Insulating vaulted ceiling

[rix313]

I've taken out an airing cupboard in a bedroom to make some space. The gap between the roof slats and the cieling is quite big. It looks like the beams used to be on show and the ceiling was dropped. Currently there is the roof, fibre insulation, the old plaster board ceiling panels, foam sheets then the current ceiling. What am I best insulating the empty section with? Also what method is required to hold the new insulation in place? Contact adhesive etc?

 

[foxhole]

Celotex insulation boards, leave a 50mm air gap on top, cut to fit tight and they hold without adhesive.

 

[chappers]

seems a bit pointless using celotex unless you've got some for free if the rest of the roof just has rockwool.