I was looking round a friend's house over the weekend as he is trying
to decide how best to insulate a bedroom ceiling. He has a dormer /
bedroom built into the loft (before he moved in) and at one end of the
room in an area about 6m x 2.5m, this has a good ceiling but it is
under the roof and peering up into the space through a removed light
fitting, it looks like was very little insulation put in that space
when it was built.

To add insulation now is virtually impossible without either removing
roof tiles, taking down the ceiling or, perhaps, blowing insulation in
the space as is done for cavity wall insualtion installation.

The best option seems to be to work from inside the room and add
insulation below the ceiling itself. The ceiling itself is in very good
condition - plasterboard which has been emulsioned. First thoughts are
either:

1. Put up ceiling tiles directly onto the existing ceiling.
Questions:
What would be the best ones to use from an insulation point of view and
where to get them?
What adhesive to use to get a good bond to the emulsioned plasterboard?

2. Put up insulation on the ceiling and then tile over this. The
advantage might be that additional thickness of insulation could be
built up first and then the tiles added.
Questions:
What would be the best insulation to use? I have seen 50mm polystyrene
panels in Wicks BUT, before anyone mentions the fire risk, I do know
about that and was just using these as an example. Wouldn't dream of
using that stuff!
Is there a fireproof / resistant alternative to this kind of insulation
suitable for the job? It would need to have a smooth finish on both
sides.
What adhesive to use to get a good bond to the emulsioned plasterboard
and then what adhesive to use to fix the tiles to this?

There is plenty of height space to add insulation and then tiles.
Obviously, while going to the trouble of doing the job it needs to be
done properly and provide the best insulation possible.

If anyone has any ideas, suggestions or comments, they would be
gratefully received.

Many thanks,

Peter