation showed that a tripped breaker had cut power to this section of wiring, confirming the homeowner’s statement. After a comprehensive inspection, it was determined that both floors still had four to five outlets powered via knob and tube wiring, in addition to three lights through six switches, the emergency heating system shutoff, and the basement lighting feed.
Most wiring servicing these locations consisted of armored cable or BX, but knob and tube wiring was still present somewhere within the circuit, especially within the walls. While BX or armored cable is not classified as knob and tube and is generally allowed by code enforcement agencies, it has often been used to modify existing knob and tube systems. The presence of energized BX cable in inaccessible areas can suggest that knob and tube wiring may still exist, even if it cannot be visually confirmed without a thorough inspection.
This case demonstrates that even reputable companies may overlook the full extent of existing knob and tube wiring, highlighting the challenges in accurately identifying these systems. Repeated and careful inspections are essential to avoid such oversights. The purpose of this guide is to help prevent missed areas before, during, and after any knob and tube wiring project.
Knob & Tube Wiring: Recommended Next Steps
If your insurance company requires an inspection for knob and tube wiring, it is important to respond quickly. Failure to disclose or properly manage this type of wiring could result in the denial of claims, especially in the event of incidents such as fire.
Assessing Risk and Urgency
For homeowners who are motivated by safety, the urgency of addressing knob and tube wiring depends on personal risk tolerance. While some may find its presence alone sufficient reason to take immediate action, others may wait until more urgent issues arise. Regardless of individual preferences, there are certain conditions that should prompt every homeowner to seek immediate attention from a licensed professional.
Indicators Requiring Immediate Action
· Persistent electrical burning odors
· Switches, outlets, lights, or other devices that do not function or work intermittently
· Circuit breakers that have tripped more than once or twice in the past three to six months without an identifiable cause
· Dimming or flickering lights not related to the use of high-powered appliances
Although these symptoms may sometimes originate from sources other than knob and tube wiring, they always require prompt evaluation by a licensed electrician. Ignoring these warning signs can put personal safety and property at risk.
Evaluating the Condition of Knob and Tube Wiring
In situations that do not involve insurance considerations, there are practical steps to assess the condition of knob and tube wiring. Depending on what is found, it may be reasonable to postpone rewiring if the wiring is in acceptable condition. However, it is important to remember that even under optimal circumstances, knob and tube wiring remains a two-conductor system with inherent flaws. While professionals generally recommend replacement, financial constraints may justify a delay for some homeowners. Remediation costs can vary widely, so alternative approaches may be necessary.
To evaluate condition, a device can be removed and the insulation inspected. If the insulation cracks or disintegrates when the wire is bent, or if bare copper is exposed, the wiring is in poor condition. Wiring in favorable condition will remain flexible and intact even after such manipulation.
Steps for Professional Evaluation
· Identify what is supplied by knob and tube wiring. Grouping components by breaker provides insight into circuit loads and connected items.
· The evaluation may reveal unexpected findings about which outlets or fixtures are served by knob and tube wiring.
· If limited knob and tube circuits are found and the wiring is flexible and undamaged, immediate action may not be necessary.
· If the wiring is brittle or deteriorated, outlets should be de-energized, and replacement of switches or lighting should be delayed until rewiring is feasible.
Assessing Insulation Brittleness
Brittleness of insulation on conductors is a reliable indicator of safety. After disconnecting power at the breaker, removing a switch or outlet for visual inspection can clarify wiring condition. Manipulating old wiring may reveal insulation deterioration; brittle insulation can expose energized wires, increasing the risk of arcing and electric shock. Such hazards require prompt attention. If immediate remediation is not possible, ongoing monitoring is recommended, and any warning signs should prompt the affected circuit to remain off until reviewed by a qualified professional.
Temporary Measures to Postpone Rewiring
If the wiring is found to be structurally sound and distribution does not involve high-load devices, postponing upgrades until a major renovation or more favorable financial circumstances may be considered. For interim risk reduction, the following measures are recommended. If full rewiring is not immediately feasible, homeowners can implement interim measures to minimize risks, though these are not substitutes for full replacement.
Load Management: Avoid running an excessive number of high-powered appliances simultaneously to prevent overloading circuits. Be mindful of total electrical load.
