Knob and Tube Wiring: How Many Homes Date From the Era, and What Insurers Do

The market in brief

• No federal survey asks which wiring method a home has, so the number of US homes that still contain knob and tube wiring is unknown; this report measures the era and the symptoms instead.
• The ACS 2025 1-year estimates, released October 29, 2026, count 16.7 million housing units built 1939 or earlier, 11.3% of 148.2 million US homes.
• In the American Housing Survey 2023, 14.9% of occupied homes built before 1940 reported at least one of three electrical problems, against 10.2% of homes built 2000 or later, a ratio of 1.46 (standard error 0.08).
• The widest gaps are in the items least likely to reflect household habits: exposed wiring (4.0% vs 2.2%, ratio 1.82) and a room without a working wall outlet (2.5% vs 1.3%, ratio 1.92).
• Homes built in the 1930s report the highest rate of any decade, 18.4%, more than twice the 8.7% for homes built in the 2000s.
• Six of nine homeowners underwriting guidelines filed with the Maine Bureau of Insurance name knob and tube wiring: four bar any of it and two bar active knob and tube only.
• California and Washington allow insulation around existing knob and tube only after a licensed electrician certifies it; California's code bars it from hollow spaces filled with loose, rolled or foamed-in-place insulation.
• Owner-occupied homes built before 1940 were twice as likely as homes built 2000 or later to have had an electrical wiring, panel or lighting job in the prior 2 years (9.9% vs 4.9%), at a median reported cost of $1,500.

Knob and tube wiring was standard from about 1880 to the 1940s, and no survey counts what remains

Knob and tube wiring ran single insulated copper conductors on porcelain knobs and through porcelain tubes. Local agencies date its common use from about 1880 into the 1940s. The federal housing surveys ask when a home was built, not how it is wired, so the era can be measured and the wiring cannot.

Knob and tube wiring: An early wiring method in which single insulated copper conductors are run through wall and ceiling cavities, pass through joists and studs inside porcelain tubes, and are supported along their length on nailed-down porcelain knobs (City of Menlo Park). The system has no ground wire (Center for Energy and Environment, 2025).

Tacoma Power tells customers that knob and tube was the standard wiring method in homes built between 1880 and 1950. The City of Menlo Park says it was used until the 1940s, Ontario's Electrical Safety Authority dates it to the early 1900s to 1940s, and the Minnesota Center for Energy and Environment says it was phased out in the 1940s.

The first National Electrical Code, the 1897 edition, already regulated it: according to a Fire Engineering summary, supports could be no more than 4.5 feet apart and wires carrying up to 300 volts had to be at least 2.5 inches apart. The same article notes that the method was labor-intensive and gave way to conduit and to metal-sheathed and nonmetallic-sheathed cable.

The era indicator is large. The ACS 2025 1-year table B25034 counts 16,741,814 housing units built 1939 or earlier, 11.3% of the US stock, and another 6,154,761 built in the 1940s, which brings the pre-1950 share to 15.4%. Many of those homes have been partly or fully rewired, so these counts are an upper bound on exposure, not a count of the wiring.

Homes built before 1940 report exposed wiring 1.8 times as often as homes built since 2000

The American Housing Survey asks every occupied home three electrical questions. In 2023, homes built before 1940 answered yes more often on all three, and the gap is widest on exposed wiring and rooms without a working outlet.

The AHS 2023 national public use file records whether a fuse blew or a breaker tripped in the 3 months before the interview, whether finished living areas have exposed wiring, and whether any room lacks a working electric wall outlet. In 2023, 14.9% of occupied homes built before 1940 reported at least one of the three, compared with 11.6% of homes built 1940 to 1969, 10.7% of homes built 1970 to 1999 and 10.2% of homes built 2000 or later.

Item by item, pre-1940 homes reported exposed wiring at 4.0% vs 2.2% for homes built 2000 or later (ratio 1.82, SE 0.21), a room without a working outlet at 2.5% vs 1.3% (ratio 1.92, SE 0.3), three or more blown fuses or tripped breakers at 2.7% vs 1.5% (ratio 1.81, SE 0.24), and any blown fuse or tripped breaker at 10.1% vs 7.4% (ratio 1.37, SE 0.09). Standard errors come from the survey's 160 replicate weights.

Applied to the 16.2 million wired, occupied pre-1940 homes, the 4.7 percentage point gap over the 2000-or-later rate equals about 764,000 homes with a warning sign beyond what newer homes report (SE about 117,000). None of the three items names the wiring method, so this is a measure of older homes' electrical condition, not of knob and tube itself.

The 1930s housing stock, the last full knob and tube decade, reports the most problems: 18.4%

Split by decade, the rate rises through the 1920s and 1930s and drops after 1940, when local agencies say knob and tube left common use. Homes built since 2010 tick back up on the fuse item.

In 2023, 13.6% of homes built in 1919 or earlier, 14.5% of 1920s homes and 18.4% of 1930s homes reported at least one of the three electrical items. The rate falls to 11.9% for the 1940s and 11.5% for the 1960s, and reaches its low of 8.7% for homes built in the 2000s, so 1930s homes report problems at 2.12 times the 2000s rate.

Homes built 2010 or later report 11.9%, mostly through the fuse item (8.8%). That fits the Census note that new occupants trip breakers while learning a home, and it is why the newest decade is not used as the baseline in the ratios above. The 1930s estimate rests on 1,153 sample cases, the smallest decade in the file, so its standard error is the widest (see table).

Five states hold 44.4% of pre-1940 homes; DC, New York and Massachusetts have the highest shares

The ACS 2025 count of homes built 1939 or earlier is the closest public proxy for where knob and tube could still be in walls. It concentrates in the Northeast and Midwest and is near zero in the Sun Belt.

By count, New York has 2.6 million homes built 1939 or earlier, Pennsylvania 1.4 million, California 1.3 million, Illinois 1.1 million and Ohio 1.0 million; together they hold 7.4 million, or 44.4% of the national total. By share, the District of Columbia (31.9%), New York (30.1%), Massachusetts (30.0%), Rhode Island (27.7%) and Pennsylvania (23.5%) lead, and 9 jurisdictions are at 20% or more.

At the other end, homes built before 1940 make up 1.2% of housing in Nevada, 1.3% in Arizona, 1.6% in Alaska and 1.8% in Florida. For median home ages and the 30 to 49 year band, see How old is my house?; this table covers only the pre-1940 band.

As a cross-check, the AHS 2023 estimate of 16.3 million occupied pre-1940 homes equals 97.2% of the ACS 2025 count of all units built 1939 or earlier, which also includes vacant homes. The two surveys use different years and universes, so the match is a sanity check, not a reconciliation.

Six of nine insurer guidelines filed in Maine name knob and tube wiring

Insurers rarely publish underwriting rules, but Maine's insurance regulator posts the homeowners guidelines that insurers file with it. Of nine found, six name knob and tube wiring as a reason a home is ineligible or unacceptable.

State Farm's Maine guidelines, effective January 1, 2023 and produced under a Maine Bureau of Insurance data call, list "a dwelling with" knob and tube wiring under unacceptable building service equipment. Hannover (effective December 3, 2018) and both Integon National editions (April 25, 2019 and an undated OneChoice and Premier Client edition) list knob and tube wiring among ineligible risks. Two Farmers editions (October 5, 2021 and December 9, 2022) bar only active knob and tube wiring.

Three files do not name it: USAA (February 24, 2023) bars dwellings with inadequate or faulty wiring or insufficient amperage, an unnamed insurer form PL-12430 requires circuit breakers in whole or in part, and the Chubb file (August 1, 2022) has no wiring rule. That puts the count at 6 of 9, or 66.7%. These are 2018 to 2023 editions read through archived copies, and insurers may have revised them since.

In Florida, Citizens Property Insurance Corporation publishes a sample 4-Point Inspection Form (Insp4pt 01 18) whose electrical section asks the inspector to check cloth wiring, active knob and tube, and branch circuit aluminum wiring. The form says underwriting will rely on it to determine insurability. Citizens' full underwriting manual was not found in an openable copy, so this report does not state Citizens' eligibility rule.

Reporting shows the rules tightening over time. In 2003 a State Farm spokeswoman told The Seattle Times the company had no hard and fast rule on knob and tube in Washington and judged each home case by case. In March 2025, ABC7 San Francisco reported insurers declining and canceling Bay Area policies over it, while the San Francisco Fire Department told the station it had not seen trends in knob and tube residential fires. Ontario's Electrical Safety Authority wrote in 2022, and again in 2025, that many insurers there will not provide or renew coverage.

Insulation packed around live knob and tube is a code question in California and Washington

Knob and tube conductors were designed to run in open air, held away from wood. Codes treat burying them in insulation as a separate issue from simply leaving them in place.

