I know that code says no cellulose insulation with knob and tube wiring because of possible heat build up. I also know that evidence of it causing fires because of this is scarce and a few states allow cellulose if an electrician says it's in good shape.
As I air seal the attic before adding insulation there are about 10 knob and tube wires running above the kitchen ceiling, which is attic floor behind a kneewall. They were covered in blown fiberglass for probably the last 24 years.
I am having 2 different electricians come to give their recommendation and/or estimate of it it should be changed. However, since the wires come up an outside wall that's had spray foam for 8 years, go across the attic floor for about 10 feet and then disappear under a finished floor I don't see how replacing them is really that possible.
I'm going to see what the electricians say but I'm wondering about putting a piece of drywall a couple of inches above the wires, and boxing in the sides as well. That way it would be just like they are in an empty wall cavity except for the fact that there is insulation on one side and it's a ceiling cavity instead.
Thoughts?
Best Answer
Code doesn't say that anymore, at least not in WA and OR.
Serious study was done on the question of whether blown insulation on K&T was really having an impact on house fires. The studies determined it was not. And so states have been rescinding their laws against blown insulation with K&T.
Of course AFCI is a magic bullet that intercepts many wiring faults, and I would put it on any K&T.
Sometimes K&T has problems with neutrals being crossed among several hots -- that was Wrong then, just as it is wrong now. However MWBC is a method where two hots share 1 neutral, and that was legal then, and it's legal now. The hots simply must be put on opposite poles, and the breakrs handle tied. Regardless, some of the newest AFCIs don't care about shared neutrals, but apparently only from certain makers.
If the house has blown insulation, you might downbreaker one size, merely out of an abundance of caution.
Other than that, I would continue to use it indefinitely.