WHAT IS KNOB AND TUBE?
Knob and tube wiring was one of the first styles of residential electric wiring, and was common until the 1950s — it uses ceramic “knobs” and “tubes” to hold the wires in place, with the hot wires (black) and neutral wires (white) running separately. There were no ground wires in this style of wiring. (A nice description and photo are available at http://www.knobandtubewiring.com/ )
While once standard, it has been considered obsolete for quite some time, and much of it has been upgraded to modern wiring, in which the hot, neutral, and ground wires all run togetherwithin plastic sheating. Knob and tube wiring is considered a potential fire and safety hazard because the black and white wires could make contact relatively easiliy, and the rubber and cloth insulation does break down over time.
COULD IT STAY?
While I did find a couple of sources that said it was fine to insulate over knob and tube wiring, the overwhelming majority advised strongly against doing such a thing. And really, since it needed to be upgraded sooner or later, it would be much easier to get at while the attic was still easy to get around in (pre-insulation). I would have to hire an electrician before embarking upon my insulation project — even if I were qualified, state regulations don’t allow me to do electrical or plumbing work on my rental property.
THE ELECTRICAL UPGRADE
While I usually go through a process of interviewing and getting bids from at least 3 contractors, this time was an exception — after coming down from the attic one afternoon (investigating what would have to be done for insulation), I found that an entire circuit of lights and outlets no longer functioned in the upstairs apartment. The knob and tube wiring was apparently so fragile that I must’ve bumped it and caused it to short out. Not good, no matter how you look at it. I shut off that fuse and hired a general contractor that I’d used for past projects — I had a working relationship with her so she was able to come out right away. I was able to save cost by taking down all of the affected light fixtures, outlets and switches myself.
$1500, three days, and several areas of repaired plaster later, my rental unit was outfitted with modern wiring. (Except for a couple of “forgotten” non-functional outlets that I had to call them back out to fix later. Doesn’t seem like that sort of thing should really be happening.) Thankfully, the tenants were very patient with having workers in their apartment for a few days — I think that they were a little worried about the electrical situation when I explained it to them (I was too), and felt a lot safer with the upgrade. As well they should. And with the new wiring in place, I was set to start sealing up the ductwork that ran throgh the attic, as well as the air leaks and attic bypasses — a lot more work needed to be done before insulation could start going in.