75mm timber stud wall insulation thickness

[elbow]

I am constructing 75mm timber stud walls and need some advice on the required quilt insulation thickness. The architect has detailed 75mm insulation, i.e the whole void filled whereas my plasterer reckons it should have a air gap so to use 50mm insulation.
Who is right?

Cheers

[stoneyboy]

elbow,
Void should be fully filled.
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