Quick Answer
Knob-and-tube is an early wiring method — named for the ceramic knobs and tubes that support it — common in homes built before roughly the 1950s, including many in San Anselmo and Fairfax. It has no ground, was never designed for modern loads, and its insulation can degrade with age. That doesn’t mean instant danger, but it’s a real concern for safety, insurance, and capacity. A licensed electrician assesses its condition and, where warranted, rewires the home carefully — usually in stages, without gutting it.
Key Takeaways
- Knob-and-tube wiring is an early method common in pre-1950s homes, including much of San Anselmo and Fairfax’s character housing stock.
- Its main concerns are the lack of a ground, no capacity for modern loads, aging insulation, and problems when it’s buried in insulation or altered by amateurs.
- Age alone isn’t an emergency, but knob-and-tube frequently complicates home insurance and can’t safely support today’s electrical demand.
- A rewire replaces the old wiring with modern grounded circuits, usually done in stages with care for the home’s original finishes.
- A licensed electrician assesses condition honestly — some knob-and-tube can be managed for a time, but much of it warrants replacement.
Knob-and-tube wiring is an early electrical wiring method, named for the ceramic knobs that anchor the wires and the ceramic tubes that protect them where they pass through framing, common in North American homes built before roughly the 1950s. It carried power reliably for its era, running individual conductors through the structure with air space around them for cooling. The method wasn’t crude — it was the standard of its day — but its day was a time of far lighter electrical demand, before grounded circuits, before the loads a modern household places on its wiring. That gap between then and now is the heart of the issue.
What is knob-and-tube wiring?
The defining limitations are structural to the method. Knob-and-tube has no ground wire, the safety conductor that modern wiring uses to protect against shock and faults, because grounding simply wasn’t part of the original system. It was also sized for the modest loads of its time, not today’s appliances and electronics. And its cloth-and-rubber insulation can grow brittle over the decades. None of this makes every knob-and-tube installation an immediate hazard, but it’s why authorities and insurers treat it as a serious consideration. Fire-safety guidance from the Electrical Safety Foundation International consistently flags aging and outdated wiring as a home-safety concern.
Knob-and-tube wiring is an early wiring method using ceramic knobs and tubes to run and protect conductors, common in pre-1950s homes; it lacks a ground and wasn’t designed for modern loads.
Why San Anselmo and Fairfax homes often have it
San Anselmo and Fairfax are exactly the kind of towns where this comes up. Their appeal is their older, character-rich homes — early-20th-century cottages, craftsman houses, and hillside homes that predate the postwar building boom. Many of these were originally wired with knob-and-tube, and while some has been replaced over the decades, plenty remains hidden in walls, attics, and crawlspaces. If you own or are buying one of these homes, knowing what’s behind the plaster matters. For the broader picture on the method and its remediation, our guide to knob-and-tube wiring for Marin home buyers covers it in depth.
A ground wire is the safety conductor in modern wiring that protects against shock and electrical faults — a feature knob-and-tube wiring does not include.
Is knob-and-tube wiring dangerous?
Knob-and-tube wiring isn’t automatically dangerous, but it carries real risks that grow with age, alteration, and modern demand — the lack of a ground, aging insulation, and a design never meant for today’s loads. In good, undisturbed condition, some knob-and-tube can operate for a time; the problems arise when it’s overloaded, when its insulation has degraded, when amateurs have spliced into it poorly, or when it’s been buried in thermal insulation that traps heat the original air-cooled design relied on venting. Those are the conditions that turn an old-but-stable system into a hazard, and they’re common in homes that have changed hands and been modified over decades.
The conditions that make it worse
The conditions that make knob-and-tube more hazardous are overloading it with modern appliances, covering it with blown-in or batt insulation, and amateur modifications that break its original design. The method depended on open air around the conductors to shed heat; packing insulation against it removes that cooling, which is why building codes restrict burying knob-and-tube in insulation. Poorly done splices and extensions — a light fixture added here, an outlet there, without proper technique — introduce loose connections and ungrounded hazards. These aftermarket changes, more than the original wiring, are often what pushes an old system into unsafe territory. Our guide to aluminum branch wiring covers a related concern in slightly newer homes.
Knob-and-tube didn't fail these homes — the decades of modern demand and amateur splices piled onto it did.— Towery Electric
What are the options for dealing with knob-and-tube?
The options for dealing with knob-and-tube are a full rewire, a partial or phased rewire, or — in limited cases — managing sound sections while replacing the problem ones. The right choice depends on the wiring’s condition, how much of it remains, the home’s electrical needs, and often insurance requirements. A full rewire is the most thorough and is frequently the honest answer for a home still substantially on knob-and-tube. A phased approach spreads the work over time. Managing existing wiring is only appropriate where an assessment confirms it’s sound and undisturbed. The table below compares the approaches.
