I plan to redevelop a porch into a toilet, where the porch is located under the original roof (i.e. it has an existing recessed front door). As a result, I will create a new external front wall, and plan to remove the external brick skin of the existing porch to maximise toilet dimensions (all structure is supported on the internal skin).
Above ceiling height, as the then single skin internal wall will be in the roof void, I wish to add insulation to the wall. I am considering using something like 200mm of Celotex or equivalent.
My question is, how would one attach the Celotex to the single skin wall, and to what extent is vapour sealing required (membranes?).
Is there anything else I should be aware of?
Thanks in anticipation Paul R