California Electrical Code section 394.12 item 5, quoted on Berkeley Form 146 and the Menlo Park building page, says concealed knob and tube shall not be used in hollow spaces of walls, ceilings and attics insulated with loose, rolled or foamed-in-place material that envelops the conductors. An exception allows insulation if a licensed electrical contractor certifies the wiring is in good condition, the certificate is filed, bilingual caution notices are posted at attic accesses, and the insulation is noncombustible with no conductive material.

Washington's rule WAC 296-46B-394, amended effective April 1, 2024, reads NEC Article 394 as allowing loose or rolled insulation around existing knob and tube on three conditions: a licensed contractor certifies the wiring to the state, the insulation is Class I with a flame spread of 25 or less and is not foam, and every circuit has overcurrent protection matched to NEC Table 310.16's 60 degree column by breakers or Type S fuses.

The concern is heat. Fire Engineering describes knobs that held each wire at least half an inch off the framing, and an inspection firm's explainer says packed insulation stops the wire covering from shedding heat. Tacoma Power requires an electrician's inspection before an insulation project in its rebate and loan program, citing improper splices, damaged knobs and oversized fuses or breakers; its form lists 15 amp protection for 14 gauge and 20 amp for 12 gauge conductors. For attic insulation that may itself be a hazard, see vermiculite insulation.

Electrical jobs in pre-1940 owner homes: twice as common, at a median $1,500

No public dataset prices knob and tube replacement. The AHS does record what owners spent on electrical wiring, panel and built-in lighting jobs, which is the closest sourced cost figure, and it shows older homes doing this work more often.

In the 2 years before the 2023 survey, 9.9% of owner-occupied homes built before 1940 had an electrical wiring, fuse box, breaker panel or built-in lighting job, against 4.9% of homes built 2000 or later, a ratio of 2.01. The weighted median reported cost of those jobs was $1,500 in pre-1940 homes (289 sample jobs, mean $3,570) and $700 in homes built 2000 or later (315 sample jobs). Across all owner homes the median was $1,000.

These figures mix small jobs with whole-house rewiring, and the public file rounds and topcodes costs, so they are not a rewiring price. Two of the pages that rank for this topic quote replacement ranges of $3,500 to $8,000 (Waypoint) and $5,000 to $10,000 for a 1,500 to 3,000 square foot home (Mr. Electric), with no source or method; they are reported here as claims and not used as data. For how electrical work fits a remodel budget, see bathroom remodel cost.

Is knob and tube wiring dangerous? Federal fire data cannot single it out

National fire statistics count electrical malfunction fires but do not record the wiring method, so there is no published US fire rate for knob and tube. Regulators point to age, alterations and insulation as the risk factors.

The U.S. Fire Administration estimates 23,700 residential building electrical malfunction fires in 2023, with 305 deaths, 800 injuries and $1.5 billion in losses; deaths fell 19% from 2014 to 2023. Those totals cover all wiring types and appliances.

Ontario's Electrical Safety Authority lets existing knob and tube stay in service if it is protected by a 15 amp fuse or breaker, has no added outlets and looks sound, and lists the unsafe changes it sees: oversized 20 or 30 amp fuses, extension cords used as permanent wiring, new receptacles tapped onto old circuits and removed ground pins. The Center for Energy and Environment adds that the rubber insulation turns brittle with heat and age. The AHS signal above is consistent with that picture of aging, altered systems; it does not prove that knob and tube itself fails more often.

Older two-prong circuits also intersect the GFCI rules covered in GFCI requirements by NEC edition, which this report does not repeat.

What a kitchen or bath remodel in a pre-1940 house runs into

A remodel is when old wiring gets exposed, and building departments treat new work and old work differently. Local permit rules, not national data, decide what must change.

The City of Menlo Park states that new knob and tube installation is no longer allowed under the California Electrical Code except by special permission, and recommends that knob and tube found during construction be removed entirely or in part to the maximum extent practical. Berkeley requires permits and inspections, and Washington requires inspection, for repairs, alterations or extensions of an existing system (Form 146, WAC 296-46B-394).

Opening plaster in a pre-1940 kitchen or bath can also disturb lead paint and asbestos; see when lead paint was banned and when asbestos was banned. Rewiring adds inspection steps to a schedule (kitchen remodel timeline), and contractor vetting is covered in how to choose a remodeling contractor.

