One moisture transport mechanism that is often overlooked in building construction is capillarity or capillary suction. Capillary suction acts primarily to move moisture into porous materials. For example, a paper towel, with one end in contact with liquid water, draws water into itself against the force of gravity as a result of capillary suction.
It is pretty weird to dig a big hole and drop a building into it. A one story house with a basement is really a two story house that you dropped into the ground burying one story. Think about it…now you have to make the part in the ground strong enough to keep the dirt out. Even more difficult you have to keep the water out. Oh yeah, you also have to keep the soil gas out. It is kind of dumb to try to install windows. What are you going to look at? Worms? So you surround the windows with vertical shafts in an attempt to connect them to dayligh
The basis of the current ongoing Canadian Civil War between pressure equalization and ventilated and drained claddings (open-joint cladding systems). Old school engineers like me were taught by Old Masters like Handegord who pointed out that drainage was the key to life in general and pressure equalization—if it applied at all—was for joints and not for entire wall assemblies. Claddings were to be drained. Ventilated if you must, but first and foremost they had to be drained.
Air barriers have always been a big deal in flat roofs in cold miserable places like Canada even with black roofs. But back in the day you could get away without an air barrier in a flat roof in Washington, DC if the roof was black. Winters were not long enough or cold enough to cause problems and any moisture that did migrate upwards was driven downwards due to the extreme temperatures the black membranes would get to–above 180 degrees F.
The perfect wall is an environmental separator—it has to keep the outside out and the inside in. In order to do this the wall assembly has to control rain, air, vapor and heat. In the old days we had one material to do this: rocks. We would pile a bunch or rocks up and have the rocks do it all. But over time rocks lost their appeal. They were heavy and fell down a lot. Heavy means expensive and falling down is annoying. So construction evolved. Today walls need four principal control layers—especially if we don’t build out of rocks. They are presented in order of importance: