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My basement has R-11 Kraft-faced installation already installed in the ceiling joists, stapled to the inside edge. I'm planning to install a 6 of 5" or 6" recessed lights.

What would be the best way to cut out the insulation in order to make room for the can/housing? The insulation is not as thick as the space is deep, so too much pressure will likely tear the paper or rip it out of the staples.

My top two thoughts are to try and carve out a circle with a standard knife and slide the can in with the brackets on the outside of the paper (would probably need to pre-wire before installing), or just try to cut out a section and then back-fill insulation after the lights are installed. Not sure if there's an easier trick that I'm not thinking of.

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    Is the basement conditioned (heated and/or cooled)? What's above - the heated and conditioned first floor? – Ecnerwal Dec 12 '16 at 22:53
  • The basement is half finished (and conditioned) and half not; this was for a small workshop on the unfinished side. The workshop is much colder than even the rest of the unfinished space. I will eventually finish (and condition) the rest of the basement, but the workshop will likely only get drywall on the ceiling and the rest will stay unfinished (most is pegboard walls and shelving). – Sean Dec 19 '16 at 14:03
  • Then the insulation is installed upside down. Vapor barrier in a heating climate goes to the warm side. – Ecnerwal Dec 19 '16 at 17:09
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If the basement is conditioned space, and what's above is conditioned space, the insulation is not doing much other than some possible sound reduction. (though if you don't cover it with drywall the paper may well play the role of fire hazard...)

If the fixtures ARE IC (insulation contact) rated, you can cut a hole that just fits. If they are NOT IC rated,you need to cut considerably larger hole in the insulation and remove it, not "backfill" it. You can also do that just to simplify your life if there's no significant temperature difference between the basement and the space above it.

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My question wasn’t worded well, but was primarily looking for how to physically cut the insulation. I’ve only ever cut it on the ground while compressed with a 2x4. I think the answer I was looking for, or at least what worked well for me, was scissors. I drew the outline of the light housing + attached junction box on the paper and cut it out with a utility knife. I then used scissors to cut the insulation; I kept them vertical and cut around the border of the outline going slightly deeper each time around. It went pretty fast and left a perfect fit for the light boxes.

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