These concerns have always been important, but in view of a weak economy and heightened awareness of the environment, building smart is more relevant than ever. A key element in protecting your investment and improving building health, safety, welfare and sustainability is the addition of an effective moisture management system in the building envelope. Adding more insulation and better windows and doors has greatly improved the thermal abilities of walls. It has also had an impact on the building envelope’s ability to shed moisture.
Moisture can enter the building envelope in a variety of ways including wind-driven rain, leaks in the veneer material, condensation, and poor maintenance and detailing. Few experts will argue the fact that eventually, the building envelope will experience entrapped moisture. There has always been moisture intrusion into the building envelope; the reason it wasn’t a major problem thirty to forty years ago is that buildings weren’t as tight, and air could get in and dry the walls out. Modern structures don’t allow this free movement of air in the building envelope—hence the huge increase in rotting building materials, toxic mold, and other moisture-related issues that have exploded over the last couple of decades.
Fortunately, there is a solution–the rain screen drainage plane! The National Association of Home Builders 2008 Report stated, “Construction professionals involved with developing construction practices for ‘absorptive’ or ‘reservoir’ type claddings are increasingly recommending the supplementation of the manufacturer’s existing drainage and drying features by the incorporation of additional positive drainage and drying features, regardless of the cladding manufacturer or particular manufacturer’s guidelines… One approach for achieving such an enclosure is through the use of a ‘rain screen’ design approach.”
Moving from the outside in, a rain screen wall consists of a veneer of some type (masonry materials such as stucco, brick, and stone and also cladded sidings), then a permanent predictable void, followed by a building wrap, then sheathing and finally wall studs. This type of building envelope anticipates that some water will get through the veneer. However, if there is a predictable void behind the veneer, that water can be channeled downward and out of the wall before it can move into the building wrap, sheathing and studs where it can take up residence and produce the health and sustainability problems that destroy buildings and create health problems in residents.
Today, most architects and contractors agree that measures need to be taken to prevent moisture entrapment; they also agree that rain screen walls can be an effective tool in the quest for improved occupant health, safety, welfare and building sustainability. What they don’t agree on is how to maintain this predictable void/drainage plane area behind the veneer in a rain screen building envelope. There are many products available that claim they will drain the wall; however, many are ineffective or at best, minimally effective. Over the next few months, we will be discussing what works and what doesn’t. These discussions will be based on scientific testing, not conjecture. We invite your views and look forward to improving the way building envelopes are constructed.