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insulate behind recessed lighting in sloped ceiling

mgensler | Posted in Green Products and Materials on

We are removing the 6″ recessed lights from our sloped ceilings. We have been able to pull the pieces of the old lights through the 6″ hole. The builders didn’t insulate behind the lights so we are looking to fill in. It’s approximately 15″ x 24″. We will then put in an air-tight, ic-rated led and rope caulk the flange to the ceiling to create an air-tight seal. We can stuff fiberglass in the hole ok but were hoping to find mineral wool or something similar to it that is flexible and doesn’t break into chunks.

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  1. Expert Member
    BILL WICHERS | | #1

    What kind of insulation is in there now? My first thought would be to try to match what's already there.

    If you just want to stuff something in there, I'd absolutely go with mineral wool. You can't do much about any potential mositure issues with a roof assembly when all you're doing is backing some insulation into a 6" hole for a light, so it's not worth worrying about all the fancy stuff. Try to seal the hole as best as you can for air tightness. Mineral wool will be the least likely of the fluffy insulation materials to give you trouble.

    If you buy mineral wool batts, you can rip chunks out with your hands to make it "stuffable". I've done this many, many times when firestopping holes commerically. I wouldn't use the loose-fill mineral wool for this because it's actually too loose here -- it won't want to stay in the hole. The batt material is a little more dense, and it will be less likely to try to fall out while you're working.

    Note that I wouldn't try to cut a round piece to insert through the hole. I'd rip chunks out of the batt with my hand, then stuff those into the hole until it felt reasonably full and void-free. If you have a vent channel above the existing insulation, try not to overfill the hole and block the vent channel by mistake.


  2. mgensler | | #2

    Thanks! There is R30 faced fiberglass in the rest of the ceiling. I wasn't sure if having the paper touch the LED fixture was the best idea hence my thoughts on trying to use mineral wool. Maybe I can install R13 unfaced fiberglass first and then the rest with mineral wool chunks. That would keep the mineral wool from falling down the air vent channel.

    1. Expert Member
      BILL WICHERS | | #3

      If you use an "IC" rated (Insulation Contact) fixture, then you're OK if the insulation contacts the fixture. What you want in a top-floor ceiling is an "IC-AT" rated fixture. "IC" is "Insulation Contact", "AT" is "AirTight".

      In my own experience, "airtight" is wishful thinking, it should really be "leaks less". It's still worth some effort to air seal an AT rated fixture.


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