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What Knob and Tube Rewiring Actually Costs
- matt49401
- Jun 9
- 6 min read
The Letter Nobody Wants
You open the envelope. It's from your insurance carrier. Non-renewal. Reason: knob and tube wiring.
Now you need a number. A real one. Not a "we'll need to come out and take a look" number — the kind every contractor gives you before they'll quote anything. You need to know if you're looking at $20,000 or $75,000, and you need to know today, because your policy expires in 60 days.
This article gives you that number. We'll cover what knob and tube replacement actually costs in San Francisco, what drives the price up or down, why most estimates you'll receive are wrong, and how to get a property-specific range in 30 seconds.
What It Actually Costs
In San Francisco, knob and tube replacement typically costs $25,000–$75,000 for a full single-family home rewire, or roughly $20 per square foot.
That range is wide for a reason — and we'll get into why in the next section. But here's how it breaks down by home size for a typical Bay Area property:
Home Size | Low End | Typical | High End |
1,000 sq ft | $20,000 | $30,000 | $42,000 |
1,500 sq ft | $30,000 | $40,000 | $58,000 |
2,000 sq ft | $40,000 | $50,000 | $65,000 |
2,500+ sq ft | $45,000 | $60,000 | $75,000+ |
These numbers include the full scope most homeowners actually need: rewiring, code-compliant outlets and switches, permits, inspections, and wall and ceiling patching. They do include floating to match the wall texture and spot paint to match the existing color.
"I've quoted hundreds of these projects across the Bay Area. Two homes on the same block can be ten thousand dollars apart, and it has nothing to do with the contractor — it has to do with the ease of which we can rewire a home. Attics, garages and crawl spaces provide areas where we can fish new ROMEX. If these areas are not available, then we’ll make many more holes to fish through the walls." — Matt Ticknor, Founder - Knob & Tube Replacement
The Four Variables That Move the Number
Four things determine where your project lands inside that range.
1. Square footage — but not linearly
Older San Francisco homes have more interior walls per square foot than modern construction. A 1,500-square-foot Victorian with three bedrooms and a formal dining room costs more to rewire than a 1,500-square-foot open-plan loft. More walls means more wire pulls, more outlets to bring to code, more patching.
2. Whether you need a new electrical panel
Many homes with knob and tube wiring also have undersized or outdated panels — sometimes still operating on 60-amp service when modern code expects 200. If your panel needs to be upgraded as part of the rewire, add $3,000–$8,000 to your project.
This is also the single most common cause of "surprise" change orders mid-project. A thorough estimate accounts for the panel up front.
3. Wall and ceiling type
Plaster-and-lath construction — common in San Francisco homes built before 1950 — is meaningfully harder to work in than modern drywall. Cuts are messier, patches are more skilled work, and the labor hours add up. Expect a 15–25% premium on a plaster-and-lath home compared to drywall.
4. Access
Can the crew reach wire runs through an unfinished basement or attic, or do they have to open finished ceilings on multiple floors? Access changes everything. A home with an open basement and a walkable attic can come in at the low end of the range. A home with finished ceilings throughout pushes toward the high end.
This isn't an academic discussion. According to the National Fire Protection Association, electrical failure or malfunction factors into 45,000 to 55,000 home structure fires every year, and 63 percent of those involve wiring and related equipment. The cost of getting it right is real. The cost of getting it wrong is worse.
Why Most Estimates You Get Are Wrong
Here's the part nobody in this industry wants to say out loud: most of the quotes you receive aren't comparable.
Three reasons:
The "electrical-only" trap. Many electricians quote the wire pull and nothing else. No patching. No painting. No permits. No final inspection coordination. By the time you've paid the drywall contractor and the painter separately, you're $8,000–$15,000 over the original estimate.
The "we'll find out" estimate. Some contractors deliberately quote low to win the job, then issue change orders once walls are open. You're locked in by then.
The missing panel. A quote that doesn't address whether your panel can carry the new load is incomplete. If it needs to be replaced, it will be — the only question is whether you knew that going in.
"A $15,000 quote and a $45,000 quote for the same house aren't the same scope. One of them is going to call you in week two with a change order. Ask every contractor what's included after the wires are pulled — patching, painting, permits, panel. That's where the real number lives." — Matt Ticknor, Founder - Knob & Tube Replacement
When you compare bids, line them up against the same scope. If one contractor's number is dramatically lower, the question isn't whether they're cheaper. The question is what's missing.
The Insurance Reality in California
The reason most of our calls now start with an envelope is that California's home insurance market has changed. Carriers are non-renewing knob and tube homes aggressively, and they're doing it earlier in the policy lifecycle than they used to.
ABC7 News reported on the trend last year, quoting Bay Area insurance broker Jerry Becerra: "If we put it on the application, we are going to get declined."
The same investigation featured me walking a reporter through what underwriters actually see when they look at knob and tube — degraded insulation, ungrounded circuits, and a system that was never designed for the electrical loads of a modern home.
What this means practically:
If you're buying: lenders won't approve the mortgage without insurance, and most standard carriers won't write a policy with active knob and tube. Your options are the California FAIR Plan (significantly more expensive) or rewiring before close.
If you already own: non-renewal notices are increasingly common, and they typically give you 60–90 days. That's enough time to rewire if you act quickly — but only if you act quickly.
If you're selling: appraisers may downgrade your home's value, and offers will come in lower from buyers who've done the math on what the rewire will cost them after they take possession.
The insurance market is unlikely to soften. If you have knob and tube wiring, addressing it is no longer optional in California — it's a question of timing.
How to Get a Real Number in 30 Seconds
The ranges above are useful for orientation. But your home isn't a range. It's a specific property with specific square footage, a specific construction era, and a specific scope.
That's why we built the knob and tube pricing tool on our homepage. Three steps:
Enter your property address
The system pulls your square footage from public property data
You get a real-time estimate based on our actual pricing model — the same one we use internally
The estimate is a preliminary range. Final scope and pricing are confirmed following a review or on-site inspection by our team. But it's a real number, generated from the same logic our estimators use, in less time than it takes to leave a voicemail.
Frequently Asked Questions
How long does knob and tube replacement take?
A typical full-home rewire takes 15–25 working days from permit to final inspection. Smaller homes with good access can finish in under two weeks. Larger homes with plaster walls and finished ceilings throughout can run four weeks or more.
Can I stay in my home during the rewire?
Sometimes. Single-floor homes or projects we can phase room-by-room often allow you to stay. Whole-house rewires with active work on every floor usually require 7–10 days of temporary housing. We're honest about which situation you're in during the initial evaluation.
Will insurance cover the cost of replacement?
Almost never. Standard homeowners policies don't cover proactive electrical upgrades, even when the upgrade is required to maintain coverage. Some carriers offer credits on future premiums after a documented rewire, but the upfront cost is yours.
Does knob and tube wiring need to be replaced if it still works?
If you want standard homeowners insurance in California, in most cases: yes. The wiring may still carry current safely within its original design limits, but insurers treat it as a fire liability regardless. Working knob and tube and insurable knob and tube are no longer the same thing.
How do I know if my home has knob and tube wiring?
The easiest place to look is an unfinished basement or attic. You'll see white porcelain knobs nailed to wood joists, with single insulated wires running between them through porcelain tubes drilled through studs. If your home was built before 1950 and you've never had it fully rewired, assume you have at least some active knob and tube somewhere in the structure.
Have a property you'd like a real number on? Click here to get your estimate in 30 seconds →
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