November 8, 2019
by Jim Leslie and Kevin Smith
Wind-driven kinetic façade systems add dynamic movement to building enclosures and wall systems. Responding to air currents, the flapper-panel design creates the look of rolling waves across the wall. Suitable for small- and large-scale projects, popular applications are transit and parking facilities, cultural institutions, entertainment venues, and artistic installations.
A kinetic structure effectively alters the environment around its installation and, in turn, the structure is also affected by its surrounding conditions. The façade system, therefore, will need to possess specific design measures to ensure the building structure, as well as the occupants, are in harmony with the existing enclosing environment.
When considering a kinetic façade installation, several site-related factors should be taken into account to ensure the chosen system functions as intended. The geographical location of the building is one of the most crucial aspects of successful kinetic façade design, specification, and installation.
Some location-specific questions that need to be considered during the conceptual design stages are:
Also essential is the building’s orientation, the position of the structure relative to the surrounding environment. How the orientation affects airflow, façade visibility, and the fall of direct and indirect light at various times of the day should be assessed to ensure maximum performance.
Following an analysis of the building’s orientation, the viewing perspectives of the kinetic façade need to be considered. In other words, at what vantage points and viewing distances can the façade be observed for maximum visual impact? For instance, in tight urban environments, where most vantage points are nearfield, small flapper elements should be considered to achieve a denser, less pixelated appearance. Conversely, for installations where the façade will likely be viewed at greater distances, larger flapper sizes can be used to achieve the same visual impact at a lower cost. Additionally, if the kinetic façade serves as a shading device, the aesthetic appearance of the system from within the building may also need to be taken into account.
The solar angle, and its effect on selected materials and associated glare, is another factor in the design, specification, and installation of kinetic façades. The angles at which sunlight strikes the façade’s elements can have a profound impact on the aesthetic. For specific environments, such as those near airports or in tight urban settings, glare resulting from the selection of highly reflective materials may be undesirable. In other cases, where indirect light is predominant, a material with more reflectance can accentuate the façade’s kinetic activity.
Finally, while the physical properties of the façade’s elements and its interaction with the surrounding environment are critical, property/setback limitations, and zoning/code considerations need to be assessed during material selection and installation. With respect to setback limitations, the appropriate cadastral map and other relevant property documentation should be consulted to ensure the flappers have enough clearance to exhibit a full range of motion without violating requirements.
Additionally, all local zoning ordinances should be thoroughly researched to determine what, if any, regulations apply. For instance, some municipalities may require façade installations to comply with sign ordinances, especially where lettering or designs are applied or expressed through the arrangement of colored flappers. Other jurisdictions might have restrictions on moving elements. In applications where the kinetic façade panels also serve as guardrails, they must be designed, specified, and installed in accordance with the relevant safety standards and specifications. For buildings, such as garage structures, where codes and standards specify free air ventilation requirements, the façade panels and elements should be sized to meet these needs.
All kinetic installations can produce some level of ambient sound under higher wind conditions, therefore, the chosen system should not generate sound considered to be excessive for the given environment. The suspension system, construction material, and flapper geometry can be adjusted to ensure the level, tone, and timbre of the resulting sound is acceptable. Many manufacturers engineer systems with the flappers to reduce the collateral noise. It is, however, crucial the volume and quality of sound generated by the installation are considered as early as possible in the design and specification process, and are verified with full-scale mockups.
Like any reachable structural element of a building, a façade is vulnerable to vandalism. The accessibility of the façade and the nature of the installation area should be assessed to determine the susceptibility of its elements to such issues. Ground-level elements should be given particular attention, especially if they are within reach of pedestrians. In parking structures and other applications where façade elements are easily accessible, it may be worthwhile to install protective mesh on the rear of unitized sections to prevent malicious vandalism, or to apply anti-graffiti coatings on the flapper elements. In any case, the ease of flapper replacement should be considered.
