What is Knob and Tube Wiring?

Posted by Krista Fracke on Thursday, December 1st, 2016 at 2:42pm


If you are buying an older home, doing a home inspection is always important. You need to know what’s lurking behind those walls, especially when it comes to your electrical. If your inspector comes back with the report letting you know that you’ve got Knob and Tube, you may have yourself a real problem. Let’s discuss.

What is knob-and-tube wiring?

Also called K&T, is a very early type of electrical wiring that was installed during the 1880s until the 1930s. It was eventually displaced as the cost of installation was high and is only allowed in very rare cases in new installations.


What is the problem with it?

Most homebuyers who find out that they have knob and tube wiring will opt to replace it. The reason for this is that modern household have higher power requirements than what the old wiring can handle. Some homeowners who found out this problem the hard way, instead replaced blown fuses with fuses that were rated for a higher current, which causes overfusing of the circuits. What does this mean? Well, it basically puts your home in danger of heat damage and/or fire. No one wants to buy a home where there is the potential for fire right off the bat, so replacing the knob and tube system is a must.

As well, with knob and tube wiring being so old, the chance of it being damaged is highly likely. Damage from renovations or rodents is likely, but so is damage from previous carelessness of homeowners who hung objects from the fragile wiring. If it has cloth and rubber insulation, this can also because dry and brittle and break over time.

Another issue with knob and tube wiring is that it needs the surrounding air to let heat dissipate, so loose, blown-in or expanding foam insulation is not allowed around the wiring, according to the National Electrical Code. This means your home will not be very energy efficient and any upgrades your home may require to make it that way will ultimately lead to you having to replace the wiring.

What does it cost to replace knob and tube?

Depending on the size of your home, replacing knob and tube wiring will run you in the thousands of dollars, and even up to $10,000.

Should I buy a home with knob and tube?

The choice is ultimately up to you. If you find that the home you love has knob and tube, you can choose to ask the seller to amend the offer to include the cost of replacing the wiring. If they refuse, you need to decide if you have the time and the money to do the replacement.

If you need any help finding a new home, I’m always available.

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