I am in the process of enclosing a porch and am wondering how to go about insulating the floor. Can I put plywood under the joists and fill the cavity with celulose? I know there are settling problems with celulose, but since the void would be directly below the subfloor, it seems that wouldn't matter. The crawl space under the porch is pretty tight, which is why I'm leaning this way instead of fiberglass. And I just don't like working with fiberglass.

 

Yes you can install the cellulose the way you described. You can avoid the settling by dense packing the cellulose between the floor cavities. Cellulose, unlike fiberglass, actually increases in R-Value when compressed.