This page contains a Flash digital edition of a book.
A Unifi ed System Exterior wall systems progress to integrated rainscreen design


The rainscreen principle, time-tested throughout Europe for two centuries, pro- duces healthier, more energy-effi cient and longer lasting walls. Furthermore, it liberates aesthetic considerations of a façade from the im- portant functions of a weather barrier wall. However, the typical rainscreen system retains


certain shortcomings, which are now eliminated by integrated rainscreen design. Before consider- ing this innovation, we fi rst should examine typical face-sealed wall design concepts used extensively in the United States.


Problems Associated with Face-sealed Wall Design With face-sealed wall construction, the outermost cladding material attempts to serve multiple func- tions, including aesthetics, air barrier, water barrier and/or wind barrier. These types of designs are prob- lematic for a number of reasons, primarily because they are functionally overburdened and denied the benefi t of the “belt and suspenders” approach of- fered by an integrated rainscreen system. To begin with, traditional face-sealed design


relies on the air and water tightness of hundreds of panel-to-panel joints and other panel transitions including jamb, head and sill conditions, and inter- faces between various cladding materials. In many face-sealed wall systems, caulking is commonly used to create these seals, requiring perfect installation. In addition, no caulking is permanent. It degrades over time, usually as soon as fi ve to 10 years. Caulking can stain, collect dirt and is costly to maintain. When joints or other interfaces fail, large


amounts of moisture will penetrate the wall. Mois- ture-laden air is drawn into any breach in the joint because of air pressure differences inside the wall versus outside the wall. When liquid water is pres- ent in the wall cavity, traditional weather barrier wall design has no method of effectively draining


or drying it. The infi ltrating water damages insula- tion (rendering it much less effective), corrodes any metal components and creates a desirable condition for mold propagation.


Typical Rainscreen Wall Construction Rainscreen design acknowledges that face sealing exterior walls is an exercise in futility. With a rain- screen assembly, the burden of weather/climate management moves from the outer wall to the inner wall. The outer cladding’s only role, beyond aesthetics and long-term durability, is to serve as the initial defense against rain and, in some applica- tions, to handle heavier wind load. The inner wall now does the heavy lifting: it


serves as a drainage plane/water barrier, air barrier and thermal barrier. The open cavity is essential to promote air fl ow


via the chimney effect to rapidly dry out the cavity. The preferred practice is for an integrated ventilation system to be engineered into the wall assembly. The air and thermal barriers are continuous and


outboard of the framing studs to eliminate gaps and minimize thermal bridging via the fl oor slab or steel framing elements. Even with a well-designed high-performance


rainscreen system, certain obstacles still exist to delivering the system as intended. These include product substitutions that not only compromise the purpose of the design and fail to consider an indi- vidual component’s role as part of a unifi ed system, but create a climate of ambiguity regarding who (which supplier or installer) is ultimately responsible for system performance.


Integrated Rainscreen Wall Design Problems can be managed when they are antici- pated. An integrated rainscreen system, such as the IntelliClad Complete Rainscreen System from IMETCO, Norcross, Ga., is designed with the under-


By Amy Stokes


standing that preventing all vapor and water penetra- tion is nearly impossible. By anticipating that some water and vapor will penetrate the exterior cladding, a properly designed integrated system can manage it quickly and effectively within the cavity. A properly designed integrated rainscreen


leaps over both traditional face-sealed walls (reli- ant on imperfect joints and seals) and air barrier systems that are vapor impermeable (providing no exit strategy for when, inevitably, vapor penetrates inside) by making sure that all components work together to create a unifi ed system. If we use the IMETCO system as an example,


an integrated rainscreen assembly includes: • A variety of exterior cladding options, each concentrated on three priorities—shedding rain, material durability and design latitude.


• A 1-inch air cavity, created in this case by perforated hat channels that eliminate the need for vertical subgirts, and require minimal fasteners to attach to the studs resulting in negligible thermal bridging.


• High-density continuous insulation board (the IMETCO system uses a stone wool product that is unaffected by water and provides outstanding thermal insulation).


• A continuous vapor-permeable air barrier system with an effective transitional interface between the walls and the roof to maintain its continuity. An integrated rainscreen system is a


sustainable solution suitable for any building application, especially when an owner is concerned with life cycle costs and long-term, reliable energy effi ciency.


Amy Stokes is the marketing manager at IMETCO, Norcross, Ga. For more information about IMETCO and its IntelliClad Complete Rainscreen System, visit imetco.com/IntelliClad.php.


Traditional face-sealed wall design is functionally overbur- dened, relying on "perfect" installation of hundreds of panel joints and transitions, as well as degrading caulking and sealants that require costly maintenance every few years.


With typical rainscreen design, the cladding serves as the initial line of defense, while the inner consists of a drainage plane, air barrier and thermal barrier.


An integrated rainscreen, such as IntelliClad, comprises environmental control layers that address rain, air, heat, and vapor in an all-in-one complete rainscreen assembly.


www.metalconstructionnews.com


December 2012


METAL CONSTRUCTION NEWS 41


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68