Stud lining single external walls - to leave a void or not?

[AFT4B]

We are converting the garage as part of our extension/ house renovation. One of the walls adjoins the neighbour’s garage is a single skin wall and the front (where the garage door was) has also be rebuild in single skin.

The specification from the architect is as follows:

UPGRADING EXISTING SINGLE SKIN PARTY WALL (cold adjoining space)
To achieve minimum U Value of 0.30 W/m²K
The existing walls must be checked for stability and be free from defects, as required by Building Control.
Provide a scratch coat render to existing wall. Construct a studwork lining using 100mm x 50mm treated
timbers with head and sole plates and noggins at 400mm centres. 100mm Rockwool flexi to be provided
between studs and provide 45mm Knauf thermal laminate plasterboard with VCL over studs.
Finish with 3mm skim coat of finishing plaster. All junctions to have water tight construction, seal all
perimeter joints with tape internally and with silicon sealant externally.
The party wall to achieve a minimum 60 minutes fire resistance (REI 60).

There is no mention of leaving a void between the masonry and studwork. Nor a mention of there being any sort of membrane on the masonry side of the studwork. Would this be advisable if I want to go belt and braces or is there a technical reason not to do this?

Also, why a scratch coat render instead of the wall being tanked?

 

[Wayners]

I just screwed timber to wall and pushed in 50mm kimgspan between timbers.
Then screwed foil backed plasterboard over.
The kimgspan acts as a moisture barrier.
The foil on the plasterboard also blocks moisture.

Charliediy on YouTube has multiple videos with the different systems he has tried over the years. He was happy with the last one he did saying it was the best system in march 2025.

As for your question.

You don't need air flow with your system. You don't have a damp problem. It all dry.
I seen some use breathable membrane but I don't know what its for on some walls.

I think your system is so the moisture can go through and out not trapping it