“Rainscreen, eliminating the pressure, not the opening.”
In order for water to penetrate a wall, three components must be present:
Since eliminating the opening is not realistic, the Rainscreen system focuses on eliminating the pressure difference. Since eliminating the opening was rendered an imperfect solution to the problem, efforts turned to the elimination of the third component, the force that drives water through an opening. The forces most difficult to combat in this capacity are air currents and pressure differentials. “Air currents result from differences in wind pressure over the wall surface, or from convection within wall cavities, and these may carry water into the wall. Also, when water is present on one side of an opening, and the air pressure on that side is greater than that on the other side, the water will be moved through the opening, no matter how small, in the direction of the pressure drop.”
The first component, water, will always be present. The traditional construction wall efforts focused on trying to eliminate the second component, the opening, by caulking the joints in the wall in order to diminish any openings for water to penetrate. This is an ineffective solution for many reasons, including:
Caulking material needs to resist both rain and air (pressure differentials), which requires absolutely no rain leakage paths. Because of this, caulking needs to be perfectly applied in order to be effective, and perfection is impossible to achieve.
Caulking material is directly exposed to the elements, where the weather causes the material to expand and contract, and finally crack; therefore the caulking needs to be consistently maintained, and this maintenance is costly.
Caulking material deteriorates and fails when exposed to UV rays.