Professional Oversight: Never attempt DIY electrical work on K&T wiring. Always consult a licensed electrician for any repairs, alterations, or extensions. Improper modifications are a leading cause of hazards.
Address Deterioration: Where K&T wiring is brittle, cracked, or shows signs of deterioration or mechanical abuse, it should be replaced immediately.
Avoid Insulation: Do not place building insulation in contact with K&T wiring. If insulation is present, the wiring in that area must be replaced.
Proper Receptacle Replacement: If replacing two-prong outlets with three-prong, they must be GFCI-protected, as a true ground is absent. Removing ground pins from modern appliances to fit two-pin receptacles is strictly prohibited.
Communication with Insurers: Proactively communicate with your insurance company about the K&T wiring and any steps being taken to address safety issues.
Provide documentation of inspections and upgrades.
The presence of K&T often indicates an older home construction (e.g., plaster walls, specific framing techniques) that makes any renovation (e.g., adding insulation, changing outlets) more complex, invasive, and potentially hazardous if not handled by professionals aware of these interconnected legacy systems. This underscores the need for a holistic, expert-led approach to home renovation in older properties, recognizing that seemingly simple updates can trigger complex safety issues due to the interaction of outdated systems.
Selecting a Residential Electrician
Large Companies
When considering a large residential electrical company, there are several advantages and potential drawbacks to keep in mind. Large companies often provide reliable scheduling and adhere closely to commitments. Technicians are specifically assigned to your project, minimizing outside interruptions. These businesses are more likely to offer firm, written quotes, and their professionalism is reinforced by branded vehicles and uniformed staff. Financing options may be available, and an established presence ensures long-term support for warranties and future needs. Large companies maintain consistent availability, making it easy to reach someone by phone or email. The risk of issues such as nonperformance after deposits are made is reduced, and greater staffing capacity allows projects to meet tight deadlines.
However, large companies generally charge higher prices. There may be a disconnect between office billing and on-site technicians, which can complicate change orders or responses to unforeseen circumstances. Technician assignments may vary based on availability, so you might encounter different staff on each visit. Some technicians operate with less supervision, and if experience varies, this could affect quality. Scheduling may involve longer lead times due to demand, and communication with estimators or project managers may only be possible through the main office. Large companies tend to offer less flexibility for alternative methods or custom solutions, and may prioritize company protocols over personalized service.
Small Companies
Small electrical companies are often owner-operated, with direct involvement or frequent oversight by the owner. Scheduling is typically quicker thanks to shorter lead times, and lower overhead costs can lead to savings for clients. These businesses are usually more open to considering alternative approaches based on client needs, and there is a higher likelihood of personalized service and diligence. The owner is typically experienced, providing assurance of expertise, and clients can expect direct and frequent communication with the owner.
On the other hand, small companies face increased risk of project delays or unanticipated absences. There is potential for cost overruns in cases of unforeseen issues, and they are less likely to offer firm, binding estimates upfront. Professional appearance and branding may be inconsistent, and limited staffing can affect the ability to assign additional personnel during busy periods or tight deadlines. Small companies are more susceptible to missing deadlines due to limited resources, and rarely offer financing options. Personal challenges, such as the owner’s absence due to vacation or illness, may result in project pauses.
Making Your Final Selection
After narrowing down the type of company that best matches your preferences and requirements, the final selection process should be straightforward. Consider availability, estimated cost, reviews from other clients, and your interaction with the person who evaluated your job. These factors should help you identify a clear winner or a few options that are most appealing.
Criteria | Large Electrical Companies | Small Electrical Companies |
Scheduling & Reliability | Reliable scheduling, closely adhere to commitments, consistent availability, easier to reach by phone/email | Quicker scheduling due to shorter lead times, but increased risk of project delays or unanticipated absences |
Staffing & Supervision | Specific technicians assigned, greater staffing capacity for tight deadlines, some may operate with less supervision | Owner-operated with direct involvement, limited ability to assign extra personnel during busy periods |
Pricing | Generally higher prices | Lower overhead, potential savings for clients |
Estimates & Quotes | More likely to offer firm, written quotes | Less likely to offer binding estimates upfront; potential for cost overruns |
Professionalism & Branding | Branded vehicles, uniformed staff, consistent professional appearance | Appearance and branding may be inconsistent |
Financing & Support | May offer financing, established presence for warranties and future needs | Rarely offer financing options |
Communication | Contact typically through main office, communication with estimators/project managers may be indirect | Direct and frequent communication with owner |
Flexibility & Customization | Less flexibility for alternative methods or custom solutions, prioritize company protocols | More open to alternative approaches and personalized service |
Risk Factors | Reduced risk of nonperformance after deposits, but possible disconnect between office and technicians | Personal challenges (owner’s absence) may pause projects; more susceptible to missing deadlines |
Quality of Work | Quality may vary based on technician experience | Owner’s expertise provides assurance of diligence and quality |
What to Expect Monetarily
Types of Cost Structures
Understanding the different cost structures available for knob and tube remediation is essential for homeowners to make informed decisions and avoid surprises during their electrical upgrades. Each cost structure has unique implications for budgeting, accountability, and project outcomes.