Proper kinetic façade design should discourage bird or insect nesting. Minimized fixed horizontal surfaces, no open hollow voids, clear openings between the moving elements, appropriate suspension systems, and reflective materials, are just some of the measures that can be employed to deter bird nesting.
While every challenge of site location, orientation, and environmental surroundings cannot be predicted, addressing the above considerations will set a kinetic façade project on the path to success.
Performance requirements are important on every building, and deserve extra attention with kinetic façade systems. Careful analysis is needed regarding the interaction between the kinetic façade elements and the building structure to which it is attached, as well as the impact of the structural behavior on the design and cost of the system.
Structural loads, especially those due to positive and negative wind pressures, need to be assessed to ensure the façade system meets the required strength specifications and the aesthetic requirements. Ice, snow, and seismic loads are also influential in the specification, design, and installation of the kinetic façade.
The method of attaching the façade elements to the building needs to be examined and coordinated as early as possible during the design and specification phase. For example, will the kinetic panels be self-supporting, or will secondary supports need to be installed? In concrete structures, this means evaluating their embeds and anchors, their interaction with the existing reinforcement configurations, and the required supporting system.
The kinetic façade system also needs to be compatible with anticipated building movements. The attachment design should account for the dynamic deflections of various types of buildings and structural systems. In parking structures, for example, the dynamic deflections from vehicle traffic must adequately be taken into account. Kinetic façade systems that cannot accommodate the required deflections run the risk of failure. It is, therefore, crucial mounting systems are designed for these deflections to ensure long-term integrity of the system is maintained. Close coordination between the façade designer, manufacturer, and the engineer of record (EOR) for the supporting building structure is critical even in the early phases of the design process.
A building’s structural demands may also govern the testing requirements of the kinetic façade. These testing requirements are often driven by local codes. However, they may also be determined by the desired façade performance. Some are ASTM standards, such as ASTM E330, Standard Test Method for Structural Performance of Exterior Windows, Doors, Skylights and Curtain Walls by Uniform Static Air Pressure Difference. Others may be custom to the project as required by the client or local jurisdiction.
Design and specification considerations
With a kinetic façade system, the focus is on material selection, the flapper elements’ size, shape, and spacing, and the suspension systems supporting them. Integration of lighting elements also can play a critical role in the system’s design and the project’s final appearance.
As with any façade, material selection and arrangement is critical to long-term performance of the system. Due to the dynamic nature of a kinetic façade, it is critical to incorporate movement and, therefore, to wear the proper selection of ultraviolet (UV) and abrasion-resistant material. This often involves customized, accelerated testing of components and assemblies. Some materials are provided to the faced system manufacturer with testing, such as UV-resistance. Other tests, such as abrasion and wear, may need to be conducted by the manufacturer.
Physical mockups are also important during the developmental phases to assist the design team, building owner, and sometimes, the authority having jurisdiction (AHJ) in understanding the visual and auditory effects of the proposed façade.
Flapper and lighting elements
Wind-driven, dynamic façade systems support a variety of flapper shapes, sizes, and materials. While aluminum is the most popular, other options include perforated materials, stainless steel, polycarbonate, polytetrafluoroethylene (PTFE), acrylic, and even polyvinylidene fluoride (PVDF) films.
Multiple flapper finishes are also available. Standard finishes include anodized aluminum or fluoropolymer paint. Higher gloss finishes, such as metallics, tend to shifting and textured finishes also produce interesting visual effects.
Patterns can be printed or perforated on flapper elements. This can range from basic screen printing of simple patterns to full-color image printing. Large images can be segmented or pixelated across the entire kinetic façade to bring a dynamic appearance to an artistic or branded image.
Flapper elements fabricated from translucent materials allow for natural light to pass through the façade. Translucent acrylic and polycarbonate materials can be specified with infrared-blocking coatings to help manage unwanted solar heat gain inside the building.
Anti-reflective coatings on polycarbonate materials can reduce glare during the day, and at night could act as a backdrop for projected images and lighting effects. Regardless of the flapper element’s material composition, many kinetic façade installations incorporate illumination during the evening. Face lighting from above can be used to emulate a daytime view, while dramatic effects can be achieved through the use of various night lighting, including backlighting, uplighting, or wall wash lighting.
