Warm Flat Roof Edge Detail and Preventing Heat Loss

[Julia123]

We've just had some roof insulation installed on top of the old felt flat roof above our living room, however it is very draughty in the void between the joists as we found when we popped out one of the ceiling lights, and so the heat is still escaping.

From top to bottom the roof make up is:
New felt
Insulation board
Old felt
Old ply
Joists and firrings
Plasterboard

The fascia is screwed to the end of the joists and this is the only barrier to stop the heat in the ceiling void escaping sideways, as the joists sit on top of the brick outer wall. What should be the detail here? I understand a warm roof design doesn't need to be vented. Thanks for your help.