Estimate
An estimate is essentially a contractor’s best guess at what the total cost of the project might be. It is not a number the contractor is required to honor, and the final invoice could end up being higher or lower than the original estimate. This approach can be unfavorable for homeowners, as it leaves uncertainty about the final costs of knob and tube remediation. Contractors may use estimates to gain entry into a project, sometimes offering a lower initial cost than they know will be sufficient. The intention can be to increase the final amount invoiced through change orders or claims of unforeseen circumstances encountered during the work.
Quote
A quote provides a hard number that the contractor is obligated to honor, except in cases where changes to the scope of work or unforeseen circumstances arise. However, because much of the work for knob and tube remediation involves conditions hidden within walls, quotes can still be subject to cost increases that are difficult to dispute. In such cases, quotes may not offer much more certainty than estimates, as the variables that affect cost are not always visible before the work begins.
Time and Material
Under a time and material cost structure, the contractor invoices for labor at a predetermined hourly rate and materials at a set markup. Both time and materials are tracked throughout the project, and the final invoice reflects these totals along with any additional costs such as permit fees and waste disposal. This approach provides transparency, as homeowners can see exactly where their money is going, but it can also lead to uncertainty regarding the final project cost.
Not to Exceed Cost
The not to exceed cost structure is a variation of the time and material approach. In this model, the contractor provides a financial forecast, agreeing that the total charges will not surpass a specified maximum amount. Time and materials are tracked throughout the project, and unless the homeowner requests additional or different work, the final invoice will not exceed the agreed-upon cap. This structure offers homeowners protection against runaway costs while still allowing flexibility for necessary adjustments.
Considerations When Choosing a Cost Structure
It is important to remember that, except for the electrical service, knob and tube remediation typically involves replacing the entire home’s electrical infrastructure. This is not an appropriate time to cut corners or rush the work, as hurried projects can result in additional repairs for drywall and paint contractors due to excessive handholes and patching around boxes hastily cut in. The time and material or not to exceed cost structures help prevent these issues by allowing the electrical contractor to prioritize quality over budgetary constraints. For these reasons, choosing one of these cost structures is often the best option for both homeowners and contractors, ensuring a focus on quality and minimizing surprises.
Payment Schedules and Managing Cost Overruns
Establishing Payment Schedules
Defining a payment schedule is often more important than the cost structure itself, and it is critical not to deviate from it under any circumstances. The agreed-upon cost structure will directly influence both the schedule and the corresponding payment amounts. Care should be taken to avoid situations where the amount owed at any given point is less than the value of the work remaining to be completed. Most contractors request a significant portion of their estimate upfront, which is a common practice and should not cause concern as long as the final payment due upon completion is of similar magnitude. This approach is appropriate if the initial estimate is honored regardless of unforeseen events.
If you anticipate that change orders and cost overruns are likely with this type of project, or if your contract includes provisions for additional costs, the best payment schedule is one that is weekly, paired with daily invoicing or cost tracking. This method eliminates the uncertainty that often arises towards the end of projects with highly variable costs. Daily reporting combined with weekly invoicing ensures that both parties are consistently aware of the project's financial status, allowing for timely discussions before additional work is performed and costs are incurred.
Managing Change Orders and Cost Overruns
Nearly every contract contains clauses that protect the contractor from "unforeseen circumstances," which can lead to change orders. In knob and tube remediation, these clauses are particularly relevant since much of the wiring is concealed behind sheetrock or plaster. Such conditions create a safety net for contractors if the job requires more time and materials than initially anticipated. Realistically, it is difficult to dispute these claims, as concealed wiring often presents unexpected challenges.
