Today two main ways exist for a wall to be built to address rainwater: a barrier wall or a rainscreen wall. Most walls built on homes, townhomes, or condos today are rainscreen walls. A rainscreen wall is, for purposes of water control, essentially a double wall. The exterior surface of the wall sheds rain water down the building. However, that exterior surface is not completely watertight, and it is expected that some water will get behind the exterior material. Water that gets behind the exterior material meets a second barrier: the weather barrier. The weather barrier is a continuous layer of material that will not permit any water to pass through and which uses gravity to drain the water down and out of the wall system.
The alternative to a rainscreen wall, a barrier wall, is what its name sounds like: the exterior surface of the wall intended to serve as a complete barrier to the entry of water. In a barrier wall, no water should get behind the exterior surface of the wall. The problem with barrier walls is that they are very hard to construct. Many materials are porous to some degree, cracks will form in materials, and intersections between materials will not be perfectly sealed. Because they are so likely to fail and let water into the wall system, barrier walls are less commonly used compared to rainscreen walls.
While rainscreen walls generally are better in humid, windy climates like South Carolina and the Southeast, rainscreen walls can also have problems. For example, if the weather barrier is not properly lapped or not continuous across the face of the wall, water can get behind the weather barrier and rot the structure of the building. If flashing installed at the intersection of different components in a rainscreen wall is not installed properly, water can get behind the weather barrier and rot the structure of the building. In other words, rainscreen walls provide two layers of protection, rather than the single layer of protection in barrier walls, but rainscreen walls still often fail resulting in damage to a home’s framing and other components.