03:21PM | 07/12/04
Member Since: 08/25/01
5 lifetime posts

In a house that still has some old wiring, (knob and tube) is it safe to have insulation blown in?



03:49PM | 07/12/04
Member Since: 07/01/03
549 lifetime posts
I answered this last year on the Fix-It For'em at

To quote myself: Adding insulation in walls with K&T electric is acceptable PROVIDED the wiring is operating at or below its rated capacity. If you look in the fuse box and see 30 amp plus fuses the circuits the answer is no. If the circuits are properly fused at 15 to 20 amps, the wiring (usually 12/2) is operating within its rating and will not generate hazardous heat. The insulation itself does not support combustion and has ammonium sulfate which acts to supress compustion. Still, you should not install it where the possibility of a hot over loaded circuit exists.

Keep in mind too, that adding insulation will make later wire routing more difficult assuming you want to upgrade to modern sheathed electrical cable wiring.

End of quote

One other point, insulation will make replacement of plaster walls more difficult, or at least will incerase the amount of material to dispose of. If you think you may want to rewire, upgrade plumbing or replace plaster walls in the next few years, its best to do a demolition and replace with drywall. In that case you can insulate while the walls are open.
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