Insurance is often the deciding factor that homeowners don’t anticipate. Many insurers are cautious about knob-and-tube, sometimes requiring replacement or charging more to cover a home that has it — a practical reality that turns an optional upgrade into a necessary one. This is worth confirming with your carrier early. As with any assessment, an honest electrician will tell you which sections genuinely need replacement and which don’t, rather than defaulting to the largest possible scope. Our guide on home insurance and your electrical panel covers how wiring and panel condition intersect with coverage.
| Approach | Best suited for | Consideration |
|---|---|---|
| Full rewire | Homes substantially on knob-and-tube; insurance needs | Most thorough; done carefully to protect finishes |
| Phased/partial rewire | Spreading cost; replacing worst sections first | Prioritizes hazards and high-use circuits over time |
| Manage sound sections | Limited, verified-good, undisturbed wiring | Only where an assessment confirms condition; not always accepted by insurers |
| Rewire with panel upgrade | Homes also needing more capacity | Combines rewiring with modern grounded service |
How does rewiring an older home work?
Rewiring an older home is a careful, planned process: assess the existing wiring, plan the new circuits and routing, run modern grounded wiring with minimal disruption to finishes, then connect, permit, and inspect. The concern homeowners raise most — ‘do you have to tear my walls apart?’ — is exactly what a skilled rewire is designed to avoid. Experienced electricians use existing wall cavities, attics, crawlspaces, and careful access points to route new wiring while preserving the plaster, trim, and character that make these San Anselmo and Fairfax homes worth keeping. The steps below outline how it’s done.
- Assess the existing wiring. We inspect what’s there — its condition, extent, and how it’s been modified — to plan an honest scope.
- Plan circuits and routing. We design modern grounded circuits and the least-disruptive routing through cavities, attics, and crawlspaces.
- Run the new wiring. We install new grounded wiring with care for the home’s finishes, replacing knob-and-tube section by section.
- Connect, permit, and inspect. We tie the new circuits into an appropriate panel, pull the permit, and have the work inspected before it’s energized.
The routing step is where craftsmanship shows: a thoughtful rewire finds paths through the structure that keep wall and ceiling repair to a minimum, so the home comes out modernized but not scarred. Many rewires pair naturally with a panel upgrade, since a home moving off knob-and-tube often also needs modern grounded service and more capacity. Our guide to whole-home rewiring costs and timeline in Marin covers what to expect on the scope and schedule of a full project.
Wondering if your San Anselmo or Fairfax home has knob-and-tube? Let's take a look.
Request Your EstimateWho needs to address knob-and-tube wiring?
The homeowners who most need to address knob-and-tube are those buying or selling an older San Anselmo or Fairfax home, those facing insurance requirements, and those whose wiring shows signs of trouble or can’t support their needs. For buyers, an inspection flagging knob-and-tube is a moment to understand condition and cost before closing. For owners, insurance renewals or planned electrical additions often force the question. And any home where the wiring is failing, has been buried in insulation, or has been amateur-modified is a candidate for remediation regardless of a transaction. The common thread is that the decision follows condition and circumstance, not age alone.
When it can wait — and when it can't
Addressing knob-and-tube can sometimes wait when an assessment confirms the wiring is sound, undisturbed, not overloaded, and your insurer accepts it — but it can’t wait when the insulation is failing, the system is overloaded, amateur splices are present, or coverage depends on replacement. The honest answer varies by home, which is why an assessment matters more than a blanket rule. A trustworthy electrician will tell you when sound sections have life left rather than pushing an unnecessary full gut. If your older home also needs more capacity, our guide to panel upgrades in Marin covers pairing a rewire with a modern service.
What are the common mistakes with knob-and-tube?
The most common mistake is treating knob-and-tube as either harmless or a five-alarm emergency, when the truth is condition-dependent. Assuming it’s fine because ‘it’s worked for 90 years’ ignores aging insulation and modern overloading; panicking and gutting a sound home wastes money and character. Another frequent error is amateur modification — adding circuits or outlets to knob-and-tube without proper technique — which introduces exactly the ungrounded, loose-connection hazards that make old wiring dangerous. Fire-safety authorities like the U.S. Fire Administration tie home electrical fires to outdated and improperly modified wiring.
How to handle knob-and-tube the right way
Handle knob-and-tube the right way by getting an honest assessment from a licensed C-10 electrician, confirming your insurance position early, and rewiring where warranted with care for the home’s finishes. That means resisting both complacency and panic, and being wary of any contractor who quotes a full gut without inspecting, or who offers to ‘just add a few circuits’ to the old system without proper method. A careful, permitted rewire modernizes the home’s safety and capacity while preserving what makes it special. For buyers weighing an older home, our knob-and-tube buyer’s guide covers what to know before you purchase.
