It seems counter-intuitive to add holes to a wall to keep the building envelope dry, but it is a necessity in rainscreen building envelopes. In preparing for a presentation we will be doing at the Sealant, Waterproofing & Restoration Institute 2010 Fall Technical Meeting this October, I came across an excellent article by Brett Newkirk entitled, “Creating Holes to Stop Leaks” in the August issue of The Construction Specifier. If you have any reservations about the necessity of drainage in rainscreen walls, I encourage you to read this article.
In summary, Newkirk posits, “Holes or weeps are needed in buildings constructed using water-managed cladding systems…because it is anticipated that water will penetrate the veneer and drain down the underlayment and exit to the exterior.” We need to provide a drainage plane and weeps (holes) at the lowest point in the wall to make this possible! According to Newkirk, “The only type of wall not requiring holes is a ‘barrier’ system…and that is an extremely difficult system to successfully achieve 100% of the time.”
So what’s the quick take? In MTI’s opinion, and it is an opinion based on testing and research, if you are building with a rainscreen building envelope, you need to provide a drainage plane and weeps (holes). The drainage plane needs to be a predictable void behind the veneer; it also needs to be a predictable pressure equalization plane. The weeps are an integral part of this drainage plane system, and they need to be placed frequently and at the lowest point of the wall.
Newkirk goes into great detail about the why and where of “holes”. The article is available online, and I encourage you to read it. Those are my thoughts, as always, I welcome yours!