Insulation behing battens on IWI

Hi All,

I am going to put IWI in my Kitchen. I have two questions. I intend using 38 x 63 CLS as I already have some left over from another project. I don't have much floor space in the kitchen, I can only get 6 units in it, and so can't afford to lose much space.

My first question is will it help if I put 12mm Celotex against the existing external wall surface and then mount the CLS on the top of that? I intend using 50mm Celotex in between the battens. Will I need to run the vapour layer behind the battens ie a continuous vapour barrier (will aluminium tape do?) covering all the Celotex going in to cover the 12mm and coming out along the side of the 50mm till it reaches the foil facing?

As I can hear a pin drop in next door, and the mother shouting at her son, I intend putting some sound insulation (Earthwool Acoustic Roll from Knauf Insulation) along the party wall. What should I do at the corner where the IWI will join the Party Wall insulation? I guess it will have to be a compromise between sound or heat insulation unless I can cut them at 45 degrees.

Simon