I’ve been involved is a lot of construction and can’t figure out why there is room enough for a man between the inner and outer walls???????Most plumbing, wiring etc is between inside walls to protect from weather.
I believe it’s an insulating feature - like a type of air buffer, that provides for some additional insulation for the building - I’ve also heard it’s a fire safety feature and helps keep some types of fire from spreading too quickly. But then again, I’m no engineer.