I am planning to add additional blown-in insulation to my attic space. Currently there is about 5" of old cellulose insulation. I plan on raising this to around 15" to achieve a rating of R50. I will no longer be able to see the joists after adding this additional insulation. I am aware of this being an issue for moving around in attic. My question is, should I keep the insulation contained to each space between joists (rafter bay, if that's what you call it)? I could use netting, plywood or foam board if need be.

  • If you use plywood to build up the sides of the joists to contain the insulation, then you still won't be able to walk across them.
    – SteveSh
    Commented Dec 9, 2023 at 15:24
  • Heh, good point @SteveSh. The barriers could become somewhat of an annoyance or hazard.
    – qq4
    Commented Dec 9, 2023 at 17:00

1 Answer 1


No. Covering the joists improves your overall insulation, since wood is not a particularly good insulator, and netting/barriers/etc will just make it even harder to move around.

Just bury the joists. If there are places you need to go on a regular basis, screw down catwalk boards. If you go there a LOT, make an elevated catwalk.

Otherwise, take a snow shovel with you and wear a dust mask for the rare things where you need to get somewhere to run a cable or check a leak or whatever. Rake the insulation you shovel aside back in place when the task is done.

  • I think blown in insulation is a PITA just for the reasons you mentioned. It's a lot easier to move a fiberglass batt or roll out of the way, then put it back.
    – SteveSh
    Commented Dec 9, 2023 at 15:26
  • Yeah, I would sister some taller joists (doesn't need to be full length, and doesn't need to be flush with bottom of existing joists--can be vertically offset) anywhere you plan to walk, and put a catwalk after blowing in the insulation.
    – Huesmann
    Commented Dec 9, 2023 at 20:35
  • @Huesmann, crossframing (with blocking in every other opening) would be significantly cheaper and easier than sistering.
    – popham
    Commented Dec 9, 2023 at 20:51
  • @SteveSh given how rarely one needs to go, and how much better a job of blocking air leaks cellulose does than batts, I don't consider a little snow shovel / rake relocation of cellulose a big deal. And it doesn't make me itch.
    – Ecnerwal
    Commented Dec 9, 2023 at 22:33

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