Rewiring a home is labor-intensive, and regardless of a contractor's experience, the time required is often underestimated. Most contractors work under a "not to exceed" or time and material cost structure, which helps to minimize the impact of unforeseen costs. In practice, projects of this nature tend to shift to a time and material cost structure, even if a different approach was initially agreed upon. Homeowners should be cautious of quotes that are significantly lower than others, as some companies may deliberately underbid, knowing they can later justify change orders to reach a more appropriate final cost.
The central issue is that without visibility behind walls, homeowners are vulnerable to unforeseen circumstances. While experienced contractors should account for these variables in their estimates or quotes, many use them as a fallback. Ultimately, these types of projects often become time and material jobs, regardless of the initial cost structure, which emphasizes the importance of selecting a trustworthy contractor above all else.
Protecting Yourself from Bait-and-Switch Tactics and Cost Overruns
Conduct a Comprehensive Inspection
Begin by paying for a thorough inspection to determine which circuits are fed by knob and tube wiring and which are supplied via BX cabling. This step provides clarity on the condition and configuration of your home's electrical system and helps establish an accurate scope for the work to be completed.
Define the Scope of Work Clearly
Outline the scope of work in detail, specifying exactly what will and will not be rewired. This eliminates ambiguity and helps avoid “unforeseen circumstances” that could lead to additional change orders during the project.
Understand BX Cabling in Relation to Knob and Tube
Recognize that BX, or metal clad cabling, succeeded knob and tube wiring and is often connected to existing knob and tube systems. BX can conduct grounding when refed with three-conductor cabling and generally presents fewer risks than knob and tube wiring.
Establish Specific Payment Terms
Set clear and specific payment terms before any work begins. Ensure that payment schedules are strictly followed and, ideally, are based on project progress. Adhering to these terms helps maintain transparency and prevents deviations that could disrupt the project.
Avoid Unprofitable Job Scenarios
It is critical to prevent situations where the project becomes unprofitable for the contractor compared to other jobs. Problems typically arise when contractors have received a substantial portion of the payment, underestimated the workload, and face the possibility that remaining funds may not cover expenses, let alone generate profit. While this scenario is not necessarily the result of malicious intent, variable projects often exceed budgets, and insufficient communication and planning can leave all parties dissatisfied and in difficult positions.
Consider Time and Material Invoicing
Given the complexities and variables associated with knob and tube wiring—especially without removing walls and ceilings—a time and material invoicing structure is often the most suitable approach for everyone involved. This method allows for flexible adjustment of costs as the project evolves and better accommodates unexpected issues.
Implement Daily Updates
If both parties agree to a time and material cost structure, daily updates of accrued costs and work performed are recommended. This practice enables prompt resolution of any questions or concerns, addressing potential friction immediately and eliminating misunderstandings or resentments.
Maintain Open Communication
Open lines of communication before and throughout the project, along with a well-defined scope of work and payment schedule, are essential to ensuring a successful outcome. These steps help safeguard your interests and foster a collaborative relationship between homeowner and contractor.
What to Expect During Project Execution
Engaging in a project of this scope requires substantial commitment and may lead to temporary disruptions in your daily routine. Common activities include drilling, installing electrical components, ongoing discussions with technicians, and frequent trips to and from vehicles to retrieve materials. These tasks will inevitably transform your home into an active construction environment. To minimize disruptions, it is advisable to schedule work during times when you are away—such as during vacations—which can benefit both you and your contractor. Accommodating the homeowner’s schedule and minimizing inconvenience often result in increased costs. Based on our experience, projects with minimal homeowner restrictions typically cost about half as much as those requiring a high level of attentive service and maximal convenience.
As contractors, our primary goal is to meet client needs efficiently. We frequently organize our work around specific household schedules, such as nap times, and strive to provide exceptional service tailored to individual requests. Open and transparent communication regarding the desired level of service and the associated pricing is essential for a successful project. We recommend having candid discussions about which aspects add the most value to your situation so that project expenses are focused where they are most beneficial.
