I talked to Stefan yesterday morning about the details for the insulation. The big house has 5 floor (and roof) cavities, 1200mm wide, about 10.5m long, and 300mm deep. Stefan strongly suggests putting in as much insulation as possible during building, because it's quite difficult to do after the fact. He also prefers ecological insulation, but also reports that most of his clients use standard insulation.
After some math, I figured the floors and roof needed about 84 rolls of insulation. I sent emails to both the sheep's wool and flax providers I blogged about earlier, and received replies within a couple of hours.
I'm going to find out how much plain ol' mineral wool insulation costs next. My concern is that the ecological alternative, as attractive as it is, will end up being significantly more expensive. Given my well-documented concerns about the dollar, this may be an extra cost we can't bear.