If you’re like me, you’ve been working on understanding the exact deﬁ nition of a “rainscreen” and wonder why it hasn’t been more fully embraced as a common system in this market. I was ﬁrst introduced to the rainscreen principle when I was in graduate school about twelve years ago and the ﬁrst ﬁrm I worked for employed the philosphy in just about every building that was designed.
I thought I had a pretty good handle on it until I came across an article published by the Metal Construction Association entitled, “Understanding ‘The Rainscreen Principle.’ It says, of TWO different kinds of rainscreen designs,
“Both systems emply open joinery and allow a certain amount of water into the cavity area between the outer and inner leafs. Drained/Back-ventilated systems rely on the ventilation cavity to both drain and dry-out residual water. Pressure-equalized systems (PERS) employ drainable compartmentalization to limit water penetration during periods of pressure disequilibrium and to facilitate rapid pressure equalization.”
Unlike a conventional wall design which assumes a “single line barrier,” relying on sealant integrity, both rainscreen systems plan for the inevitable intrusion of water into the wall assembly and provide a pathway for that water to escape before building up and ﬁnding its way through the entire assembly. Not a bad plan for buildings that are seeing a rapid change in the name of energy efﬁciency and tighter buildings and the resulting periods of “pressure disquilibrium.”