Fiber Cement Ventilated Rainscreen Cladding Systems

Cladding System Criteria

Exterior wall cladding systems form the exposed “skin” or the exterior finish of a building. They are the visible, aesthetic face of a building but are dependent on everything behind that face. That includes the design of the system that supports the cladding and coordination with the rest of the building construction. Additionally, there are several performance requirements that must be met based on building codes and standards. The first is that the exterior cladding must shed bulk water and resist weather conditions. Note that it is not required to seal water out completely, but to shed it or allow it to drain away behind the cladding. Such systems are often referred to as ventilated rainscreen cladding systems. The International Building Code (IBC), which is the norm for most of the United States, establishes minimum basic levels of performance for all such cladding systems in terms of flexural strength, material integrity, resistance to damage, etc. In certain areas where extreme weather conditions are more common, such as Miami/ Dade County in Florida and other coastal areas of the country, a higher level of requirements are mandated and enforced locally. This includes enduring heavy rains, high winds, and puncture resistance to objects blown around by those winds.

Beyond the cladding layer, the IBC mandates the use of an air and water barrier (AWB) placed over the sheathing layer of a wall system to prevent the unwanted intrusion of water or air infiltration. This layer acts as the true weather barrier for the wall and ideally allows water that penetrates the cladding to drain down harmlessly along its surface. There is also the energy code requirement for providing thermal insulation in an exterior wall system, with continuous insulation preferred (due to its greater effectiveness) between the cladding and the wall structural system. The insulation needs to be capable of good performance and resiliency in the event it becomes wet.

Of course, all exterior wall cladding systems need to be held in place with a structural sub-structure that attaches to the main building structure, such as concrete or masonry or, more commonly, steel framing with cold formed metal studs. The means to do that is usually based on an aluminum framing system that is secured to the building structure, provides space for the insulation and ventilation, and firmly holds the cladding in place.

The entire system (cladding, substructure, insulation, AWB) also needs to meet fire safety requirements. In particular, NFPA 285 is a standard requiring the testing of full exterior wall assemblies for fire resistance and safety. This is particularly applicable if combustible plastic foam insulation is used behind the cladding since it has caused the rapid spread of fire with tragic consequences in the past. The use of non-combustible materials in the entire system helps address this fire safety concern directly.

 

The StoVentec^® Fiber Cement Ventilated Rainscreen Cladding System

With all of the variables for exterior wall and cladding systems described above, it can be quite daunting to select and specify all of the different materials and components from different manufacturers and suppliers. In response, Sto Corp. offers a pre-engineered solution that provides a complete, coordinated, code-compliant system that is available from a single-source supplier. Not only can this approach save on the cost of the overall system, but it can also speed along the installation process by a single trade using a system that is designed for ease of construction. It further means that the entire assembly can be warranted by the manufacturer when it is installed following directions and standard protocols.

The components of the Sto pre-engineered solutions are designed to provide high performance, fire safety, and aesthetics in a cost-effective, coordinated system. Some of the features that make the system more appealing than other products on the market include the following:

