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 Can I Insulate Over Knob And Tube Wiring?

Hey Itchy

My old home has knob and tube wiring in the attic floor. There is no insulation over it and I'm am losing a lot of heat. What's the best way to insulate over knob and tube wiring?

Marcus B.
Northern Michigan

Adding insulation over knob and tube wiring can be dangerous and you have several issues to consider. While I've insulated over knob and tube wiring a in the past (only because the owner insisted) I wouldn't recommend it. They actually had plywood boxes built to completely cover the old but but live wiring and we were able to insulate over it. You would never want to directly cover it with insulation though and I'll tell you why.

Knob and tube wiring was very commonly installed in the late 1800's and for the first half of the 1900's. 

It consists of porcelain knobs and porcelain tubes to which the wiring attaches and passes through. It depends on air circulation to keep it cool and the wires are supposed to run parallel anywhere from 3" to 6" apart. That's if it's in ideal condition. I've found that most knob and tube wiring has issues over time and there are usually areas of exposed bare wire.  By covering it with insulation you will eliminate it's ability to stay cool and that can create a fire hazard.  

But wait, there's more! Did you know the National Electric Code (NEC) as mandated that knob and tube wiring be removed if there is any insulation near it. But some building codes in different areas the country will allow it depending on it's condition. In addition, if you still plan on insulating over this wiring you had better check with your insurance company. I'll betcha they will tell you they'll drop your fire insurance if you proceed. 

I know you don't want to hear this but I would highly recommend you hire an electrician to disconnect your old wiring and replace it with wiring that is safe and up to code. Then you have no worries and can add as much insulation as you desire. This is not a do it yourself insulation project and if you proceed you had better have a insulation professional take a look at it and go from there.

Related Tips and Advice:

Blowing Insulation Over Recessed Lights

Adding Additional Attic Insulation Over Fiberglass Batts

Skylight Covers To Reduce Air Infiltration


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