Here is a cross section of how I understand the structure / insulation:
11mm OSB 3 fitted to the inside of the timber frame.
50mm Rockwool / Celotex or Kingspan fitted up against the back of the OSB.
20mm Air Gap (Due to 70mm wide timber frame)
Breathable Membrane stapled to the outside of the timber frame
Battens screwed / nailed through the membrane into the timber frame
Cladding fitted to the battens (Either wood or plastic TBC).