• Air and Water-Resistive Barrier Sto AirSeal^® is applied directly over the face of the building wall sheathing or other surface. This has been shown to very effectively protect walls against moisture damage from rain during construction and provide secondary moisture protection while the building is in service. It is a fluid applied AWRB (not a sheet applied system requiring seam sealing, etc.) designed for use on most substrates, including glass mat gypsum sheathing, wood-based sheathing, concrete, and masonry. It functions as the primary air barrier component in the wall assembly and comes with multiple transition components for maintaining AWRB continuity at joints, seams, wall penetrations, and across dissimilar materials. It has been tested to show building code compliance as confirmed by ICC-ESR 1233. It also features a superior 500% tensile elongation and meets the requirements of ASTM C1305 – “Standard Test Method for Crack Bridging Ability of Liquid-Applied Waterproofing Membrane.” Alternatively, in taller buildings or areas of extreme weather subject to higher performance demands, Sto Gold Coat^® or Sto VaporSeal^® can be used where a vapor impermeable air and water-resistive barrier is needed.
• Sub-construction StoVentro™ is the system of wall brackets, fasteners, and T and L-profile components designed to secure the cladding to the building. In addition to forming the structural link between the visible façade and the base wall, this engineered system provides better design and installation flexibility compared to other systems with more restrictive components. Adjustable brackets work to level out uneven walls, create plane changes, or assist with unique three-dimensional designs for the facade. They can also be a quality control component by accommodating substrate waviness and imperfections. The brackets support T and L-profiles that are specifically designed to create ventilation cavities that allow air circulation and drainage for the rainscreen. The brackets and profiles are available in multiple standard depths and sizes to accommodate different thicknesses of continuous insulation while still maintaining the ventilation cavity. The engineered spacing of the brackets helps assure the structural integrity of the system while also allowing minimal interruption of the thermal insulation. The system is completed with a fully engineered and coordinated set of stainless-steel fasteners and screws that avoid galvanic corrosion.
• Thermal Insulation ROCKWOOL Cavityrock^® continuous insulation is the preferred insulation for Sto rainscreen systems. This mineral wool insulation provides excellent thermal performance while maintaining non-combustible and non-flammable characteristics. It has been tested and shown to meet the requirements of a Type I insulation per ASTM C612 (CAN/ULC S-702) “Standard Specification for Mineral Fiber Block and Board Thermal Insulation.” It also performs exceptionally well when tested per ASTM E136 “Standard Test Method for Assessing Combustibility of Materials Using a Vertical Tube Furnace at 750 °C.” The sound insulation properties of the product also make it an excellent means of adding acoustic control. The mineral wool composition can resist moisture and does not deteriorate if it gets wet - once it dries in the cavity, its full insulation value is restored. Since the insulation is installed between the StoVentro™ brackets, thermal efficiency modeling has been conducted by the engineering firm of Morrison Hershfield for each of the StoVentro bracket standard types, sizes, and installation spacing. The resulting reports help designers and installers adjust insulation thicknesses in order to meet energy codes or specified U-factor or R-value requirements in the wall.
• Fiber Cement Cladding StoVentec^® Fiber Cement panels are a high-density fiber cement cladding product that is durable, code-complaint, and noncombustible making it suitable for almost any building in any location. As an open-jointed system, it demonstrates outstanding wind load resistance and low maintenance over the life of the building.

Note that there are differences between manufacturers of fiber cement cladding including the range of testing that is done to meet different standards for performance, particularly for extreme weather conditions. For example, ASTM C1186 establishes flexural strength grades from Grade I to IV with grade IV materials preferred for use, especially in taller buildings. The StoVentec^TM Fiber Cement panels are only manufactured in the high-density Grade IV category, setting them apart from other manufacturers who produce Grade II panels (more suitable for residential buildings). Similarly, supplementary performance requirements identify panels as Type A for high performance or Type B with lesser resistance to heat, rain, warm water, frost, and water tightness.

StoVentec^® Fiber Cement panels are available in a variety of finish colors, with or without a pigmented body, and smooth or light sanded textures. Standard panel sizes are 4 x 8 or 4 x 10 feet and may be installed horizontally or vertically. Custom fabrication is also possible, enabling unique shapes or patterned layouts. Fasteners for panels may be installed using visible rivets or screws, or with concealed hangers anchored to the back surfaces.

 

Sto Support Services

Selecting a cladding system goes beyond selecting the products and systems. It also means selecting a manufacturer to work with that can support the entire design and construction team. Sto Corp. offers a range of services including consultations with specifiers and installers, live construction support (both on-site and virtual), structural analysis, shop drawings, and quantity estimates. Discover more about Sto’s support services at https://www.stocorp.com/support-services/.

Overall, StoVentec^® Fiber Cement Rainscreen^® Systems meet the design needs for high-performing and fire safe building facades in a cost-effective, warrantable, single source solution. For more information about how to use this remarkable system on a current or upcoming project, visit https://www.stocorp.com/rainscreen/ or contact the company directly for personalized assistance.