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Community and Q&A

Hanging lights after polyiso

kjmass1 | Posted in General Questions on

I have uninsulated floors in my master closet/laundry room as they are over an exposed porch. MassSave is going to treat it as a crawlspace and blow in cellulose between the joists, cutting through the beadboard ceiling. Instead of repairing the holes, they are going to add 2″ polyiso on top, and I’ll put new beadboard over that.

There are 2 hanging lights, as well as a dryer vent in this ceiling. What’s the best way to deal with the additional 2″ depth now? Extension screws? Or can you mount to the foam?


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  1. Expert Member
    BILL WICHERS | | #1

    Polyiso isn’t structural, you can’t really trust it to support anything. You want a long screw through the polyiso into a rafter/joist to hang weight from. If you’re using a decorative hook with a “screw-on screw” for lack of a better term, you can use a piece of threaded rod and a coupler (look in the electrical section at a box store for “strut”, there should be threaded rod couplers there) to make an extension.


    1. kjmass1 | | #2

      Can I reuse the existing flush box as is? Or move it to a surface mount?

      Light currently mounts to electrical box no pole. Guess I’m trying to figure out what I should do before they install...

  2. kjmass1 | | #3


    1. Expert Member
      BILL WICHERS | | #4

      They make “extension rings” for electrical boxes. Extension rings are like a box with no back. You mount the extension ring to the original box, and the extension ring serves to bring the edges of the box up the new finished surface level. There are also “mud rings”, which are usually used with drywall, but serve basically the same function. Which way you extend the box depends on exactly how you’re doing the installation and the type of existing box you have.

      If your light is heavy, try to mount the nipple (the threaded tube the fixture wires go through) to the original box for maximum strength. If this is not possible, I like loop a piece of steel wire through a hole in the original box and the mounting flange for the nipple. The steel “safety wire” is just a little extra insurance against a heavy light coming loose and falling.


  3. kjmass1 | | #5

    Great thanks. I’m hoping the dryer vent has a little extra slack and that I can just pull it 2”.

    1. Expert Member
      BILL WICHERS | | #6

      You can get vents with extended pieces of rigid ducting for when you need a little extra reach.


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