My drywall ceiling developed a large crack over the last two months (after being fine for 70 years), and investigating my attic I discovered the lower layers of insulation were soggy and the drywall was wet and had a layer of mold. I plan to replace the drywall, and I have a roofer coming soon to look for the source of the water.

The problem is the attic is covered by a vapor barrier, what appears to be about 3 inches of loose fiberglass insulation, and then about another 6 inches of cellulose insulation. This is currently completely covering the knob and tube wires that run along the sides of the joists. I have seen some old questions here and discussions elsewhere that discuss the old code that knob and tube wiring should not be insulated, but my understanding is that new code allows insulation as there is no evidence of insulated knob and tube causing fires.

Even so, I would like to replace the ruined insulation with something new and ideally fire resistant like mineral wool. However, for the ~9sq ft area, I cannot rent a blower to use blown in insulation, and I don't know how I could place batt insulation around the wires. I suppose I could cut a thin strip to go between the wire and the wall, and cut around the knobs.

What is the safest way to replace this insulation, without replacing the entire knob and tube wiring or renting a blower?

  • Seems like a great time to replace that K&T with NM, and then, not have to worry about it at all. Aug 15, 2020 at 15:38
  • That would still require opening the walls, while now I only have the ceiling open. The attic is above the second floor, and the K&T is fed by a sub panel in a basement wall. I'm afraid that would be a huge job.
    – Daniel
    Aug 15, 2020 at 15:41
  • 2
    I might get a bale of blow in and transfer it to trash bags then dump in the attic, fiberglass is a insulator. If your access is large enough to get the bale up there a single bale or 2 can be done by hand I have done this on repairs in the past but if the lines are live be careful. I kneeled down on a hot line I did not see once and let’s say me and a large chunk of ceiling came through the ceiling (one good reason not to cover k&t) .
    – Ed Beal
    Aug 15, 2020 at 15:53
  • If you do bury the K&T in insulation, you may want to install little flags (taller than the insulation will be deep) along the joists (before covering it) indicating that there's K&T wiring under there. To serve as a reminder to future you, and anyone else who may get up in that attic. You don't want them getting a shock and coming through the ceiling, or worse.
    – FreeMan
    Aug 15, 2020 at 18:07


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