I am about to start dividing off my extended garage to create a man cave. This involves a studded dividing wall which along with the other three outer walls need insulating. Incidentally the garage is a timber framed structure with CLS roughly 4x2 frames with 18mm shiplap over a breathable membrane and lined behind with plywood. The plan is to fill up the spaces in the framework with either Celotex or Kingspan foam panels.

So the question is, can the foil coating do as a vapour barrier using sealing tape across the framework as I did when insulating the kitchen floor or do I need to add a polythene sheet over before boarding the inner wall?

I have been watching some YouTube of people doing similar things and have been left confused. The following video is a compilation of a number of videos of a professional build of a garden room.

https://youtu.be/S92rEaAj188

The guy insulates the bays between frames with foil coated foam panels before adding a rock wool bat sound deadening layer and then a vapour barrier before plaster boarding but then cuts holes in the PB for sockets destroying the vapour barrier behind?

Got to admit some of the work looks rough and some to my mind over engineered. See what you think the relative insulation is towards the end of the video or you can look at the daily video record of 15 daily videos.

Richard