Portland has a lot of beautiful old homes. Craftsman bungalows from the 1910s. Victorian houses from the 1890s. Four-squares and foursquares from the early 1900s in neighborhoods like Irvington, Ladd’s Addition, and Sellwood. These homes are genuinely special. They are also homes that very often have knob-and-tube wiring somewhere inside the walls.
If your inspector flags knob-and-tube wiring, here is what it means and what to do about it.
What Is Knob-and-Tube Wiring?
Knob-and-tube was the standard residential electrical wiring method from roughly the 1880s through the 1940s. It uses two separate conductors: a hot wire and a neutral wire. These wires run through the framing of the house, supported by ceramic knobs where they are nailed to the framing and protected by ceramic tubes where they pass through framing members.
The wiring itself is single-conductor copper wire with a cloth or rubber insulation jacket. There is no ground wire. The system does not have the third grounding conductor that modern wiring requires.
In Portland’s older neighborhoods, you can often spot knob-and-tube in the attic or basement where it is exposed. The distinctive white ceramic knobs hold the wires away from framing. The ceramic tubes protect the wires where they pass through holes in joists and studs. The wires themselves are usually black and white with a cloth braid outer jacket that is often brittle and cracked in older installations.
Why Is It a Concern?
Knob-and-tube wiring was designed for homes with a fraction of today’s electrical load. A home in 1920 might have a few light fixtures and a kitchen appliance or two. Today’s homes run computers, large televisions, dishwashers, refrigerators, dryers, window air conditioners, and dozens of other devices simultaneously. Knob-and-tube systems were never designed for this load.
Several specific concerns come up regularly in inspections of Portland homes with knob-and-tube.
Insulation contact. Knob-and-tube wiring is designed to dissipate heat to the surrounding air. When attic insulation is blown or laid over knob-and-tube circuits, the wires cannot dissipate heat normally. This creates a fire risk. The National Electrical Code specifically prohibits covering knob-and-tube wiring with insulation, but many homes have had attic insulation added over the years without regard for what was already there.
Deteriorated insulation jacket. The rubber and cloth insulation on century-old wiring becomes brittle and cracks over time. When the insulation jacket breaks down, the wire is exposed. Exposed conductors in contact with each other or with combustible framing materials are a fire hazard.
Improper splices and extensions. Over the decades, many knob-and-tube systems have been extended, modified, and spliced by people who were not electricians. The connections are sometimes made in wall cavities with no junction box, or made with mismatched materials. These improper modifications are some of the most dangerous aspects of knob-and-tube in Portland homes.
No grounding. The lack of a grounding conductor means all outlets on knob-and-tube circuits are two-prong only. If the home has been updated with three-prong outlets, they have either been improperly connected to knob-and-tube (which creates other problems) or they are ungrounded three-prong outlets that offer no actual grounding protection.
What Insurance Companies Say
Insurance carriers view knob-and-tube wiring unfavorably. Many will not write a new homeowner’s policy on a home with active knob-and-tube. Others will write coverage but charge a higher premium or require the wiring to be replaced within a specified period after closing.
Before you close on a home with active knob-and-tube, call your insurance agent. Find out exactly what your carrier requires and what your premium will be. This information belongs in your buying decision and your negotiation.
Active vs. Abandoned Knob-and-Tube
Not all knob-and-tube wiring in a home is necessarily still active. Many Portland homes have had partial electrical updates over the decades. Parts of the house were rewired with modern wiring while other areas were not. Sometimes the old knob-and-tube circuits were de-energized and abandoned in place as new circuits were added.
The distinction between active and abandoned matters a great deal. Abandoned knob-and-tube with no current running through it is a cosmetic and documentation issue. Active knob-and-tube carrying current is the safety concern.
A thorough inspection documents which knob-and-tube is active, which appears abandoned, and what condition the active portions are in. That information tells you the scope and cost of what needs to happen.
What Rewiring Costs
Full rewiring of a Portland-area home typically costs between $8,000 and $20,000 or more depending on the size of the home, the complexity of the existing layout, and whether the panel also needs upgrading. This is a real cost that belongs in your negotiation if the home has active knob-and-tube throughout.
Partial rewiring of specific circuits is less expensive but only makes sense if most of the home has already been updated and specific areas remain. If the entire home is knob-and-tube, partial rewiring rarely makes financial sense compared to a full update.
Portland Neighborhoods Where Knob-and-Tube Is Common
Knob-and-tube is most common in homes built before 1945 in the close-in Portland neighborhoods: Northeast Portland, Southeast Portland, Sellwood, and the historic areas of Oregon City. It also shows up in older established neighborhoods in Vancouver and other Clark County communities where early 20th century housing stock remains.
If you are buying a home built before 1950 anywhere in our service area, assume knob-and-tube may be present until the inspection confirms otherwise.
Have questions about an older home you’re considering? Schedule your inspection or call Russ at 971-202-1311 seven days a week.