Some rainscreen systems are not necessarily designed to be 100 percent rainproof. Having a system offering open or partially-open joints on the building’s outer layer can be highly beneficial for ventilation and drainage of the wall cavity behind the facade and drying of the facade itself. As such, modern facades should be designed with three lines of defense in mind - the facade or veneer to deflect moisture - the airspace behind the facade to allow for drainage as well as for continuous ventilation - and a weather-resistant moisture barrier. Simply put, a properly detailed rainscreen system will greatly reduce the chances of water infiltration into the wall assembly and provide a continuous convection of air improving resistance to thermal transfer in the wall cavity.

Aluminum grid and clip veneer systems have found their way into the U.S. marketplace. This type of system allows masonry to compete in the curtain wall and rainscreen arenas with a stone unit that hangs from a substrate rather than bearing on the foundation wall.

The pre-engineered system consists of continuous horizontal channels which can be attached to a suitable substrate using screws specified for the system. The cladding material is then engaged into the channels on the wall. The best systems use continuous aluminum support channels or rails made from post-consumer scrap metals, augmented with thermally isolated components to improve the building’s thermal performance. Clips and anchors accommodate seismic and regular building movement. These mounting systems allow for a precise and far more technical way of mounting wall panels.

How to install a Gridworx Ultra System

The addition of thermal isolation components improves the performance of the building envelope by reducing thermal migration from the interior to the exterior. The encasement of fasteners, by way of sleeved washers coupled with thermal isolating back plates prevents thermal bridging in structural connections. These additions contribute to the building LEED certification as proven to be both “smart” and “green.”

For tall buildings subjected to higher wind loading, ventilated rainscreens require a greater level of engineering. Higher wind loads mean more pressure will be to the exterior cladding. This can cause greater stress to the cladding and the systems behind it. One solution is a pressure-equalized rainscreen, which relies on creating smaller compartments across a facade rather than one continuous ventilation cavity. These ventilation compartments respond independently to constantly changing wind pressure. When wind-driven air enters the wall the air pressure inside the cavity matches the wind’s pressure and “pushes back” against it, preventing wind-driven rain from entering. If a small amount of rain is driven into the cavity, the same openings allow the water to drain. Since these systems perform well under severe conditions, they can be shown to meet the approval of specific regional regulations, such as Miami-Dade County for hurricane resistance. This qualification should be considered a requirement in the selection of an exterior cladding system.

Old school full-bed masonry is experiencing a declining market share for a number of reasons. One of these is the economic efficiencies of thin stone cladding. Moreover, consumer demand has principally shifted toward the more contemporary look of stone.

In an attempt to address this demand, a number of new cladding products are now entering the market. Some of these include terra cotta, porcelain and sinterized stone known as UCS. All of these products are available in sheets of 5 x 10 feet or thereabouts. Rainscreen cladding systems are the perfect match for delivering these products to the market. For a variety of reasons our preferred choice is the UCS material.

What is Sinterized Stone?

Sinterized stone is a natural full-body pigment throughout the thickness of the material; it consists of 100% minerals. It is produced according to the innovative technologies on facilities that specialize in the production of natural stone.

Ultra Compact Surface (UCS) is sinterized stone that offers unrivaled durability. This material is crafted out of quartz, glass and porcelain; however, it undergoes a detailed, high-tech process that simulates hundreds of years of metamorphic change within the stones, resulting in a revolutionary product. Dekton and Neolith are examples of sinterized stone. Unlike natural porcelain, it provides a much denser surface and comes in thicknesses ranging from 8 mm, 12 mm, 20 mm, to 30 mm. It is graffiti proof UV resistant which makes it an ideal product for exterior use in an exterior application. These products can be fabricated in a variety of colors and textured to replicate stone or wood. These materials are extremely durable and color fast.

No matter how hot the surface gets, UCS will not crack, burn or scorch. This makes it a top choice for wall cladding and outdoor spaces. It is also resistant to extremely cold temperatures, so there is no need to worry about ice and thawing.

Attachment Methods

GRIDWORX is a company specializing in designing, engineering and fabrication of ventilated backdrop rainscreen stone cladding systems. They have developed several systems to hang UCS materials. This 12mm UCS panel is augmented with a saddle clip creating a faux Kerf for attachment to a continuous horizontal rail. Space is created between the substrate and the paneling that is perfect for insulation or access to other building systems with no interruption in the wall facade. Different panel makes and sizes can add accents like reveals and chair rails. With consistent channeling, wall panels can be suspended over open areas to create opens that seem to defy gravity. The channels can be used to mount kerfed panels horizontally for soffits and underhangs.

Another method of mechanical attachment is achieved with undercut anchors. These allow for attachment to the back of the stone similar to the well-known T31 attachments. They are designed for today’s thin and condensed materials such as UCS panels. Holes are cut with a special drill that expands when half way into the back of the panel.  When the compression screw is tightened it expands in the back of the hole (similar to a toggle bolt) securing it to the stone.

These anchors, combined with today’s contemporary cladding systems, allow ultra-sized panels to be set with dimensional adjustments creating technically accurate and well-defined joints.

Mounting systems are the unsung heroes of today’s wall cladding. The system creates safety, allowing the panel material to be the stars.

Designing to Withstand the Forces of Nature: Anchorage Systems

Anchors, which secure dimension stone to the building frame, are critical to the safety and durability of a building’s external cladding. The anchorage systems must be chosen or designed to meet the specific needs of each individual project; they are definitely not “one size fits all.” Therefore, each project must be engineered and designed based on the elements that affect the specific building.

From a structural standpoint, the stone panel is best thought of as a beam. That is, it receives a uniform load along its span, and it carries that load to the anchor points. These anchor points are engineered and found at an offset within the stone panel’s perimeter. When the panel resists the load, it experiences flexural stress within the panel itself. Design engineers responsible for this aspect of the project must make sure that the flexural stress of the stone panel does not exceed the allowable stress. This allowable stress load can be calculated using wind loads, density and measured flexural strength with the appropriate factor of safety for the specific project.

Three factors affect stone panels experiencing flexural stress: load, span and depth (stone thickness). First, heavier loads will result in increased stress within the stone panel. For example, a high negative wind load creates suction on a stone panel face during a storm. This increases the stress when compared to a low wind load situation.

The panel’s span between supports also affects the stress. Increasing the distance between the anchor points (i.e., the span) increases the bending stresses of the stone panel. In turn, this increase in area increases the total load: doubling the span quadruples the stress, giving it a “squared” relationship. Finally, the thickness of the stone is comparable to the depth of a beam. It also has a squared relationship to stress.

This is presented to make the reader aware of the necessity of having the project engineered by a registered Professional Engineer registered in the project state.

Conclusion

Today’s cladding technology provides architects with a notable alternative for creating facades on new and existing buildings of all types. As a durable product manufactured from all natural materials, UCS has proven characteristics and capabilities. The variety of colors, textures, and appearances can be used for a wide variety of design schemes and intents. The inherent sustainability of the product makes it quite suitable for green building design. Overall, it is a high-quality product that can be readily and economically incorporated into building facades.

A building envelope has several critical jobs to perform, including keeping the rain out while controlling air leakage, vapor diffusion and heat transfer. It should also look good while doing it.

Architects, builders and installers are well advised to consult with a qualified and experienced cladding design firm before embarking on any ventilated backdrop rainscreen system. For additional information on the contents of this article, please visit www.gridworxwalls.com.