My home is insulated on the floor of the 2nd story crawl spaces with that spay-in insulation that looks like mouse nest. When re-wiring, several wires ( 12-2 NM-B ) will be in direct contact with this insulation while passing through the sole-plates.

It may also be in contact when running parallel with joists. I will also need to run some of the wiring under the floor of the second-story rooms between said joists, which will also submerge the cable in this insulation, although I may run this cable in conduit due to securing issues ( roughly 7-10 ft where I won't be able to reach the wire to secure with staples ).

Is "Romex" approved for contact with insulation. Would this be a fire hazard, or cause any overheating issues that would call for derating?

Thank you.

Romex has no restriction to being in contact with insulation. You can also fish or snake Romex and not need to worry about supporting.

If you were to run a bundle of cables together, whether in insulation or not, the cables would need to be derated.

The wiring that cannot be embedded in insulation is the old Knob & Tubing type. Maybe this is where you question is coming from?

You can also fish or snake Romex and not need to worry about supporting.


Hmmm... I had intended to secure the wire as much as possible, be it vertical between-the studs runs or horoziontial runs between the joists. I believe the cable is supposed to be supported within 8-12" of the device box, but it was my feeling that this was not enough for the entire run up the wall into the crawl-space ( roughly 5ft from the outlet to sole-plate ). Are you saying that the support at the device box and the last support above the sole-plate would be sufficient?
I can see it not needing support just laying between the joists under the upstairs rooms... I'm just very anal about that sort of thing. I like to be neat, and assume the worst case scenario will happen.

As far as the insulation question and NM... I figured it was approved, just wanted to be sure. Better safe than sorry.

TK, your incredibly helpful. Thanks a ton.

If your fishing the cable through voids, no need to support the cable.