One of the most reliable ways of both keeping our walls dry, and allowing them to dry out if they do get wet, is to construct the wall with an outer shell that we call a rain screen.
Rather than trying to make the siding on the house absolutely waterproof, which never works for a very long time, we design it so that it sheds most of the rain that hits it, drains what gets inside and ventilates the siding to dry out the wall.
Just how do we build rain screens? This animation developed together with the National Research Council of Canada will give you a good visual introduction to the basic concepts.
For more construction details follow this link.