Superpower is defined as the ability to exert influence; powerful; great capability. Exterior walls, in their own right, serve a great purpose. At a minimum, they have one goal: to separate and protect the interior environment from the exterior environment. But there are many ways to build an exterior wall. Some design practices may warrant debate as to their resilience or effectiveness. However, one approach is widely agreed upon as the most practical and effective way to “superpower” the exterior wall: the rainscreen principle.

A rainscreen wall assembly can ultimately be viewed as a building envelope support system. This system acts as an overall system, as it groups components to provide a solution for water management, among other benefits. It performs the key responsibilities required of an exterior wall─keeping the interior space dry, warm, and physically protected─while also bringing a true sense of superpower to the exterior wall. Rainscreens are effective at aiding in the management of liquid water and water vapor, they provide exceptional opportunities for energy-efficient performance via continuous insulation and reductions in thermal bridging, and they can be tough enough to stand up to mother nature. At the center of all this, figuratively and literally, one key element of the rainscreen assembly arguably must do most of the work: the cladding support system. Selecting a rainscreen support system that bolsters this efficiency, durability, and performance is paramount.

This article explores the essential elements of a rainscreen, what the cladding support system must do in concert with other rainscreen elements, and important considerations to make during the design process, including building code changes and thermal efficiency.

Photo courtesy of Knight Wall Systems

Rainscreen cladding support solutions today can offer exceptional variety for ultimate performance. The system shown is a thermally improved and isolated steel clip and rail cladding support system with mineral wool insulation and zinc metal panels.

SHELTER IN THE STORM: PRESERVING DESIGNED PERFORMANCE WITH RAINSCREENS

A rainscreen, at a very basic level, is defined by the Rainscreen Association in North America (RAiNA) as an assembly applied to an exterior wall which consists of, at minimum, an outer layer, an inner layer, and a cavity between them sufficient for the passive removal of liquid water and water vapor. In other words, a rainscreen is an exterior wall where the cladding is offset from the back-up wall, creating an appropriately sized cavity for ventilation and drainage where liquid water can physically exit (drain) and/or evaporate (ventilation).

Assemblies that fall into this definition range from masonry, simple single skin metal panel assemblies, to clip and rail systems with face-fastened panels of fiber cement or high-pressure laminates. The 2024 edition of the International Building Code (IBC), available for review now, will for the first time officially codify this definition.

Photo courtesy of Knight Wall Systems

Thermally improved and isolated steel rail system with open-joint, face-fastened, large-format panels.

The Rainscreen in Operation

In general, a rainscreen’s operation allows any water that may pass by or through the cladding to easily drain away from the building, and the air that moves between the cladding and the wall accelerates evaporation of any residual moisture through passive ventilation.

Thus, the primary function of a rainscreen is not to provide barrier protection against water penetration, such as a water-resistant barrier does, but rather to limit the amount of water that could potentially come into contact with the building envelope’s water-resistant barrier.

Additionally, rainscreens have been proven to provide a solution for improving a building’s energy efficiency by providing the space for, and use of, exterior insulation. Thermally isolated rainscreen solutions provide a solution for attaching nearly any type of cladding to extremely efficient support systems, including offering an installation solution for true continuous insulation. This dramatically increases the energy efficiency of the building to meet, and often, exceed code requirements.

Elements of a Rainscreen

Rainscreen assemblies typically consist of multiple components, or elements. Each of these elements serve a specific purpose in supporting, and empowering, the exterior wall to carry out its duties. Not all elements described here are required to produce a rainscreen design, however in the modern era these elements are most commonly seen.

Photo courtesy of Ledgerwood Creative

Strong National Museum of Play, following completion of construction. Rainscreen installation of face-fastened panels.

Cladding, according to RAiNA, is defined as a "non-load bearing wall element, inclusive of any coating and/or finish, serving as the outer layer, which is unprotected from exterior environmental conditions.” Many examples of cladding exist, including brick veneer, metal panels, fiber cement, terra cotta, and others. Cladding is the outermost element of any exterior wall and with a rainscreen assembly, that is no different. Aside from good looks and stimulating visuals, the cladding has much work to do. It absolutely must withstand the harshness of mother nature and be tough enough to physically protect the interior environment – much like an exoskeleton.

It is the first line of defense against water, where upwards of 99% of the water can be shed away in typical designs. Fire protection is also an inherent and very important function of cladding; where flames may be adjacent to the cladding, its ability to ignite and propagate flame on a vertical surface become very important and not overlooked.

The cladding support system, otherwise known as the attachment system, furring system, subframing system, clip and rail system, grid system, or simply girts or rails, all serve the same general purpose. They must facilitate a way for the cladding to be attached to the back-up wall, or the structure. The desire to include this element in a rainscreen design is most often linked to the use of exterior insulation for boosting energy efficiency. This element, too, has much work to do. It resides in a moist environment, behind the cladding, and must have the capacity to withstand all the loads passed on from the cladding, which include the weight of the cladding itself, negative and positive wind pressure, seismic reactions from holding the cladding in place during an earthquake, and, potentially, even ice or snow loads (depending on cladding type and detailing). It must be resilient and durable so it may last many decades as servicing this component is inherently difficult given the concealed location behind the cladding. Resistance to fire must not be overlooked. Depending upon the chosen material, the components themselves could heavily contribute to the spread, or intensity, of a fire. In addition, the geometry of the air cavity created with the system will certainly have profound effects on fire performance.

While the air cavity is obviously not a physical element, it is arguably the most important part of the rainscreen assembly. It is where “the magic happens” and all superpowers come to life! Water that may pass through the cladding can be gulped up by the cavity and expelled through drainage and ventilation. However, larger is not better. In fact, studies indicate the increase in drainage and ventilation performance becomes insignificant once the cavity is over ¾ inch to 1 inch in size.

Exterior insulation will reside in the cavity created by the cladding support system, although the entire cavity must not be filled so the rainscreen superpowers can stay in full effect. It is important for the insulation to be capable of withstanding a moist environment. Many insulations exist for this specific purpose and include types such as rigid foam board, rigid mineral wool boards, and semi-rigid mineral wool.

Another element of a rainscreen assembly is the water control layer, which may be more commonly known as the Water Resistant Barrier (WRB), generally found on the surface of the back-up wall. This is the last line of defense against water making its way into the interior environment. Although, due to the powers at play from the rainscreen, this control layer should have minimal work to do. It is often said, and observed, that the water control layer only has to defend against roughly 0.1 percent of the water contacting the exterior wall. In modern design, the water control layer is often also the air control layer, which is beneficial for the performance of the building overall but also the rainscreen.