calculating blown in insulation
One point to keep in minid is that without an air barrier, the effective thickness of batten insulation is greatly reduced. You can have R-40 worth, but on about R-25 to 30 will actually be performing. This is due to air currents on the exposed side of the insulation. Figure into the project adding a layer of tyvek on the attic side of the blown-in. If you put it in and staple it before you blow then you can just fill it up. It would be easier to install it before rather than after.