San Francisco’s iconic housing stock — Victorian, Edwardian, and pre-war homes — carries a certain charm that continues to attract buyers from all over the world. But alongside the bay windows, ornate staircases, and original woodwork, there often hides a serious problem: knob-and-tube (K&T) wiring.
While some owners view this early electrical system as a relic of craftsmanship, most insurers see it as a red flag. Over the last several years, California insurers have placed tighter restrictions on properties with antiquated wiring, and in San Francisco the stakes are highest because of the city’s valuable and historic homes.
This article explores, in depth, how K&T wiring affects home insurance in San Francisco: why insurers consider it risky, what options homeowners have, and how replacement or mitigation can improve insurability.
What Is Knob-and-Tube Wiring?
Origins and Usage
Knob-and-tube wiring was standard practice in American homes built roughly between the 1880s and 1940s. Electricians used porcelain knobs to support the wires and tubes to protect them where they passed through wood framing. Simple in concept and adequate for early electrical loads, it was embraced widely during the early 20th century.
Key Characteristics
- Single-insulated copper conductors: Hot and neutral wires ran separately, unlike today’s bundled cables.
- Air cooling: The open design allowed heat to dissipate naturally.
- No ground wire: Safety grounding did not exist, leaving circuits vulnerable to shock hazards.
- Cloth insulation: Prone to deterioration with heat, moisture, and age.
For its era, knob-and-tube was reliable and even innovative. But electrical demand in 1900 was a fraction of today’s. A system designed for a few lights and a radio struggles under the weight of modern appliances.
Why Insurers Are Wary of Knob-and-Tube Wiring
1. Fire Risk Perceptions
Even though data shows that properly maintained K&T wiring is not inherently dangerous, insurers operate on risk perception. The key concerns include:
- Degraded insulation that can expose conductors.
- Amateur modifications over decades (splices, over-fusing, improper insulation).
- Increased likelihood of overloading in modern homes with high electrical demand.
2. Lack of Grounding
Without a grounding path, appliances and devices are more vulnerable to surges, short circuits, and damage, raising the potential for claims.
3. Insurability Trends
Major insurers in California — State Farm, Allstate, Farmers, and others — often refuse new policies for homes with K&T or require proof of full replacement. Even if coverage is granted, premiums are higher, and coverage exclusions may apply.
4. The Problem of Documentation
Because wiring hides behind walls, insurers cannot fully verify its condition. Unknowns translate into risk, and risk translates into denial or higher premiums.
Historical Perspective: Why Knob-and-Tube Still Exists in San Francisco
San Francisco preserved much of its Victorian and Edwardian architecture, unlike many U.S. cities that rebuilt in the mid-20th century. These ornate homes survived fires, earthquakes, and redevelopment, which means their original systems — including K&T wiring — often remain.
In many cases, mid-century homeowners extended or patched wiring rather than replacing it. When appliances like refrigerators or televisions became standard, electricians tied them into old circuits. Gradually, such alterations produced a patchwork of aging circuits blended with newer ones.
The result: knob-and-tube wiring is not a rare curiosity. Today, thousands of San Francisco homes still contain K&T, typically mixed with modern wiring, making inspections and insurance evaluations more difficult.
San Francisco Context: Why the Issue Is So Pressing
The Age of the Housing Stock
- Over 60% of homes in San Francisco were built before 1940.
- Many of these homes still retain portions of their original wiring.
Real Estate Values
With median home prices above $1.3 million, insurers face potential high-value claims. Outdated wiring in a home increases what insurers see as potential risk.
Renovation Challenges
- Historic preservation rules complicate upgrades.
- High labor costs inflate rewiring expenses.
- Tight housing supply forces buyers into older homes, where K&T remains common.
Insurance Outcomes for Homes With K&T Wiring
1. Policy Denial
Many insurers will simply decline coverage once an inspection confirms the presence of K&T.
2. Coverage With Restrictions
Some companies may issue a policy but exclude fire damage related to electrical issues, rendering the coverage nearly useless.
