Knob-and-Tube Wiring in Seattle-Area Homes: What to Know

What knob-and-tube wiring is

Knob-and-tube was a common way to wire homes in the early part of the twentieth century. Instead of a single cable holding several wires, it uses separate hot and neutral wires strung through the house. Ceramic knobs hold the wires away from framing, and ceramic tubes protect them where they pass through joists and studs.

Many older homes in Seattle, Shoreline and nearby neighborhoods were built during that era. Some have been fully rewired, some partly, and some still have original circuits in use.

Why it becomes a concern as it ages

Knob-and-tube was a reasonable system when it was installed. The problem is age, modification, and the demands of a modern household.

• No ground wire, so it cannot properly protect three-prong devices or provide a path for fault current
• The original cloth and rubber insulation becomes brittle and can crack or fall away, especially where it has been disturbed
• It was designed to shed heat into open air; when it is buried in attic or wall insulation, it can run hotter than intended
• Decades of amateur splices, extensions and connections to newer wire are common and often hidden
• Original circuits were sized for a few lights and small appliances, not today's kitchens, electronics and space heaters

How to spot it

You can often find signs of knob-and-tube without opening any walls. Look, but do not touch the wiring, and do not pull at insulation around it.

• In an unfinished basement or attic, look for single wires running on white ceramic knobs or passing through ceramic tubes in the framing
• Two-prong outlets throughout the house, especially in older rooms
• Old push-button light switches
• Cloth-covered wires visible near light fixtures, in the basement, or at the panel
• An older fuse box, or a newer panel with older wiring feeding some circuits

Partial vs. full rewire

A partial rewire replaces the knob-and-tube circuits that remain while keeping wiring that has already been updated. It makes sense when an inspection shows only some circuits are original and the rest are in good shape.

A full rewire replaces the home's wiring throughout, often along with outlets, switches, and sometimes the panel. It is usually the better choice when knob-and-tube is widespread, when the home has a mix of old and patched wiring, or when you are already planning a remodel. Either way, a licensed electrician pulls the permit, and the work is inspected.

Insurance and home sales

Many insurers ask whether a home has knob-and-tube wiring, and some may want an inspection or a plan to replace it. If you are buying or selling an older home, it often comes up during the home inspection.

If you have questions about your own policy, ask your insurance agent directly. An electrician's inspection gives you a clear picture of what is in the walls, which helps with both conversations.

What to do if you have it

Do not add insulation over knob-and-tube wiring or extend its circuits until a licensed electrician has evaluated it. Avoid overloading those circuits with space heaters or large appliances.

All City Electric is a family-owned, licensed and insured electrician that has worked on homes across King and Snohomish Counties since 1971. Call (206) 533-6333, Monday through Friday, 8:00 to 4:30, to set up an inspection.