Insulation – Spray Foam vs. Rigid Foam – GreenBuildingAdvisor

I’m looking for input on an insulation question with a new house build. Im a contractor in Upstate NY / Zone 5 in the Hudson Valley. 3000 SQ ft single level modern home. We are maybe 75% done framing it now. 

For context, the plan shows closed cell foam 6.5″ / R-49 directly applied to the underside of the roof sheathing (5/8 Zip). Low pitch roofs with rubber roofing.

 

The walls are 2×6 16″ oc with 1/2″ Zip, 3″ of closed cell foam in cavity, and 2″ of Rigid Foam directly applied to the outside of the 1/2″ Zip…. then 3/4″ furring strips, and vertical metal cladding.

The floors are the main question– maybe a third of the house (one room 28′ x 28′ and a 16′ x 16′ room both approx.) sits over concrete footers and 8″ x 8″ steel columns rather than a conventional foundation. The floor deck, which consists of flush (4) 9.5″ LVL beams (around the perimeter, and one down the middle of the floor joist span on the bigger room) and 12″ floor trusses, sits roughly 4′ above grade. 

The plans call for 5″ of closed cell foam to be applied in the floor joist cavities. 

I am attempting to advocate instead for using Fiberglass or Rock Wool in the cavities , and then use 2″ + 7/16″ Zip R sheathing, seams taped.. underneath both rooms’ floor systems. I feel like it will result in a better overall floor.

The main concern is airtightness, overall R Value, and something that works for our area. What do you guys think? 

Dropping the beams below the joists would have changed the look for the worse and was never really discussed, before anyone asks…