Local benchmarks we calculated

Download the calculations (CSV)

What the numbers show

1. 16,741,814 US housing units were built 1939 or earlier, 11.3% of the 2025 housing stock (ACS 2025 1-year, B25034).^[7]
2. Adding the 6,154,761 homes built in the 1940s, 15.4% of US homes date from before 1950 (ACS 2025).^[7]
3. 14.9% of occupied US homes built before 1940 reported a blown fuse or tripped breaker in the last 3 months, exposed wiring, or a room without a working outlet in 2023, vs 10.2% of homes built 2000 or later (AHS 2023).^[1]
4. The pre-1940 to 2000-or-later ratio for those three items combined is 1.46, with a replicate-weight standard error of 0.08 (KBR calculation, AHS 2023).^[1][5]
5. 4.0% of pre-1940 homes reported exposed wiring in finished living areas in 2023, vs 2.2% of homes built 2000 or later, a ratio of 1.82 (AHS 2023).^[1]
6. 2.5% of pre-1940 homes had a room without a working electric wall outlet in 2023, vs 1.3% of homes built 2000 or later (AHS 2023).^[1]
7. Homes built in the 1930s had the highest rate of any decade in 2023: 18.4% reported at least one of the three electrical items (AHS 2023).^[1]
8. Across all 133,231 thousand occupied US homes, 10,429 thousand had a fuse blown or breaker tripped in the 3 months before the 2023 interview (AHS 2023, matching the Census published PUF estimate).^[1][2]
9. New York (2,634,166), Pennsylvania (1,381,651), California (1,284,468), Illinois (1,117,920) and Ohio (1,011,876) hold 44.4% of all US homes built 1939 or earlier (ACS 2025).^[7]
10. The District of Columbia (31.9%), New York (30.1%) and Massachusetts (30.0%) have the highest shares of homes built 1939 or earlier; Nevada (1.2%) has the lowest (ACS 2025).^[7]
11. State Farm's Maine homeowners guidelines effective January 1, 2023 list a dwelling with knob and tube wiring as unacceptable.^[17]
12. Farmers' Maine guidelines dated October 5, 2021 and December 9, 2022 bar homes with active knob and tube wiring.^[18][19]
13. Citizens Property Insurance Corporation's sample 4-Point Inspection Form (Insp4pt 01 18) asks Florida inspectors to mark active knob and tube wiring, and Citizens says underwriting uses the form to determine insurability.^[16]
14. US fire departments responded to an estimated 23,700 residential building electrical malfunction fires in 2023, with 305 deaths; the federal data do not identify wiring type (USFA).^[10]
15. 9.9% of owner-occupied pre-1940 homes had an electrical wiring, panel or built-in lighting job in the 2 years before the 2023 survey, vs 4.9% of homes built 2000 or later (AHS 2023).^[1]

Frequently asked questions

Related guides, services and research

• How to choose a contractor
• How long a kitchen remodel takes
• Home Improvement Loan Rates and Approval Data (HMDA 2025)
• Home Improvement Statistics: Kitchen and Bath Remodels (AHS 2023)
• How Long Do Appliances Last? The Federal Lifetime Index for 20 Home Appliances
• How Long Do Copper Pipes Last? Pipe Lifespans by Material and Water
• All kitchen and bath research

Reproduce this analysis

Every figure comes from the files below. The scripts that pulled and computed them are kept with the report and can be re-run.

Data quality and exclusions

• Removed 7,142 household rows that are not occupied interviews (vacant or usual residence elsewhere), leaving 48,527 occupied rows.
• Fuse items exclude occupied homes with no electrical wiring (NOWIRE = 3, 121 thousand weighted), as in the Census table; the combined item uses the same base.
• FUSEBLOW = N (not applicable) and PLUGS = N are counted as no; no imputation was added.
• Project file: kept 2,097 job type 23 rows with JOBDIY 1 or 2; 1,995 owner-occupied jobs with a reported cost above zero went into the medians.
• ACS: kept the US row and 51 state and DC rows of the B25034 file; Puerto Rico and substate rows were dropped.
• Maine guidelines: maine.gov refused automated requests (access denied), so 9 files were read from Internet Archive captures; GuideOne's knob and tube PDF was no longer online and was dropped.

