Re: Closed Cell Insulation
I used open cell in mine. Couple reasons. 1) cost 2) I didn't want to "place a bag" over the top of my house and potentially trap in moisture. I figure it was probably meant to breathe a little originally as was the whole house. I didn't want to alter the envelope too significantly. 3) if there is a leak, I might get some notice. Although is reality, by the time water made it to the attic ceiling, a large section of wood sheathing would probably be too far gone already.
Another advantage of closed cell is that it actually provides some structural strength to the roof structure. It has the ability to provide some amount of bracing between the joists.
IN hindsight, I think I would have gone ahead and done closed cell. I do seem to get a fair amount of humidity migrating into the attic in summer. Although some of that might be air leaks that weren't sealed completely at the sill plate.
One lesson I learned is to remove all old insulation first... don't be cheap. The old insulation made it tricky to properly install the spray foam near the ends of the roof. OF course removing the old nasty loose fill junk would probably have cost almost 1/2 as much as I paid to have it spray foamed.
1925 Two-Story Stucco Beaux Arts Neoclassical