Why Can’t You Insulate Over My Knob and Tube Wiring?

The dangers associated with insulating knob and tube style wiring

Knob and tube is a type of electrical wiring that was commonly used in homes in the United States between about 1880 and 1940. The wiring was widely used inside wall cavities and in attics, since it was less expensive than other wiring choices. Porcelain “knobs” supported the copper wiring and porcelain “tubes” were used to pass the copper wiring through wood framing members of the home.

Knob and tube wiring depends on air to dissipate the heat it creates. In an age when attics and walls of homes did not typically have insulation, plenty of air space was available for the wiring to stay cool.  

Newer homes with modern wiring do not have this issue. Insulation can be placed directly in contact with modern wiring without risk of overheating.

In making homes more energy efficient, we find St. Louis homes on a regular basis that were originally constructed with knob and tube wiring. Sometimes those homes still have no insulation. Sometimes insulation was added later and unsafely placed in contact with the wiring thus creating a safety hazard.

Whenever knob and tube wiring is live and supplying electricity to the home, covering or burying that wiring with insulation creates the risk of overheating and possibly a fire.

Be smart about saving energy with knob and tube wiring

A home with little or no insulation can usually benefit greatly in terms of comfort and energy efficiency from the addition of insulation to the attic and/or walls. To do it safely, first the knob and tube wiring must either be removed or permanently disconnected by a licensed electrician. Then insulation can safely be added.

Could we add insulation directly over your knob and tube wiring? Yes, we could, but we wouldn’t. Now that you know why, you wouldn’t want us to. Would you?