Methodology

Source selection: the American Housing Survey 2023 national PUF v1.1 (released January 22, 2025, the latest national file) for electrical deficiency items and home improvement jobs; ACS 2025 1-year table B25034 from the Census table-based summary file (released October 29, 2026) for homes by year built; the USFA fire trends page; state and city code documents; insurer guidelines posted by the Maine Bureau of Insurance; and the Citizens 4-Point form. Tier 3 journalism is used only for dated statements.

AHS estimates: occupied units (INTSTATUS = 1), weighted by WEIGHT. Items: FUSEBLOW (1 to 4 = at least one blown fuse or tripped breaker in 3 months; 3 and 4 = three or more), NOWIRE = 2 (exposed wiring), PLUGS = 2 (a room without a working wall outlet). Fuse shares use homes with wiring (NOWIRE 1 or 2) as the base, matching Census table C-05-AO. Year-built bands come from YRBUILT. Standard errors use the 160 replicate weights with variance = 4/160 x sum of squared deviations, per the Census quick guide.

Verification: the recomputed national totals match the Census published PUF estimates exactly: 133,231 thousand occupied homes, 3,721 thousand with exposed wiring, 2,247 thousand with a room lacking outlets and 10,429 thousand with a blown fuse or tripped breaker (verification_log.md).

Home improvement jobs: AHS project file, JOBTYPE 23 (electrical wiring, fuse boxes, breaker panels or built-in lighting), linked to owner-occupied households by CONTROL; medians are weighted by the household weight and use jobs with JOBCOST above zero.

Insurer registry: the nine Maine guideline PDFs were found on maine.gov, which blocked automated downloads, so each was read from an Internet Archive capture of the official file and labelled as such. Each was coded as bars any knob and tube, bars active knob and tube only, general wiring rule, or not named. Conflicting dates for when knob and tube left use (1940s vs 1950) are shown side by side.

Data last updated November 2, 2026. Next scheduled updates: the AHS 2025 national PUF and ACS 2026 1-year estimates.

This report presents published data with its limitations. It is not legal, financial or investment advice.

Sources, ranked by quality

Tier 1: primary and official sources (27)