To accommodate the specified flapper elements, there are three typical suspension systems that must be considered for wind-driven kinetic façade designs:
Each configuration possesses different performance and aesthetic characteristics and also baseline costs. Modified and custom systems also can be developed for unique project requirements.
For ease of delivery and installation, each of these motion systems usually is factory-unitized. Dimensions commonly range from 1 x 1.2 m (3 x 4 ft) to 1.5 x 3.7 m (5 x 12 ft) in vertical or horizontal orientations.
For optimal cost and performance value, the drop-in suspension system is recommended. In this configuration, T-shaped kinetic flappers are easily inserted into a specially designed ‘rung’ extrusion system, significantly reducing the amount of time and labor required for fabrication.
The pin-mount suspension system allows the flapper elements to seemingly float in front of the support rungs and side rails as a veil. This configuration minimizes the appearance of the supporting structure. The pin-mount system allows for mixing flapper shapes to create geometric patterns and for installation at various mounting points, facilitating changes in kinetic activity.
Drop-in and pin-mount suspension systems allow the flappers to be removed and replaced without any specialized tools if repair or maintenance is needed. Both systems also accommodate up to a 90-degree range of motion.
Offering a 360-degree range of motion for the individual flappers, the rod-mount suspension system allows for greater intermittent views through the kinetic façade and minimizes the appearance of the horizontal supporting structure from within the building. They can also permit increased airflow and promote passive cooling. The vertical side rails are typically more prominent within the façade and the flappers can be replaced with simple tools.
Some manufacturers also offer cable-mount suspension systems. These systems suspend the kinetic elements or flappers between a combination of horizontal and/or vertical cables. The flapper replacement for cable-mount systems can involve costly and time-consuming restringing or replacement of the entire cable section.
A project’s design and specification phase is the best opportunity to critically analyze the aesthetic and performance requirements, and to make adjustments to ensure its success. Once the project moves into fabrication and installation, corrections become more costly.
Budgeting for a kinetic façade system usually entails striking a balance between the desired aesthetic and performance goals of the product. Since kinetic façade systems are delivered to a jobsite in pre-assembled units, most installations range from $9 to $15 per 1 m2 (11 sf), depending on several factors. Note this does not include material cost.
Additional costs also may be incurred as a result of testing requirements of the location or the application. Local labor costs, union requirements, site access, street closures, timing and scheduling, and project duration, are just some of the installation-related factors that can affect the final cost of kinetic façade systems.
In addition to the costs associated with installation, system type, and testing, other relatively small hardware or structural changes can have a profound impact on the final cost. These include the following.
Flapper density is defined as the number of flappers per 1 m2. The smaller the flappers, the more individual handling, assembly, labor, and mounting parts are required. For example, it would take about four 130 x 130 mm (5 x 5 in.) flappers to fill a 1-m2 area, assuming a 25-mm (1-in.) space between flappers, while it would take nine 76 x 76 mm (3 x 3 in.) flappers to fill the same area. This increased number of flappers translates to more than double the amount of assembly time, labor, mounting hardware, etc.
Flapper elements produced from pre-finished sheet material, such as anodized or painted aluminum, typically are more cost-effective than post-finished flappers. The type of finish also influences the overall cost of the kinetic façade. For example, standard anodize and painted colors will be more economically priced than exotic colors and multistep coatings. The cost and benefits of each type
of finish should be analyzed to ensure the flapper finish does not adversely affect the project budget.
Finish on back of flappers
Finishing the back-side of flappers can incur additional costs because it requires the use of extra material and resources. Anodized flappers will have both front and back faces coated with the same process. Painted flappers, on the other hand, can accommodate different coatings on the front and back face. While both sides can be coated with the same finish, opting for a wash coating on the rear face may reduce overall cost. This painting method is acceptable on the back side of the flapper when it is either invisible or barely visible, which will be the majority of applications.
