Do I Need to Replace Knob-and-Tube Wiring in My San Francisco Home?

So, you’ve just discovered that your charming San Francisco Victorian has knob-and-tube wiring. Your inspector raised an eyebrow. Your insurance agent sighed. Maybe your electrician looked like they were about to break some bad news.

You’re probably wondering: “Do I really need to replace it?”

Let’s unpack that. Spoiler alert: it’s a bit more nuanced than a simple yes or no.

What Is Knob-and-Tube Wiring, Anyway?

Before we dive into replacement talk, let’s make sure we’re on the same page.

Knob-and-tube wiring (K&T) is an early method of electrical wiring used in homes from the 1880s to the 1940s. It involves:

• Porcelain knobs to hold the wires in place
• Porcelain tubes to protect wires as they pass through wood framing
• Single insulated wires, with no ground wire

It was considered top-of-the-line at the time. And honestly? It wasn’t bad… for the 1920s. But a lot has changed since flapper dresses were trending.

Why It’s Still Around in San Francisco

San Francisco’s housing stock is like a vintage record collection—beautiful, valuable, and sometimes a little crackly. With so many historic homes, K&T wiring is still surprisingly common. And in some cases, it’s still functioning. That’s a testament to old-school craftsmanship.

But function and safety are two very different things.

Here’s the Deal: Should You Replace It?

The short answer? In most cases, yes.

The longer answer? It depends—on your wiring’s condition, your home’s usage, and your future plans.

Let’s break it down like your favorite local DJ spinning a funky 70s remix.

What Are the Risks of Keeping Knob-and-Tube?

1. No Ground Wire = No Safety Net

Modern wiring includes a ground wire—basically a built-in escape route for stray electricity.

K&T wiring doesn’t. So, if something goes wrong—say, a short circuit—you’re at a higher risk of electrical shock or fire.

Would you drive around San Francisco’s hills with no brakes? That’s kind of what it’s like using ungrounded wiring today.

2. Insulation and Heat Don’t Mix

Back in the day, people didn’t insulate their attics and walls the way we do now. K&T needs open air to cool properly.

When it’s buried in insulation (which is super common in energy retrofits), it overheats. That’s when bad things happen.

One electrician in the Richmond District once found old K&T wires wrapped in cellulose insulation that was literally blackened from heat. Yikes.

3. It’s Just… Old

Even if the K&T wiring hasn’t failed yet, it’s pushing 80–100 years old. The rubber insulation gets brittle. The wires loosen. Rodents chew on them. (Don’t even get us started on that.)

Think of it like relying on your great-grandpa’s pocket watch to time your morning espresso. Beautiful? Yes. Reliable for modern life? Probably not.

4. Insurance Headaches

Some insurance companies flat-out refuse to cover homes with active knob-and-tube wiring. Others will charge higher premiums or require an inspection.

And if you ever want to sell your home? You can bet buyers (or their lenders) will ask about it.

When Might It Be Okay to Leave It?

Okay, we’ve made the case for replacement. But are there exceptions? Sort of.

If your K&T wiring:

• Is in excellent condition
• Hasn’t been modified or spliced into improperly
• Isn’t covered in insulation
• Isn’t heavily loaded with modern appliances

…then technically, it might not be a fire hazard today. But you’d still want to be on high alert.

Think of it like driving a classic car. You can do it—legally and sometimes even stylishly—but it takes vigilance, constant maintenance, and a little luck.

Signs Your Knob-and-Tube Needs Replacing ASAP

Here’s your red flag checklist:

• Flickering lights when appliances turn on
• Warm or discolored wall plates
• A burning smell (like hot plastic or fish… weird, but true)
• Fuses blowing regularly
• Visible cracked or brittle wire insulation
• DIY “patches” with modern wiring spliced in (often a fire hazard)

Even if just one of these applies, it’s time to call in a pro.

How Replacement Works — And What to Expect

Replacing knob-and-tube wiring doesn’t mean tearing down your entire house. Good electricians know how to “fish” new wires through walls with minimal damage.

What the Process Typically Looks Like:

1. Inspection – A licensed electrician checks the scope and condition.
2. Planning – They map out circuits, estimate the work, and figure out access points.
3. Execution – Wiring is replaced room by room. Drywall holes may be needed, but repairs are usually included.
4. Panel Upgrade (optional) – If you’ve still got an old fuse box, this is a good time to swap it for a breaker panel.
5. Permits & Inspections – Yep, in San Francisco, this is a must. And yes, it’s a good thing.

Cost Range in San Francisco

Expect somewhere between $10,000 and $25,000 for a full rewire, depending on:

• Size of the home
• Accessibility of walls and attic
• Whether a panel upgrade is needed
• How much cosmetic repair is required

Yes, it’s an investment. But so is not burning your house down.

A Real-Life Example from Bernal Heights

One homeowner in Bernal had no idea they even had knob-and-tube until a ceiling light flickered during a dinner party. Their electrician found exposed, cloth-covered wires scorched near the attic.

They ended up rewiring half the house, including a new panel. Their insurance premium dropped, their lights stopped acting haunted, and they now charge their Tesla guilt-free.

How to Talk to Your Electrician (Without Getting Overwhelmed)

You don’t have to become an electrical engineer to have a good conversation. Here are a few smart questions to ask:

• “Can you show me exactly where the knob-and-tube is located?”
• “Is it live, or has it already been bypassed?”
• “What’s your experience rewiring homes like mine?”
• “Will you help with permits and patching?”
• “Can I live in the house during the work?”

Bonus points if they bring a flashlight and crawl into your attic without hesitation.

Planning Ahead: Replace All at Once or Bit by Bit?

Some homeowners prefer to do a full rewire in one go. Others phase it out room by room—especially if they’re remodeling.

Pros of a Full Rewire:

• You’re done once and for all
• Usually more efficient (and cheaper) overall
• Easier to schedule inspections and permits

Pros of Phasing It Out:

• Lower upfront cost
• Less disruption at once
• Good if you’re remodeling piecemeal anyway

Just don’t fall into the trap of “we’ll do it next year” for the next 10 years. That’s how trouble brews.

Okay, But What About the Historical Character of My Home?

We hear you. No one wants to ruin beautiful old plaster or tear up pristine baseboards. Luckily, skilled electricians in San Francisco are used to working in period homes.

You can keep the character and update the guts—like restoring a classic car with a modern engine. The most important thing is choosing electricians who know what they’re doing.

Final Thoughts: Is It Time?

If your home has knob-and-tube wiring, think of this moment as a fork in the road. You’re in good company—plenty of homes in the area still have knob-and-tube. But that doesn’t mean you have to live with the risk.

Yes, rewiring costs money. But so does fire damage. Or insurance headaches. Or that one light switch that definitely shouldn’t buzz when you touch it.

Take your time. Get a few quotes. Stay curious, ask all the right questions—but don’t sit on it forever.

TL;DR — Here’s What to Remember

• Knob-and-tube is outdated and potentially dangerous, especially if modified or buried in insulation.
• Insurance and resale can be big problems with active K&T wiring.
• It might feel like a big step, but the benefits—less risk, better power, and more peace—are worth it.
• San Francisco electricians know how to upgrade homes like yours without wrecking the charm.

So—do you have to replace it? Maybe not tomorrow. But probably sooner than you think.