• [1] U.S. Census Bureau and HUD. American Housing Survey 2023 National Public Use File v1.1 (CSV). 2023 survey; PUF v1.1 released January 22, 2025. Accessed 2026-11-02.
• [2] U.S. Census Bureau. AHS 2023 Table Specifications and PUF Estimates for User Verification. 2023. Accessed 2026-11-02.
• [3] U.S. Census Bureau. American Housing Survey for the United States: 2023, Definitions. 2023. Accessed 2026-11-02.
• [4] U.S. Census Bureau. AHS 2023 Value Labels Package. 2023. Accessed 2026-11-02.
• [5] U.S. Census Bureau. Quick Guide to Estimating Variance Using Replicate Weights: 2009 to Current. 2009 to current. Accessed 2026-11-02.
• [6] U.S. Census Bureau. 2023 AHS National PUF Versioning Document. v1.0 September 25, 2024; v1.1 January 22, 2025. Accessed 2026-11-02.
• [7] U.S. Census Bureau. American Community Survey 2025 1-year, Table B25034 Year Structure Built (table-based summary file). 2025 (released October 29, 2026). Accessed 2026-11-02.
• [8] U.S. Census Bureau. ACS 2025 1-year Table Shells (B25034 line labels). 2025. Accessed 2026-11-02.
• [9] U.S. Census Bureau. 2025 ACS Data Release Schedule. Updated October 29, 2026. Accessed 2026-11-02.
• [10] U.S. Fire Administration (FEMA). Residential Building Electrical Malfunction Fire Trends (2014-2023). 2014 to 2023. Accessed 2026-11-02.
• [11] Washington State Legislature (Department of Labor and Industries rule). WAC 296-46B-394 Concealed knob-and-tube wiring (certified 3/13/2024). Effective April 1, 2024. Accessed 2026-11-02.
• [12] City of Berkeley Building and Safety. Form 146: Knob-and-Tube Wiring Safety Report (last revised 03/25/26). 2025 California Electrical Code. Accessed 2026-11-02.
• [13] City of Menlo Park Building Division. Knob and Tube Safety Wiring Requirements. 2025 California codes. Accessed 2026-11-02.
• [14] City of Menlo Park Community Development. Knob and Tube Safety Requirements for Attics (form). 2025 California Electrical Code. Accessed 2026-11-02.
• [15] Tacoma Power (City of Tacoma). Knob & Tube Wiring Inspection Requirements, Form 3504 (rev. 2/2018). Form revised February 2018. Accessed 2026-11-02.
• [16] Citizens Property Insurance Corporation (Florida). 4-Point Inspection Form, Sample Form Insp4pt 01 18. Form edition 01 18. Accessed 2026-11-02.
• [17] State Farm via Maine Bureau of Insurance (Internet Archive capture 2024-05-20). State Farm Underwriting Guidelines, Homeowners, Maine (effective 1/1/2023), filed with the Maine Bureau of Insurance; Internet Archive capture of the maine.gov file. Effective January 1, 2023. Accessed 2026-11-02.
• [18] Farmers via Maine Bureau of Insurance (Internet Archive capture 2024-05-17). Farmers Property and Casualty Insurance Company, Maine Homeowner New Business Underwriting Guidelines (October 5, 2021); Internet Archive capture of the maine.gov file. October 5, 2021. Accessed 2026-11-02.
• [19] Farmers via Maine Bureau of Insurance (Internet Archive capture 2024-05-18). Farmers Casualty Insurance Company (FCAS), Maine Homeowner Underwriting Guidelines (December 9, 2022); Internet Archive capture of the maine.gov file. December 9, 2022. Accessed 2026-11-02.
• [20] Hanover Insurance Group via Maine Bureau of Insurance (Internet Archive capture 2024-07-19). Hannover, Maine Homeowners Underwriting Guidelines (effective 12/03/2018); Internet Archive capture of the maine.gov file. Effective December 3, 2018. Accessed 2026-11-02.
• [21] Integon National via Maine Bureau of Insurance (Internet Archive capture 2024-05-18). Integon National Insurance Company, Maine Homeowners OneChoice (revised April 25, 2019); Internet Archive capture of the maine.gov file. Revised April 25, 2019. Accessed 2026-11-02.
• [22] Integon National via Maine Bureau of Insurance (Internet Archive capture 2024-05-17). Integon National Insurance Company, Homeowners Guidelines OneChoice and Premier Client, Maine (undated; file created October 12, 2020); Internet Archive capture of the maine.gov file. Undated (PDF created 2020-10-12). Accessed 2026-11-02.
• [23] USAA via Maine Bureau of Insurance (Internet Archive capture 2024-05-20). USAA Group Homeowners Insurance Underwriting Guidelines, Maine (Rev. Eff. 02/24/2023); Internet Archive capture of the maine.gov file. Effective February 24, 2023. Accessed 2026-11-02.
• [24] Chubb via Maine Bureau of Insurance (Internet Archive capture 2024-07-19). Homeowners Underwriting Guidelines, State: Maine (effective 08/01/2022), Chubb writing companies; Internet Archive capture of the maine.gov file. Effective August 1, 2022. Accessed 2026-11-02.
• [25] Unnamed insurer via Maine Bureau of Insurance (Internet Archive capture 2024-05-17). Maine Homeowners New Business Eligibility and Pricing Guidelines, form PL-12430 (01-07), insurer not named on the form; Internet Archive capture of the maine.gov file. Form edition 01-07. Accessed 2026-11-02.
• [26] Electrical Safety Authority (Ontario, Canada). Flash 25-05-FL: Knob and tube wiring in residential installations (May 2025). May 2025. Accessed 2026-11-02.
• [27] Electrical Safety Authority (Ontario, Canada). Flash 22-16-FL: Knob and tube wiring in residential installations (May 2022). May 2022. Accessed 2026-11-02.

Tier 2: trade bodies, market research, company data (1)

• [28] Center for Energy and Environment (Minnesota nonprofit). Dealing with knob-and-tube wiring (February 5, 2025). 2025. Accessed 2026-11-02.

Tier 3: journalism and expert commentary (5)

• [29] ABC7 News (KGO-TV). Bay Area homeowners could get coverage denied or canceled for having outdated knob and tube electrical system (March 13, 2025). 2025. Accessed 2026-11-02.
• [30] The Seattle Times. Condition of knob and tube wiring is key to getting older home insured (January 25, 2003). 2003. Accessed 2026-11-02.
• [31] Fire Engineering. Construction Concerns: Knob and Tube Wiring (November 13, 2008). 2008. Accessed 2026-11-02.
• [32] Waypoint Property Inspection. Knob and Tube Wiring (February 24, 2021). 2021. Accessed 2026-11-02.
• [33] Mr. Electric. What is Knob and Tube Wiring?. Undated. Accessed 2026-11-02.