Supporting structure finish
In addition to the finish on flapper elements, the finish applied to the supporting structure, (i.e. the horizontal and vertical mounting rails), also influences the cost of the total façade system. A darker, low-sheen finish is applied to the supporting elements to accentuate the aesthetic quality of the flapper elements. These framing members are usually painted.
Building spans and loads
The required span and environmental loads can affect the weight and size of the kinetic façade’s structural elements. This can, in turn, impact the cost of the system.
The mounting hardware and anchoring systems of the flapper elements depend heavily on the required span, deflections, and building substrate materials. This hardware can consist of embeds integrated into the building structure or post-applied anchors supplied by the façade system manufacturer.
Manufacturer and installer considerations
Given the complexity of kinetic façade systems, it is advisable to seek out an experienced designer and manufacturer to participate early in the project’s design and specification. It is recommended to look for one offering preliminary cost estimating, mockups, and a variety of fabrication and installation options to meet each project’s functional and aesthetic requirements. Some manufacturers will also manage all aspects of the installation process, providing a single-source price directly to the building owner or general contractor (GC).
For maximum cost efficiency, a kinetic façade manufacturer may be willing to deliver its services solely as a material supplier. With this solution, materials are provided directly to a local installation contractor already involved with the project, such as a glazier, curtain wall installer, roofer, or GC. Startup supervision and initial training for installation crews may be included as part of these services.
In the role of a material supplier, the façade system manufacturer may also offer pre-bid support. Generally, this involves formally presenting the system, its installation processes, and other relevant documentation to the prospective GCs and/or installers. Regardless of the tendering process, formally presenting the product ensures prospective bidders have a thorough knowledge of the system, eventually resulting in better quality and more informed bids.
Once the bid is approved and the contract awarded, a successful installation of a kinetic façade is measured in terms of time, cost, and quality. It requires the synergistic coordination of various activities including design, engineering, testing, fabrication, delivery, and installation. This begins during the conceptual design phase, with the development of the project schedule.
Typical project durations range from 12 to 20 weeks from the time of award. The type of overall design, the complexity of the kinetic elements, and the scope of the installation are some of the factors affecting this timeframe. For large-scale kinetic façade systems, delivery schedules often are phased at various construction stages to allow a continuous stream of material through the duration of the installation. This phased method of delivery avoids potential damage to components stored on site and helps conserve space by limiting site laydown and storage areas.
The kinetic façade installation is arranged as one of the final undertakings during building construction, thus limiting the exposure of the façade elements to potentially damaging activities from adjacent trades.
With the installation complete, minimal manual cleaning is required—naturally occurring rainfall is typically sufficient. In situations where more advanced cleaning is desired, mild pressure washing can be employed. While there are no routine maintenance requirements for most kinetic façade systems, periodic inspections for issues, such as storm damage or vandalism, and mounting connection checks are recommended.
With early involvement and ongoing collaboration between the designer, specifier, installer, and supplier, wind-driven kinetic façade systems add a dynamic and distinctive element to parking garages, retail centers, museums, sports arenas, theaters, and other building structures.
Jim Leslie is the general manager of EXTECH/Exterior Technologies, Inc., in Pittsburgh, Pennsylvania, leading the company’s mission to improve lives through innovation in daylighting systems, natural ventilation, and other building envelope systems. Working closely with architects and specifiers, Leslie and his team redefine the intersection between the natural and built environments with wall, window, skylight, canopy, and custom systems such as dynamic façade designs. Leslie has a bachelor’s degree in mathematics from Penn State University and is a member of the American Production and Inventory Control Society (APICS). He can be reached at email@example.com.
Kevin Smith is a registered architect, and leads EXTECH’s team of architects and engineers as director of product application and development. He brings more than three decades of experience in designing commercial, civil, industrial, and transportation projects, as well as daylighting, static, and kinetic façades. He earned a bachelor of architecture degree from Carnegie Mellon University. He can be reached at firstname.lastname@example.org.
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