If we were going to have radiant on the main floor, with an above the floor deck type of system, I know we need insulation between floors.

What options are there besides fiberglass batts between the I-joist cavities? Spray foam would seem too expensive for this application.
How about 2" of foam (EPS, XPS, ISO, etc, etc) cut to fit between the joist cavities? If this was viable, how to attach the foam? Just some cap nails into the subfloor? Glued under the subfloor? Would we need to seal around the foam (between foam board and I-joist) with spray foam for good measure?
How do you handle insulation in bays where there is plumbing and other things like that?
Other options?

Thanks for any info.

Hi,

what is the space under this assembly? Heated basement, I believe, right? If so, anything that gets you an R10 or so is fine, and air sealing does not need to be perfect... when the hot is on top, you don't have much convection. make sure the ends and edges of the joists to the outside are well insulated though.

Yes, it is a heated basement. I'm really looking for other options besides fiberglass batts.
How do you insulate the rim joist cavity? We do have 1" of R board on the outside of the OSB sheathing to help somewhat with thermal bridging. We are planning on 2" of dense spray foam + insulation infill (shooting for cellulose) and I am going to ask for a quote to do the rim-joist as well. But if there would cheaper alternative, I'd like to know too. Thanks.

any foam product, spray or rigid, works fine, though if you use rigid I would get a few cans of spray foam to seal up the cracks.

in the joists, anything that insulates (real R-value) works. denim, rigid foam, spray foam are the 3 non-fiberglass options I can think of for a small R-value install.

Thanks Rob!