Insulation help for flat roof

[spottedwales]

Recently purchased a 200 year old house. in one room the ceiling plasterboard has been entirely removed, and it looks like there was a rockwool type insulation installed before which has also now gone. Its now basically ceiling joists and then the flat roof, there is a membrane obviousley and no signs of any moisture entering through the roof. I need to know what type of insulation I should fit in between each joist before putting new plasterboard up. I hve one person telling me I can use the rockwool sheets, but another telling me it should be something like Kingspan or Celotex. Any advice to a very new DIYer is welcome

 

[ree]

OP,
Why not post pics of the ceiling joists - the outside at eaves level - & the surface of the flat roof?

 

[noseall]

Recently purchased a 200 year old house. in one room the ceiling plasterboard has been entirely removed, and it looks like there was a rockwool type insulation installed before which has also now gone. Its now basically ceiling joists and then the flat roof, there is a membrane obviousley and no signs of any moisture entering through the roof. I need to know what type of insulation I should fit in between each joist before putting new plasterboard up. I hve one person telling me I can use the rockwool sheets, but another telling me it should be something like Kingspan or Celotex. Any advice to a very new DIYer is welcome

Are there any vents, currently venting the space between joists, to the outside?

 

[Tigercubrider]

Following

 

[spottedwales]

I dint think so but the room is freezing lol so maybe, not sure what to look for to be honest

 

[^woody^]

If it's a flat roof, you should be seeing some sort of wood, not a membrane.

 

[spottedwales]

Some pics, the roof is flat above here

 

[Deluks]

Not technically a flat roof then.
Is it a sloping roof with the top part flat?