I think the right term is ventilated air space. It is basically a double wall with metal strips between which make a gap between the two sheets of cement board. The second sheet is placed a bit higher which allows cold air to come in from below, heat up, and exit from the top - making a circulation of air. This should lower the temp of the wall if I am not mistaken. No need to go all the way to ceiling... and I like the way this looks.