Establishing Clear Expectations and Planning the Workflow
Renovations involving knob and tube wiring—typically found in homes with plaster walls and baseboard receptacle placements—often require the installation of new outlets at 18 inches above finished floor (AFF). Upgrades to switches, detectors, and lighting may require additional wall cutting and wire fishing. Creating access holes in plaster or sheetrock will generate dust, and mitigation strategies such as dust containment and floor protection play a significant role in the overall level of disruption and project cost. Contractors have varying standards for cleanliness and care, so these topics should be discussed as part of the budgeting process.
Options for Preparation and Clean-Up
· Some clients choose to remove furniture and prepare rooms themselves to avoid paying skilled labor rates for preparation and clean-up.
· Others prefer a turnkey solution, where contractors handle moving and covering furnishings and arrange for post-completion cleaning services.
It is essential to clearly define who is responsible for non-electrical tasks and specify the workflow schedule for re-wiring each room.
Recommended Practices and Equipment
· Use of dust bowls for ceiling and wall drilling to minimize the spread of particles.
· Installation of zip-system barriers at doors to contain dust within designated work areas.
· Utilization of shoe covers or dedicated indoor footwear.
· Protection of floors with drop cloths or “ram board.”
· Special attention to plaster hand holes, which are heavier and may involve multiple layers, often requiring additional floor protection to prevent damage.
Some wall and ceiling openings will require patching and repainting once the project is complete. This presents an opportunity to refresh the affected surfaces. Contractors may offer patch-and-paint services or leave the areas paint-ready, allowing homeowners to save costs by handling the finishing themselves if they prefer. Electrical contractors often leave hand holes open to facilitate easier patching. It is important to agree in advance on who is responsible for restoration work and to clarify expectations regarding the final condition in which your contractor will leave the project area.
Approaches to Addressing Knob and Tube Wiring
There are three primary plans for dealing with knob and tube wiring in a home. The decision on which course of action to pursue is typically driven by monetary or safety concerns. While the motivation for addressing knob and tube wiring may vary, it is essential to be forthright about its presence, as honesty enables professionals to develop a plan that meets your specific needs efficiently. Below are the three main courses of action, each corresponding to different motivating factors:
Monetary Considerations
· Satisfying insurance requirements
Safety Concerns
· Pragmatic or partial rewiring
· Complete rewire
Cost Assumptions and Example Scenario
For the purpose of this discussion, it is assumed that the kitchen and bathrooms have been remodeled since the 1950s. These areas are expected to have modern wiring that does not pose the immediate risks associated with knob-and-tube systems, both from monetary and safety perspectives.
The baseline example is a two-story house measuring 1,800 square feet, with accessible attic and basement spaces. It is important to note that homes of similar size without attic access will face significantly higher costs due to the additional wall and ceiling repairs required. In contrast, properties with balloon construction—defined by the absence of stops or headers between floors—will generally incur lower rewiring costs and reduced expenses for drywall and paint repairs.
Baseline Pricing and Cost Reduction Factors
Baseline pricing includes itemized estimates for various work areas. For the example of a 1,850-square-foot home, costs are linear and can be scaled to the square footage of any property. As property size increases, there is a slight reduction in costs due to factors such as decreased ancillary expenses (including site visits, estimates, and material procurement) and lower mobilization and demobilization costs. This also results in greater productivity, as work is completed over consecutive days by the project team.
· 1,850–2,450 sq. ft.: No reduction
· 2,450–3,050 sq. ft.: 5% reduction
· 3,050–3,650 sq. ft.: 10% reduction
It is important to emphasize that these cost estimates are for non-custom work. Outlet, switch, and light fixture locations are assumed to remain in their existing baseboard knob-and-tube positions. Any changes to these locations, such as repurposing baseboard outlets or additional homeowner requests, may result in supplementary costs. Labor rates for these examples range from $100 to $150 per hour, and material costs are approximated.
Satisfying Insurance Company Requirements
Insurance companies generally regard knob-and-tube (K&T) wiring as safe to insure, provided it is not visible or accessible. The main risks associated with K&T wiring arise when the wiring is disturbed—this frequently occurs when devices are replaced or, even more so, during updates to light fixtures. However, insurers typically maintain that as long as K&T wiring remains hidden within walls and cannot be physically touched, there is no need to increase premiums or deny coverage.
