Layers on uneven wall?

[Philxyz]

Hello

We have a small cottage in Ireland with exterior walls of old stone and 100mm EWI. This is the plan:

• 100mm EWI (exists)
• 400mm old stone wall (exists)
• Breathable airtight membrane against wall
• 20mm air gap
• Thermally bridged metal stud frame (with insulation)
• Plasterboard

 

Does that look like a good plan?

 

Do we need a vapour barrier?

The old stone wall is sometimes exposed repointed stone, othertimes several renders. It is extremely uneven. How do we secure the stud tracks to a wall that is all over the place? Any ideas for this appreciated. I imagine an adjustable bracket hopefully providing a thermal bridge but cannot find anything.

 

Many thanks, Phil