Engineering fabric-covered buildings for true sustainability

Photos courtesy Legacy Buildings Solutions Canada

By James Kumpula
Everyone wants ‘better’ things—better homes, better schools, and better quality of life—but defining what exactly constitutes an improvement is not always easy. The grass is not always greener on the other side of the fence, so attempts at making something better may not always yield the desired results. This is also true in design and construction.

For the most part, however, people agree the ‘green building’ movement is both desirable and necessary. Many building owners and operators are focused on the practical, daily advantages of green building, such as energy efficiency and reduction in operating costs. These factors make sustainability a priority for many people when building new structures, as it can provide an enhanced return on investment (ROI) of a capital project through lower energy costs and government incentives.

Natural green properties
Facilities can get a head start on achieving greater energy efficiency simply by altering the materials used to construct a building. For example, an increasing trend in industrial applications is to utilize engineered fabric. Polyvinyl chloride (PVC) fabrics generally offer high quality and durability, and the natural properties of these materials make them a highly effective alternative choice for building users seeking green improvements.

The most important characteristic of engineered fabric from a sustainability perspective is it provides high solar reflectance, which keeps the roof cooler and reduces the overall heat island effect by deflecting sunlight away from the structure. Fabric roofs also absorb less heat due to their high thermal emittance. During the summer, these properties contribute to keeping fabric roofs about 28 to 33 C (50 to 60 F) cooler than roofs built using conventional materials. The end result is a reduced need for air-conditioning or other cooling inside the building.

Although engineered-fabric roofs succesfully  reflect ultraviolet (UV) rays, some light diffusion does get through the material—and is highly beneficial. Fabric offers up to 12 per cent translucency, meaning natural light can flood the building interior, often providing more than enough working light during the daytime.

Direct sunlight produces approximately 10,000 foot-candles (fc) of illumination. Therefore, even a roof with just five per cent translucency would still allow around 500 fc to permeate the structure on a sunny day. This is significantly higher than the minimum 75 to 100 fc typically recommended to safely perform various industrial maintenance tasks.

Most buildings will still require artificial lighting for nighttime tasks, as well as to provide illumination when the sky is overcast. However, where fabric roofing is implemented, those artificial lights are rendered unnecessary during normal daylight hours. Simply by making use of the sun for natural daylighting, fabric roofs help building users take a big step toward lower electric bills and improved energy efficiency.

The structural steel beams in a rigid-frame fabric building contain about 90 per cent recycled steel.

Sustainable engineering
While fabric itself has always offered a certain level of sustainability to facilities, the structural aspects of fabric buildings have not always been ideal. Fabric structures were traditionally erected using hollow-tube, open-web truss framing. This style was adequate, serving various industries well for many years, but it became clear these structures needed to evolve to be sturdier and more durable, as well as to adhere to new building codes and regulations. The traditional style was also limited in how well it could accommodate new green building features.

A key engineering upgrade was introduced several years ago, incorporating rigid-frame engineering into fabric structures. With this method, a fabric roof can be applied to the structural steel I-beams used in conventional construction projects. This concept allows for more design flexibility when customizing the fabric structure’s alignment and overall size, and allows users to incorporate features making the building more operationally and energy-efficient.

The old method with truss systems does not allow for a continuous liner with a thermal break on the interior, meaning it cannot reduce air leakage to a minimum. This type of system also comes only in standard sizes, unlike rigid frames, which allow users to specify exact dimensions for a custom build. Further, truss systems’ arch shape leaves unusable space on the curved sidewalls, while rigid frame is flexible enough to add features such as lean-tos, sidewall doors, and mezzanines, while also maximizing floor space.

Finally, rigid frame buildings offer greater strength than truss buildings, and can be designed specifically to accommodate hanging loads. This means energy-efficient options can be added to structures—for example, full solar racks can be added to the roof, as can energy-efficient HVAC, lighting, and air filtration.

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