As a result, it is standard practice to leave K&T wiring undisturbed within the walls. In accessible areas such as basements and attics, Romex wiring is installed to replace the exposed sections of K&T. This Romex is then connected to the existing K&T wiring at the points where it enters the walls. Electricians may use different methods to conceal the connections: some will position junction boxes so they completely cover the K&T wiring, while others may leave a short length (typically 4 to 6 inches) of K&T wire visible as it enters the box. The choice of method is largely inconsequential from the insurance perspective, as the primary goal is to satisfy insurance requirements rather than to change the underlying wiring system.
This approach to abating K&T wiring, combined with the installation of GFCI outlets and the replacement of two-prong outlets, can sometimes mislead home inspectors. In many cases, this results in new homeowners being surprised by the true extent of the K&T wiring that remains in the house. When evaluating homes built in this era, prospective buyers should look for signs such as junction boxes mounted tightly to the basement ceiling, remnants of K&T wiring, and the presence of two-prong or GFCI outlets on the baseboard.
Cost of Satisfying Insurance Company
To abate and replace the knob and tube in the basement of an 1,850 square foot home labor will be approximately:
Location/Item | Labor Cost | Labor Hours | Material Cost | Total Cost |
Basement | $1,500-$2,400 | 12-16 hours | $300 | $1800-$2700 |
Basement lights fed via knob and tube | $600-$900 | 4-man hours | $200 | $800-$1100 |
Switch at the top of the stairs | $300-$450 | 3 hours | $30 | $330-$480 |
Light in attic with switch | $600-$900 | 6 hours | $100 | $700-$1000 |
Total potential cost to satisfy insurance | $3,000-$4,650 |
| $630 | $3630-$5280 |
Factors Influencing Cost and Decisions for Complete Abatement & Re-wire or Re-wire Leaving Lighting Circuits
When deciding how to address aging knob and tube wiring, safety is often the priority for homeowners. This typically involves hiring professionals not only to remove and replace outdated wiring, but also to repair affected walls and ceilings—including drywall and paint work. The overall cost can vary greatly depending on the home's construction and the extent of repairs required.
In most two-story homes, access to wall spaces is facilitated by the attic for the second floor and the basement for the first floor. This arrangement allows electricians to install new wiring using methods like fishing or snaking wires directly to outlets and switches. Such approaches generally reduce the need to open large sections of walls, minimizing disruption and lowering costs associated with drywall and painting repairs. While some problematic areas may require small access holes, the attic and basement setup usually enables efficient rewiring of switches and outlets.
Historically, knob and tube wiring did not include switching and overhead lighting in bedrooms. Although a switch box may appear to contain knob and tube wiring, it is often BX (metal clad cabling). Many lighting circuits on the first and second floors were installed during remodels after the knob and tube era and feature more modern wiring methods. BX is a two-conductor system, and if installed correctly, its metal jacket can act as a ground. In many cases, properly refeeding BX wiring in the basement creates a grounded system. If the insulation inside the metal jacket is intact, retaining this wiring can offer significant cost savings and reduce risks compared to knob and tube wiring.
When knob and tube wiring exists between switches and lights, opinions on replacement vary. Some homeowners choose to retain this wiring because, with the advent of LED lighting, the electrical load is much lower and the risks of an ungrounded system are reduced for switches and lights versus outlets. Others point to the increasing use of smart home devices and the frequency of fixture and switch replacements, which may justify a full replacement. The general recommendation is that if most knob and tube wiring is being replaced, it makes sense to remove all of it. Ultimately, the decision depends on individual risk tolerance, financial considerations, and property goals. Evaluating the condition of existing electrical boxes and how they affect future lighting plans can help avoid unexpected costs, as replacing these original boxes can be particularly challenging.
Exterior lighting circuits and multi-way switches often require more labor and result in higher costs during rewiring. Replacement typically involves making access holes at each switch location and possibly additional openings to route wiring from ceiling spaces to fixtures. The process can be further complicated if original junction boxes must be replaced or if large crown molding hinders wire routing.
In typical home wiring configurations, power travels first to the light fixture before branching out to outlets and switches. Removing knob and tube wiring in the basement disconnects power for both the light and switch, necessitating the installation of a new feed to the switch and energizing only the wire running from the switch to the fixture. New technologies such as smart switches and remote companion switches can simplify wiring requirements, offering more cost-effective solutions compared to traditional methods.
