by Peter Fervoy
A roofing system’s function is to protect the area beneath it and the building’s occupants from the elements. Traditional, static roofing must be strong, resilient, and code compliant. Temporary roofing systems offer a myriad of benefits for commercial applications, and can be an alternative for building owners who want to create their outdoor spaces with potential for year-round use, subsequently allowing them to continue to generate revenue even when the weather is not ideal.
Outdoor dining and entertainment spaces are becoming more popular as the demands of work and everyday life increase. In the rush of daily life in the 21st century, people are increasingly making up for time spent working by grabbing opportunities to break away from the rush and recharge in the sun and fresh air, while enjoying the serenity of a beautiful view.
As the hospitality industry seeks more ways to utilize outdoor spaces to meet this demand, the architectural community likewise has sought ways to blur the line between indoors and outdoors in order to satisfy their client’s needs. In expanding the programmed space to the outdoors, architects are required to find a way to maintain the open sky when weather permits, yet provide reliable protective cover in case of rain, wind, or excessive sun.
In the past, people found the answer in custom designed lightweight retractable fabric roof systems. These assemblies tended to be cost-prohibitive to build. Eventually, with technological advances and extensive research, knowledge, and testing, a more durable retractable awning system was developed. This kind of retractable tensile structure utilizes the same technology and programmable systems as large-scale, stadium-sized retractable awnings. They can be deployed at the push of a button, and are efficient to design, supply, and install to fit within available budgets and schedules. Ultimately, these highly engineered retractable awning systems offer the same level of sophistication as in any major facility around the world.
According to Nic Goldsmith, senior principal, FTL Design Engineering Studio, small-scale retractable systems, utilizing similar engineering as larger, mainly commercial systems, are increasing in popularity and in light commercial applications in places like Florida where the weather can change often, and temporary protection can be obtained quickly and easily.
The engineering, design, higher wind loading, and finesse of highly advanced retractable awnings makes them applicable in high-end, challenging, or tricky areas like Miami.
A retractable awning with advanced engineering and resilience is typically a fully automated, motorized covering system developed to behave as a true tensile membrane structure, with configurations capable of withstanding winds up to 145 km/h (90 mph) and combined loads of a maximum of 147 kg/m2 (30 psf), provided the structure and collateral framing is properly designed and installed. With a clean and strong modular design, these awnings can be feasible for use in a wide variety of locations, such as restaurants, shopping centers, homes, stadiums, or other gathering spaces.
Extremely resilient awnings can comply with stringent codes in cities like Miami, where temporary roofing is a boon to businesses relying on outdoor spaces to attract and retain customers.
On an effective large-scale retractable system, the fabric must be tight, and heavy machinery and big motors are used to put thousands of pounds of tension on the fabric. The tension adds a lot of strength to the system and all the parts, and this illustrates the complexity and durability, which would generally not be seen on something similar used on a small scale. A highly advanced system can even have benefits similar to a static roof, to the extent that one can walk on it.
On awnings such as these, mechanization equipment can consist of a toothed belt drive acting as both the means of extension of the fabric and final tensioning device of the membrane. The toothed belt circulates around an arrangement of pulleys. As the motor turns, it circulates the toothed belt and moves the driving carriage back and forth along the internal guide ways of the drive beams. The beams also serve as primary support members and act as the enclosure for the mechanization system. The leading-edge beam that is lying perpendicular to the primary support member is attached to the bottom of the driving carriage as well as to the leading edge of the fabric membrane. Additional idler beams lay parallel to the leading-edge beam and are spaced at intervals based on the custom size of the unit. The structural fabric membrane is divided into long strips and then wrapped around an extruded polyvinyl chloride (PVC) core to effectively fasten to the idler beams. This exposes the fibers on the outside and allows the edge of the retractable fabric membrane to easily slide. The corners of the fabric panels are cut with a catenary curve and have a small diameter stainless steel cable rope hemmed into them. As the driving carriage is tensioned by the toothed belt, the catenary cables in the ends of the fabric panels are tensioned, thus producing tightness in both directions. This bi-axial tension gives the fabric its capability to perform as a structural element. Water is allowed to flow unobstructed over the tops of the idler beams when the system is in an inclined position.
Highly engineered and advanced retractable awnings can withstand thunderstorm winds (i.e. 169 km/h [105 mph] with a three-second gust). When there is a named storm or hurricane, the roof must be retracted.
With advanced technology in mind, some retractable awning systems may also have variable speed controls and the belt drives can be synchronized through continual monitoring of the absolute encoders in each motor. When the system reaches full retraction, it will shut down based on counts from the encoders in the motors.
The unique design of such systems fully resolves all of the fabric pretension forces within the aluminum drive beams and the perpendicular idler beams. This means they do not impose high loads into the surrounding architecture, making it a solution for retrofits in existing structures as they require little or no reinforcement. Further, with corrosion-resistant aluminum construction and a robust mechanization system, some retractable systems can be designed to perform reliably for years even in harsh coastal environments such as Miami Beach.