Help deciding on wall material for my shed project

[givingitagoimnotapro]

Hello,

I’m in the middle of converting the old coal shed in my garden to an office. Originally it was letting water in from the concrete roof, the walls and from the old door. I’ve since installed a double glazed door and took advice from a friend to DPM the whole room and roof externally and then im going to get my friend in to eventually K-rend the external wall.

Since doing all this work it seems water tight. The only issue is condensation on the walls and roof due to it being so water tight but with no heat at the minute to balance it out. I want to put 25mm insulation board and then 12.5mm plasterboard on the walls using foam adhesive - so, this is my question as ive been looking at the boards with insulation on the back, they seem to be paper backed and not foil backed, so im concerned thats the paper back would soak up moisture which would then in future cause mould. Would you use the 25mm foil backed celotex and then install foil backed plasterboard or moisture board to help minimise this? Their will be a heater put in the room once its all boarded and skimmed. Ive added some pictures for reference to the room - I’m up for heavy criticism if ive done it incorrectly

 

[Wayners]

Not really my area of knowledge.
I'd just stick foil backed insulation on with foam.
Then stick plasterboard on that with foam and polymer grab mastic.
Could add a few of those plastic hammer in fixings through but not sure id bother.
The foil back is a vapour barrier.
Looks like you've tanked room?
Id surface mount cables. They are a problem if under insulation I understand?
Jmo

Oh . You will probably need a dehumidifier and run a few hours a day in the winter