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I have a full set of stairs that walk up into an unfinished attic space. The full sized access door to these stairs is in a hallway as if its a closet. Unfortunately, the max distance I have under each stair before I hit the attic-side of an interior wall (solid blue line in picture below) is only 6 inches. What is the best way to insulate this under the stairs so heat isn't lost from the interior closet pictured? I've drawn a diagram below:

side view of access and stairs up to attic

One idea I have is to add rigid foam on the inside of the closet as FreeMan has recommended. But what can I add to the big void under the first 3 stairs and what about the small area behind the higher stairs?

Here is a close up shot of under the bottom 3 stairs. The prior owner put light insulation in place with the face on the inside of the attic and barely any insulation to fill the giant void:

enter image description here

I'm wondering if I put faced insulation against the drywall of the closet. If so, how do I secure it? There are no lumber beams to staple to. Then in front of that I loosely stack a few batts of unfaced insulation to fill up the big void?

If you are curious about the sides of the stairwell going up to the attic: they are insulated with fiberglass insulation in the wall beams and then a 2-3" rigid foam insulation in front. So when I walk up the stairs the sides are shiny silver like I'm walking into a spaceship.

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  • Do you have access to the voids under the stairs? A photo or two would really help here. Details matter.
    – isherwood
    Nov 16, 2021 at 22:21
  • I would combine both DMoore's answer and isherwood's answer. Insulating the door to stop cold air from passing the door and falling down the stairs, then an additional layer of insulation inside the closet to protect against any that does get past the door. Belt-and-braces approach.
    – FreeMan
    Nov 17, 2021 at 18:43
  • I've updated my question ht more details. I hope this helps.
    – J Dilly
    Nov 16, 2022 at 19:31

2 Answers 2

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I'd consider adding 2 inches of foam board to the closet ceiling, then drywall. Finish as desired.

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Best way is to add a door at the top to stop airflow and add insulation to that door. On the other side - insulate the door leading up to the attic. There are cheap door insulation kits sold for doors leading to garages... same thing here.

If you don't go the route of stopping drafts I would insulate door and add padding and carpet to stairs. Stairs notoriously let in air. Some cheap carpet would not only insulate but be an air stop.

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  • This assumes that the sides of the stairwell are insulated. I suspect they're not.
    – isherwood
    Nov 16, 2021 at 22:20
  • @isherwood - yes.. I expect that the basics would be done like just the basic attic insulation. Answer was for more beyond that.
    – DMoore
    Nov 16, 2021 at 22:56
  • Add a door to the top is not an option based on the layout and space available.I have updated the question to clarify that the side walls of the stairwell are insulated with insulation in the wall cavity as well as a layer of rigid foam.
    – J Dilly
    Nov 16, 2022 at 19:44

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