Foundation and Wall Design - Air Gap Or Not
Some people advocate an air gap in the wall, but not me.
It is common practice to include a 1 inch air gap between brick veneer on the outside of a house and whatever material is the start of the inner wall. What's more it's a prescriptive building code requirement and there are good reasons why having a gap is a good idea. A gap allows the outer brick to be an independent rain screen. Rain hits the brick and completely saturates the brick with water. The water runs down the outside face, the inside face, and even through the middle of the bricks without coming into contact with the inner wall.
If it's a good idea, why haven't you done it?
You will notice in the diagram that there is no air gap between the outer stucco and the inner wall. My reasoning is that it is unnecessary given the proper water vapor design of the wall. If the wall was a stick built frame type covered in house wrap, I would absolutely want an air gap. In my design however it does not matter if the rain gets through to the EPS sheet. Water will not harm the EPS sheet and it will dry out when the rain stops. The EPS distributed vapor barrier will ensure that the rain water cannot get as far as the concrete and the actual inner wall. Also the stucco is fairly water repellant, so the outer surface is a drainage plane, so a drainage plain on the inside surface or an air gap is not necessary.
Implementing an air gap would be a pain to do
I am not fundamentally against the idea of an air gap, but given that it is unnecessary with my particular wall design, it would be unnecessary work and material cost. To give the stucco a sub-straight to be applied to it would be necessary to use some sort of backing boarding such as Hardie Cement board. That would be applied over wooden batons. Given that it will be a wet zone, the wooden batons will need to be pressure treated wood to try to slow up them rotting. The cement board will probably flex a bit which would cause the stucco to crack. As I said, I am really not keen to implement an air gap.