GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Are these statements about wiring and insulation true?

derekr | Posted in General Questions on

First one I heard is fiberglass and rockwool insulation can sand away the wire jacket over the years from small vibrations in the house and eventually expose the wires

second thing I heard is covering your wires with insulation will cause them to overheat and start a fire. When people spray foam houses aren’t all the wires completely covered in insulation?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member


    Both are false.

    Wires in insulated walls or ceilings show no signs of wear when exposed decades later.

    The electrical code anticipates wires will be run though insulation and has rules in place (like not bundling too many) to avoid overheating.

    If you follow the code, and the way millions of other houses have been built, these aren't issues.

  2. maine_tyler | | #2

    The second one may come from the idea that knob and tube should not be insulated against. How true that is I don't know, but certainly it has more grains of truth than with modern wiring that is designed to be used in insulated walls.

    1. Expert Member
      Michael Maines | | #3

      Insulating cavities with knob and tube works fine until the insulation gets damp, then you get arcing and fires.

      I have heard stories that claim the heat from spray foam curing can melt the PVC sheathing on Romex, but I don't know how true they are. It's not something I have ever seen be an issue in the field.

      1. DC_Contrarian | | #4

        I would think it would melt the foam first.

        1. Expert Member
          Michael Maines | | #6

          A quick online search makes it appear that spray polyurethane foam can withstand around 200-300°F before melting, while Romex PVC sheathing melts at around 185-200°F.

  3. jamesboris | | #5

    Wow, that first claim is one of the more out there things I've ever heard in building... that is wild. I would challenge anyone to take a handful of fiberglass and see how long it takes you to rub off a Romex jacket + wire insulation. (short version: I would not worry about this!)

  4. severaltypesofnerd | | #7

    "second thing I heard is covering your wires with insulation will cause them to overheat and start a fire."

    That likely comes from misinformation on Knob & Tube (K&T) wiring, from people who don't understand the situation. If the fuse sizes match the wire sizes, K&T is less likely to overheat than equivalent modern wire.

    And attached, for how it's handled in my area.
    The issue with insulation is NOT heat, it's preventing future attic workers from electrocuting themselves because they don't know what's hidden down there.

    Be very careful "doing your own research". Expertise still has a place in our world.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |