Currently I just have the joists there. I need to insulate it, and cover it up, so what I was planning to do was: - Screw some kingspan to the underside of the joists, to ensure the joists don't act as a cold bridge. - Screw some ply under the kingspan to cover it. - Add some additional insulation between the joists, above the kingspan.
In fact I have a bunch of plasterboard backed kingspan offcuts that I might use here, so would attach it plasterboard side up (so plasterboard side faces upwards).
Does this sound like a sensible approach?