We have our thermohouse panels installed for the flat roof:

 

 

Here is their basic detail for a typical flat roof, but doesn't show how the void is ventilated:

 

 

I spoke to them and they recommend soffit ventilation to stop the batons/firring strips from rotting. We want a minimal detail with render right up to the 90mm drip flashing, so I'm not sure how to achieve this... if it's even needed?

 

 

I think this is EXACTLY what we need:

 

https://www.turboslug.com/selfbuild/modernist-self-build-insulated-render/

 

Just need to figure out how to build out the render board and leave a vent gap up to the underside of the deck.... ideas welcomed!!