Systems Guide · San Francisco

Electrical Upgrades in Older San Francisco Homes: When to Rewire

By Solid Bay Construction SF | Updated 2026

Many San Francisco homes built before 1950 still have some of their original knob-and-tube wiring in service, decades past its intended lifespan. Here's how to know whether your home needs a partial upgrade, a full rewire, or just a panel replacement.

What to Look For

• Knob-and-tube wiring — identifiable by ceramic knobs and tubes visible in an unfinished attic or basement; it lacks a ground wire and its rubber insulation becomes brittle with age
• A fuse box instead of a breaker panel — a strong signal the electrical system predates modern safety standards
• A panel rated under 100 amps — often insufficient for a modern home with central HVAC, an EV charger, or an electric range
• Two-prong (ungrounded) outlets throughout the home
• Frequently tripped breakers or flickering lights under normal use

Partial Upgrade vs. Full Rewire

A panel upgrade alone (swapping to a 200-amp breaker panel) makes sense if the home's actual wiring is otherwise sound copper, just underpowered at the source. A full rewire is warranted when knob-and-tube or aluminum wiring is present throughout, since insurance carriers increasingly decline or surcharge policies on homes with active knob-and-tube wiring — this is often the real trigger, not just a functional concern.

Typical Costs

Insurance Is Often the Real Deadline

If your homeowners insurance carrier has flagged knob-and-tube wiring at renewal, or a home inspection during a refinance surfaced it, that's usually the practical trigger to act rather than an arbitrary renovation timeline. As with plumbing, rewiring during an already-planned renovation — while walls are open — is significantly more cost-effective than as a standalone project.