The largest portion of the exterior is clad in fiber cement.
We are using a 12″ lap siding by CertainTeed but using it in a slightly unconventional manner.
We are planning to run the lap boards vertically as opposed to the traditional horizontal manner. Further, the joints will not be lapped but will be open with a very small reveal between each of the boards.
The complete system is designed in the fashion of a vented rainscreen. Essentially what this means is there is a small gap between the exterior siding material and the sheathing behind. This gaps serves a couple functions but the key function is the ability for water to move through this opening. In a traditional siding application, the material is fastened directly to the sheathing, with no gap. If water reaches this point, it has no where to go and simply sits on the surface. While there is a weather barrier in place, you can still imagine that this is not good for the system. In a rainscreen application, the water has a way out. It no longer sits on the surface, but is allowed to move down the length of the wall and out the base. The rainscreen increases the life of both the exterior cladding and its subsurface.
To achieve this small gap, we are running furring strips a 12″ on center at each joint of the vertical fiber cement boards. We are using a metal product called Furring Master. These are 22 gauge galvanized steel which ensures they will not warp or degrade over time. Further, they are designed with an almost u-shaped profile, creating a hollow channel, allowing for water to escape in the rare event that it would actually get behind the furring strip itself.
Again, thanks to the folks at Postgreen for all the great posts details much of the process they went through. While I have been familiar with rainscreen systems for some time, they have used the Furring Master product in the past with great results. Here is an image of their Skinny Project with the furring strips installed: