How do I finish where wall meets roof?

[diy lou]

The walls in my house are stone/rubble walls and in this room at some point it appears a concrete render has been put on the inside.
We had a major ongoing leak in this room that was finally discovered to be coming down a chimney we didn't know existed (there are apparently two in the room, one going to the fireplace and another going to where the existing window is). We have now had the chimney removed and the roof tiled over and no longer any damp issues (hurray!) - though it will obviously take some time to dry out.
On trying to locate the source of the problem we removed sheets of kingspan that had been screwed to the wall above the beam, the wall was dripping wet behind probably from the damp not being able to evaporate but possibly also from condensation.
My question is, how should we now finish this end wall above the beam where the kingspan once was - as you can see at the top there is the glass fibre yellow insulation in areas so I am not quite sure how we would cover this - I wouldn't have thought replacing the kingspan would be an option due to the potential condensation issues - any thoughts gratefully recieved! Thanks.

 

[Scarlet Pimpernel]

A few options perhaps,
1. Re-use the insulation but add a vapour barrier to prevent vapour reaching the wall and condensing.

2. Remove all insulation and use a lime render/plaster. You'd probably have to remove the existing cement render first.

3. Ensure that area is heated and well ventilated.

It would probably help to use a dehumidifier to reduce the vapour in the air. Ensure the room is heated and sufficient circulation of air is maintained.​