Download PDF version (211k) Log In or Register to view the full article as a PDF document.
Q.I am remodeling a 1920s house that has the original knob-and-tube wiring. I would like to blow cellulose into the stud cavities but am guessing that it's not safe to do that with the exposed wiring in the cavities. What does code say?

A.Rex Cauldwell responds: You're right; it isn't safe. The reason is that knob-and-tube wiring is designed for open-air heat dissipation. That means there cannot be insulation around the wires, which would be the case if you blew cellulose into the wall cavities.

The same applies for knob-and-tube wiring in the attic or between floor joists. You shouldn't have any insulation around the wiring — not even fiberglass.

Rex Cauldwell is a master electrician in Rocky Mount, Va., and author of Wiring a House.