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Community and Q&A

Cellulose Insulation Over Ceiling Light Junction Boxes

etting | Posted in Mechanicals on

My house will be lit with flush-mounted ceiling lights that connect to Romex cables through round blue plastic junction boxes.   Each one takes one 100-watt bulb.  I will use LED bulbs, but a future owner might use incandescent.   I spent a few hours today trying to find out whether I need to install anything to create a separation between the junction boxes and the cellulose attic insulation I will blow in.  Virtually everything I found related to recessed lights, which I know to avoid.  I found a couple of discussions among people of unknown expertise who mostly thought the cellulose can sit right on top of the junction boxes.  The one article I found that said anything that might answer my question is this:

“The NEC has specific rules regarding clearance around recessed lighting fixtures. Thermal insulation must be installed a minimum distance of 3 inches from any recessed lighting fixture, wiring compartment or ballast. Additionally, the insulation cannot be installed above the fixture in a way that would trap heat and prevent air circulation. There are no specific regulations regarding what type of material to use when protecting fixtures. The protection must remain in place after blowing the insulation.”

This too seems to refer mostly (or perhaps entirely) to recessed fixtures, but its wording could also mean that one must have 3 inches around a recessed wiring compartment.

I found a helpful video here about how to air-seal a junction box like the ones I’m using, and it doesn’t say anything about creating a separation from the cellulose, but I don’t want to make any risky assumptions:

How to Air-Seal a Ceiling Electrical Box in an Attic

Will air-sealing the junction box be sufficient, or if I need a 3-inch (or greater) separation from the cellulose, what do you recommend for creating it?

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  1. walta100 | | #1

    Yes the blue box is allowed to come in contact with the insulation.


    1. etting | | #2

      Thank you, Walter. I was afraid this question was so basic, no one would bother to answer it, which is probably why I couldn't find any authoritative answer after hours of searching.

      1. Expert Member
        MALCOLM TAYLOR | | #3


        I would look at is as: If the light fixture is designed to be installed into a standard plastic junction box, it doesn't need any extra protection or separation from combustibles.

        1. etting | | #4

          That's very helpful, Malcolm. Thank you.

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