3. Higher Premiums
Where coverage is available, premiums may be 25–50% higher compared to homes with modern wiring.
4. Forced Placement in California FAIR Plan
The California FAIR Plan is the state’s insurer of last resort. Homeowners denied coverage elsewhere may turn to FAIR, which typically offers:
- Higher costs.
- More limited coverage.
- No liability protection (must be purchased separately).
Table: Insurance Outcomes for Homes With K&T in San Francisco
| Insurance Scenario | Typical Result | Cost Impact | Coverage Quality |
| Standard Policy | Denied outright | N/A | None |
| Policy with Exclusions | Accepted with restrictions | +20–40% premium | Reduced fire coverage |
| Specialized High-Risk Carrier | Accepted | +40–60% premium | Limited |
| California FAIR Plan | Accepted | High | Basic fire-only coverage |
The Inspection Process: How Insurers Identify K&T Wiring
What Insurers Require
- Home inspection reports
- Electrical contractor statements
- Photographic documentation
Red Flags for Inspectors
- Cloth-covered wires entering porcelain knobs.
- Unfused splices or amateur repairs.
- Circuits without grounding.
- Signs of overheating or brittle insulation.
Insurers sometimes ask for a licensed electrician’s report stating the wiring is safe, but such documents are usually considered short-term measures.
Home Insurance Application Process With K&T Wiring
When applying for a policy, most insurers require:
- Disclosure of known conditions – Applicants are asked to disclose the age of their roof, plumbing, heating, and electrical systems.
- Inspection report – Insurers often send an inspector or require documentation from a licensed electrician.
- Photographs – Close-up shots of wiring near the panel or basement may be required.
- Follow-up requests – Discovery of knob-and-tube wiring may lead the insurer to require a replacement plan as a prerequisite for issuing insurance.
Policies are sometimes issued “conditionally” with the requirement that the homeowner complete rewiring within 60–90 days. Ignoring these requirements may lead to the policy being canceled.
Financial Impact: Premiums, Denials, and Hidden Costs
Premium Increases
A policy that might cost $2,000 annually for a fully updated home could run $2,600–$3,000 with old wiring. Over ten years, that difference easily exceeds partial rewiring costs.
Denial of Coverage
Some homeowners face complete denial, leaving them with no option but the California FAIR Plan. FAIR lacks liability and theft coverage, so wrap-around policies are required, raising costs further.
Transactional Costs
Mortgage lenders often require proof of insurable condition. If an insurer refuses coverage, a loan may fall through, forcing sellers to lower prices or pay for rewiring themselves.
Expanded Table: Insurance Scenarios in San Francisco
| Scenario | Typical Premium | Coverage Limitations | Notes |
| Modern Wiring | $1,800–$2,200 annually | Full coverage | Standard insurers compete for business |
| K&T with Safety Report | $2,400–$2,800 annually | May exclude fire claims related to wiring | Rarely offered by major carriers |
| K&T without Updates | Often denied | N/A | Must seek high-risk or FAIR Plan |
| FAIR Plan + Wrap Policy | $3,000–$3,800 annually | Limited fire + purchased liability | Expensive and complex |
The Cost of Replacement in San Francisco: Why It’s Higher Than Average
San Francisco homeowners face uniquely high rewiring costs. National averages hover around $8,000–$15,000. In San Francisco, quotes of $20,000–$50,000 are common.
Factors include:
- Labor costs: Bay Area electricians charge some of the highest rates nationwide.
- Historic homes: Ornate plaster, crown molding, and protected facades make rewiring delicate.
- Permitting: The city’s permitting process is complex.
- Housing density: Narrow lots and multi-unit buildings complicate upgrades.
Partial Solutions: Are They Enough?
Common Strategies
- Rewiring kitchens and bathrooms to reduce load on old circuits.
- Installing GFCIs for shock protection.
- Using AFCI breakers to detect arcing faults.
- Adding dedicated circuits for modern appliances like EV chargers.
Insurer Response
While these steps improve safety, insurers often remain unconvinced. They see K&T as an “all-or-nothing” issue. Partial upgrades may buy short-term coverage but rarely satisfy carriers long-term.
The California FAIR Plan in Depth
What It Is
The California FAIR Plan, established in 1968, ensures basic fire coverage for homeowners unable to obtain insurance elsewhere. It is funded by all insurers operating in the state.
What It Covers
- Fire
- Smoke
- Lightning
- Internal explosion
What It Doesn’t Cover
- Liability
- Theft
- Water damage
- Earthquake
Homeowners must purchase additional “Difference in Conditions” policies to fill these gaps. Combined costs are typically higher than standard coverage.
Real Estate and Resale Implications
Buyer Psychology
Prospective buyers already stretched by San Francisco’s high prices often balk at homes with K&T wiring. Even if it functions, the perception of danger depresses offers.
Appraisal Challenges
Appraisers may downgrade values when outdated wiring remains, especially if comparable homes nearby have been updated.
Case Examples
- No Sale: A Noe Valley home failed to close twice because lenders wouldn’t finance buyers without rewiring.
- Price Reduction: A Bernal Heights bungalow sold for $120,000 below asking because buyers anticipated rewiring costs.
The Role of Licensed Electricians
Why Insurers Require Licensed Work
Insurers trust licensed professionals to follow code and obtain permits. Unlicensed work often fails inspection and voids coverage.
Certification Letters
A licensed electrician can sometimes provide a safety letter confirming K&T is in usable condition. While not a substitute for rewiring, it may satisfy certain smaller insurers temporarily.
Choosing the Right Contractor
- Experience with historic homes reduces cosmetic damage.
- Knowledge of permits accelerates compliance.
- Insurance cooperation ensures reports are phrased acceptably.
Long-Term Financial Logic
Even if rewiring feels expensive, the long-term math supports it:
- Premium savings: $600 annually equals $6,000 over a decade.
- Resale advantage: Updated wiring boosts buyer confidence.
- Safety: Preventing a fire protects both family and property.
Viewed over 20–30 years, rewiring typically pays for itself several times over.
Local Case Study: A Victorian in the Mission District
A 1905 Victorian in San Francisco’s Mission District was listed at $1.8 million. The inspection revealed active K&T wiring in half the house. Coverage was denied by the insurer, and the lender immediately suspended financing. The seller ultimately offered a $40,000 credit toward rewiring to close the deal.
This case highlights the real financial impact of K&T wiring on both insurance and property transactions.
Frequently Asked Questions
Can I get insurance if my home has K&T wiring?
Possibly, but coverage will be expensive, limited, or both. Many insurers refuse outright.
Does replacing K&T wiring increase home value?
Yes. Modernized wiring brings peace of mind to buyers and discounts from insurers. In San Francisco’s competitive market, this can significantly improve saleability.
Are there legal requirements to replace K&T in San Francisco?
No blanket law mandates replacement. However, major renovations usually trigger code requirements for upgrades.
Can I leave K&T if it looks fine?
Visual appearance can be misleading. Even if wiring looks intact, insulation may be brittle inside walls. Insurers rarely accept it without replacement.
Conclusion: The Cost of Waiting
For homeowners in San Francisco, knob-and-tube wiring is far more than a relic of early electrical work — it represents a serious financial and safety concern. Outdated systems influence whether insurers will even issue a policy, drive up premiums when coverage is available, and can lower a property’s overall market appeal.
Although a complete rewire requires a significant investment, it is often the only path back to standard homeowners insurance, stable premiums, and a stronger resale position. Just as crucial, updated wiring lowers fire hazards and protects households in a city where homes carry both historic value and high price tags. Postponing rewiring simply makes the situation worse over time. Each year that knob-and-tube wiring remains in service raises the potential for coverage complications, higher costs, and safety hazards. For most San Francisco property owners, replacing outdated wiring is less a matter of preference and more a practical step toward long-term security and financial protection.