If you are buying or already own an older home in Portland, you may have heard your inspector mention knob and tube wiring. It sounds technical, but the concept is simple. Here is a plain-English explanation of what it is, why it matters, and what your options are.
What Is Knob and Tube Wiring?
Knob and tube is an older style of electrical wiring that was standard in homes built roughly between 1880 and 1940. You can identify it by two features. The wires run through small ceramic tubes where they pass through wood framing. They rest on small ceramic knobs where they are attached to the framing. This is where the name comes from.
Knob and tube does not have a ground wire. It uses two wires: one hot and one neutral. Modern wiring systems use three wires, adding a ground wire that provides a safety path for electricity in case of a fault.
Is Knob and Tube Dangerous?
The wiring itself, when original and in good condition, is not necessarily dangerous. The problems come from what often happens to it over the decades.
Improper modifications are the biggest risk. Many homeowners or unlicensed electricians have spliced newer wiring into knob and tube systems over the years, sometimes using methods that create real fire hazards. Insulation contact is another serious issue. Knob and tube needs air circulation around the wires to dissipate heat. When insulation is blown into attic spaces and ends up covering knob and tube wiring, heat builds up and can become a fire risk. Overloaded circuits are also common, as older homes were built for far less electrical demand than today’s households put on them.
What Will My Inspector Note?
We will document the presence of knob and tube wiring. We will note whether it appears to have been modified, whether it is covered by insulation, and whether there are signs of overheating or improper repairs. We will likely recommend evaluation by a licensed electrician.
What Are the Real-World Consequences for Buyers?
Some insurance companies charge higher rates or refuse to insure homes with active knob and tube wiring. This is worth checking with your insurance agent before closing. Some loan types, including certain FHA and VA loans, may require that knob and tube wiring be addressed before the loan is approved. If you are using a VA loan, see our military discount page for more information. If you plan to add insulation or do any electrical work, knob and tube needs to be part of the conversation with your electrician.
What Does Rewiring Cost?
A partial rewire addressing the most problematic areas typically costs $3,000 to $8,000. A full rewire of an older home can range from $10,000 to $20,000 or more depending on home size and complexity. This is worth factoring into your purchase offer negotiations.
Buying an older Portland home and want a thorough electrical evaluation? Schedule your inspection here.