Rewiring projects also present an opportunity for homeowners to upgrade the number of outlets in each room, moving from one or two to the quantity required by current electrical codes. All cost estimates provided are intended as general guidance; actual costs may vary depending on factors such as local demand, ease of access, the number of outlets and switches, and the complexity of exterior lighting installations. Illustrative per-unit pricing is presented based on a typical two-story, 1,850-square-foot home with basement and attic access.
Complete Home Rewiring Cost
Complete home re-wire including switching with 4 recessed lights per room and kitchen & bathrooms completely re-wired:
$65,500 or more depending on customization.
Scope of Work | Estimated Cost | Notes |
Complete home re-wire including switching with 4 recessed lights per room and kitchen & bathrooms completely re-wired | $50,000-$65,500 or more | Cost varies depending on customization |
Basic re-wire of knob and tube only. All switching and lighting. Not including kitchen and bathrooms. No additional receptacles. Handholes made at will | $17,500-$25,500 | $500 per additional receptacle or electrical location (approx. $10,000 for entire home). $350-$500 per recessed light added (1 per room deducted where fixture exists) |
Basic re-wire of knob and tube, no additional receptacles, wiring from switch to light left in place, no bathroom or kitchen | $10,000-$15,000 | $500 per additional receptacle or electrical location (approx. $10,000 for entire home) |
Basic re-wire of knob and tube only. Not including kitchen and bathrooms but all switching and lighting. No additional receptacles. Handholes made at will:
Service | Cost | Notes |
Re-wire (knob and tube, basic) | $15,000 | No additional receptacles, wiring from switch to light left in place, no bathroom or kitchen |
Re-wire (entire home) | $25,500 |
|
Additional receptacle/electrical location | $500 each | Approximately $10,000 for entire home |
Recessed light added | $350-$500 each | 1 per room deducted |
The Pragmatic Approach
While fully removing knob-and-tube wiring is considered the most thorough solution, the expense involved makes this option difficult for many homeowners, especially since it does not provide obvious, visible improvements. In cases where a complete rewire is financially out of reach, a more practical alternative can be adopted. This pragmatic approach offers a compromise that is clearly preferable to taking no action at all.
Most homes use only half or less of their available electrical receptacles. Furniture placement often blocks many outlets in bedrooms and living rooms, making them inaccessible or used only for minor items like table lamps or phone chargers. If an inspection confirms that the existing knob-and-tube wiring is intact and safe, it is possible to create a balanced strategy that addresses both safety and insurance requirements without necessitating a full rewire.
This method involves selectively upgrading outlets in locations where higher power is needed, mainly to support modern appliances, while retaining low-power two-prong outlets and existing lighting fixtures elsewhere. By focusing upgrades only where necessary, this approach reduces risk, satisfies insurance demands, and improves convenience throughout the home, all while keeping costs significantly lower than a full system replacement.
Additionally, limiting the use of high-draw appliances helps address concerns about knob-and-tube wiring’s ability to handle heavy electrical loads. Restricting ungrounded connections to compatible devices further mitigates associated risks. The overall cost of this approach will depend on the specific needs and energy usage patterns of each household. For example, homes with heat pumps may not require the addition of extra receptacles for window air conditioning units.
Cost of Pragmatic Approach
Location/Item | Labor Cost | Labor Hours | Material Cost | Total Cost |
Rewire where visible in basement | $1,500-$2,400 | 12-16 hours | $200-$300 | $2,700 |
Basement lights fed via knob and tube | $600-$800 | 4-man hours | $200 | $1,200
|
Switch at the top of the stairs | $330-$480 | 3 hours | $30 | $1,280 |
Light in attic with switch | $700-$1,000 | 6 hours | $100 | $1,100 |
Per outlet added at 18” AFF | $350-$450
| 3 hours | $50 | $500 |
Per recessed light added (deduct one per room as already accounted for) | $350-$500 per | 3 hours | $50 | $550 |
Conclusion:
The degree of presence, condition, means of remediation and associated costs combined with the homeowner’s risk tolerance, financial situation and short/long term goals make every situation completely unique along with its associated cost. Ultimately, when considering electrical upgrades or repairs, it is important to gather detailed quotes, understand the full scope of work, and weigh both immediate needs and long-term plans. Consulting with a licensed electrician can provide insight into the best options for your home, ensuring safety, code compliance, and value. By carefully assessing your priorities and budget, you can confidently move forward with decisions that protect your investment and provide peace of mind for years to come.
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