timber frame build

[Thegroundhog]

looking for opinions on the following timber frame build

out to in
sand and cement Monocouche Render
12.5 mm fibre cement board
50 x 38 mm treated batton
50 x 38 mm treated counter battons
Tyveck fixed to 11mm OSB 3 board
140 mm rigid insulation board ( quinn, kingspan etc)
vapour barrier
28 mm slap
skimmed

 

[^woody^]

What are the counter battens for?

 

[Wendelspanswick]

What is your target U value, I am looking at doing something similar and the cheapest way seems to be 140mm of Knauf Earthwool which gives me a U value of 23.