Can loose fill, blown fiberglass be netted and blown as cavity insulation in a flat, unvented roof assembly ?

I've been struggling to define the roof insulation strategy for my new ICF house in southern New Mexico, and am interested in any input. It will be a flat roof (1/12 slope trusses). I'm convinced I want to use an unvented "attic". I think I understand the objectives of either controlling condensing surface temps (rigid board insul above deck), or providing an air-impermeable insulation (e.g. CCSPF under deck).

My preferred approach is to use some reclaimed Polyiso board on top of the roof deck if I can source it locally (possibly with some additional cavity insulation). The second alternative I'm considering is 1 inch of CCSPF applied under the roof deck as an air barrier, and then some cavity insulation.

So, as I noted, my question is, can loose fill, blown fiberglass be netted and blown as cavity insulation in this configuration? The energy rater I'm working with didn't think it was feasible due to the risk of settling and a gap occurring between the insulation and roof deck. I've heard of other local builders using the CCSPF approach and securing batts with wire to the underside of the deck, but I'm not convinced this is a great stategy. I would like to apply netting at the bottom of the trusses, and just fill them up with inexpensive blown fiberglass. I've seen an example of cellulose in such an application (Building Science Digest 102, photograph 3). I'm hesitant to use cellulose due to the potential weight, and potential consequences from a water leak in the flat roof. I've read of JM Spider being blown wet with an adhesive overhead but haven't found a local contractor that has the equipment.

Any thoughts are appreciated!

I didn't follow - what is the problem with a small gap between settled insulation and the roof deck?

Jonr, I'm not sure. The 2009 IRC section 806.4 on unvented attics states: "The air-permeable insulation shall be installed directly under the air-impermeable insulation." I imagine the words "directly under" is the issue. As long as the insulation above or below the roof deck is sufficient to prevent condensation, I'm not exactly sure why it would matter much.



From a heat conduction perspective, I can't see how a gap would effect the overall heat transfer from the outer roof surface all the way to the interior ceiling surface.

Perhaps they are trying to prevent a semi conditioned sealed attic, with insulation on the floor and also in/above the rafters.