While the foundation and framing have already received a skin of XPS, i've spent dozens and dozens of hours debating how to insulate the barn's interior framing. Early on, I had leaned towards blown-in cellulose for its high recycled content, thermal performance and reasonable cost. However, I was concerned with it settling over time, unless I hired a contractor who could dense-pack it. But dense-packed cellulose in the deep roof trusses required a huge amount of material, which would be very heavy and very expensive. So I got more excited with the idea of spray-foam insulation, and eventually decided to go with Icynene for a variety of reasons- namely, its contribution toward energy-efficient sustainable design. Plus, I found a very sharp and eco-conscious local contractor who made me feel confident about hiring out the work. Never mind the high price tag- it is money well invested when it provides a healthy, energy-efficient home for the rest of our lives. So before the hired help arrived, I had to frame in a roof in the upper level of the silo. I made a 2X6 roof, covered it above with OSB and strapped it below with perpendicular 2X4 framing. This would allow for 9" of insulation with minimal thermal bridging. Plus, the access door and decking above would give me future access to the domed silo roof from the inside. The foam guys came the next day and sprayed the milkhouse roof, barn roof and silo roof (they'll have to come back to spray the walls once i've done all the electrical wiring). It was nice to see them so concerned with doing the job well, no matter how long it takes (and it took about 10 hours just to do the roofs!). Fiberglass should be outlawed...