Key Terms
- Knob-and-tube wiring
- An early wiring method using ceramic knobs and tubes, common in pre-1950s homes; it lacks a ground and wasn't built for modern loads.
- Ground wire
- The safety conductor in modern wiring that protects against shock and faults, absent in knob-and-tube.
- Rewire
- Replacing a home's old wiring with modern grounded circuits, often done in stages to preserve finishes.
- Insulation (wire)
- The protective covering around a conductor; on knob-and-tube it can grow brittle with age, becoming a concern.
About the Author
Founder of Healthcare Marketing Group and author of The Ultimate Guide to Digital Marketing. Previously led a digital marketing company with 8,000+ clients. Writes on local-service SEO and E-E-A-T content strategy.
Reviewed By
Alex founded Towery Electric in Novato in 2014 and has rewired character homes throughout San Anselmo, Fairfax, and the Ross Valley. Reviewed this article for technical accuracy on Sep 19, 2026, 2026.
“People fear the words ‘knob-and-tube’ more than they need to — and sometimes less than they should. My job is to tell them honestly which it is for their home, and if we rewire, to do it without tearing apart the plaster that gives these houses their soul.”
— Alex Towery, Licensed Electrical Contractor
How We Ensure Accuracy
Sources
- Electrical Safety Foundation International. “Older Home Wiring and Electrical Safety.” esfi.org
- National Fire Protection Association. “NFPA 70 — National Electrical Code.” nfpa.org
- U.S. Fire Administration. “Home Electrical Fire Safety.” usfa.fema.gov
- U.S. Consumer Product Safety Commission. “Home Electrical Safety.” cpsc.gov
- California Contractors State License Board. “License Detail — Towery Electric, Inc. (#989290).” cslb.ca.gov
Frequently Asked Questions
Is knob-and-tube wiring safe?
Knob-and-tube isn’t automatically unsafe, but it carries real risks that grow with age and modern use. It has no ground wire, wasn’t designed for today’s loads, and its insulation can grow brittle over decades. In sound, undisturbed condition some can operate for a time, but overloading, being buried in insulation, or amateur splices make it hazardous. Whether yours is a concern depends on its condition — a licensed electrician’s assessment gives you an honest answer rather than a blanket verdict.
Why do so many San Anselmo and Fairfax homes have knob-and-tube?
Because these towns are known for their older, character-rich homes — many built in the early 20th century, before the postwar building boom and before modern grounded wiring became standard. Knob-and-tube was the wiring method of that era, so homes from that period were often originally wired with it. While some has been replaced over the decades, plenty remains hidden in walls, attics, and crawlspaces of these homes, which is why it comes up so often in the Ross Valley.
Will knob-and-tube wiring affect my home insurance?
Often, yes. Many insurers are cautious about knob-and-tube, sometimes requiring its replacement as a condition of coverage or charging more to insure a home that has it. This is a common and practical reason homeowners rewire, beyond safety alone. It’s worth confirming your carrier’s position early, especially when buying an older San Anselmo or Fairfax home, so you understand any requirements before closing. A licensed electrician can document the wiring’s condition to support those conversations.
Do you have to tear up the walls to rewire an older home?
Not necessarily. A skilled rewire is specifically designed to minimize disruption, using existing wall cavities, attics, crawlspaces, and careful access points to route new wiring while preserving plaster, trim, and character. Some patching is usually needed, but a thoughtful electrician keeps it to a minimum rather than gutting the home. Preserving what makes these older San Anselmo and Fairfax homes special is part of doing the job well, not an afterthought to the electrical work.
How much does it cost to rewire a knob-and-tube home?
Cost depends on the home’s size, how much knob-and-tube remains, the routing complexity, and whether a panel upgrade is included — so an honest figure comes after an assessment. A phased rewire can spread the cost by tackling the worst sections first. A licensed electrician can scope it accurately after inspecting what’s there and how it’s been modified. Because insurance sometimes requires replacement, it’s worth understanding both the electrical need and any coverage requirement together.
Editor’s Summary
The character homes of San Anselmo and Fairfax often carry knob-and-tube wiring — an early method that lacks a ground and was never built for modern loads. It isn’t automatically dangerous, but aging insulation, overloading, buried wiring, and amateur splices turn it into a real concern for safety and insurance. A licensed C-10 electrician assesses condition honestly and, where warranted, rewires the home carefully in stages, modernizing its safety without gutting the plaster that gives these houses their soul.