That spray foam is nice but it's EXPENSIVE!! The house designs I looked at use a "false" wall that is spaced a foot in from the real one. Then you fill inbetween with loose fill cellulose and do the same thing on the ceiling. The only major design differences I saw were that you have to access the attic from outside the house, no recessed lighting fixtures, an insulated slab and I would have to pile more than a foot in the ceiling so that I could refill the walls as they compact down a bit.