Launch Slideshow

Increasing the energy-efficiency of fabric roofs

Increasing the energy-efficiency of fabric roofs

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    Legacy Building Systems

    Rigid-frame engineering allows more design flexibility, including features that are more operationally and energy efficient. In 2010, Legacy Building Solutions became the first fabric structure manufacturer to incorporate structural-steel beams in a rigid-frame building design. The structural steel I-beams in a typical rigid-frame building contain almost 90% recycled steel.

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    Insulation and interior fabric liners can help achieve building energy codes, while still allowing a fabric skylight to provide ample illumination inside.

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    Due to fabric’s high thermal emittance and solar reflectance, fabric roofs can stay about 50° to 60° F cooler than conventional roofs.

The inherent beneficial properties of polyvinyl chloride (PVC) and polyethylene (PE) fabrics — i.e., high solar reflectance, high thermal emittance, and up to 12% translucency (see sidebar on next page) — have always existed, making fabric ideal for salt and sand storage, waste/recycling, maintenance, and other facilities.

In recent years, engineering innovations — primarily, using structural steel beams rather than hollow-tube, open web-truss framing for rigid-frame designs — enable much more flexibility vis-à-vis fabric building size, alignment, and customization that will make the building much more energy-efficient. Many of these additional benefits are related to the roof.

Temperature control. A traditional architectural design that gives a fabric building significantly more strength, rigid-frame engineering makes it easier to add items like interior liners and insulation to the roof and sidewalls. A temperature control barrier of approximately R-5 can be achieved simply by using an inner fabric liner in addition to the main fabric skin. The inner liner is often a lighter-weight fabric, since it is not exposed to wind and snow loads.

Combining the inner liner with insulation, such as Owens Corning’s Pink Panther batt insulation found in most homes, produces an insulation value of up to R-40. This level meets almost all relevant U.S. energy codes, providing significant heating and cooling cost savings over uninsulated structures.

Fabric building manufacturers offer both liners and insulation as options.

Daylighting. An insulation package may dictate covering much of the structure’s translucent fabric. However, the building manufacturer can add enough insulation to achieve energy codes while still leaving a large enough portion of uncovered fabric as a skylight to provide ample illumination levels inside.

Ventilation. You can mount fans or heavy-duty ventilation systems on a rigid-frame structure if necessary, but another option is a gravity ventilation system that relies simply on air movement. As hot air rises, it works with pressure intakes around the perimeter of the building at the base and a gravity ventilator at the ridge to create circulation inside the building. By providing a natural intake for fresh air and an evacuation point for fumes without the need for powered equipment, specifiers save on energy consumption and operating costs.

Most fabric building manufacturers offer these systems as options. The cost difference between electrically powered ventilation systems and gravity ventilation systems depends upon building size, local environmental conditions, and intended use of the building. However, gravity systems typically cost 25% to 30% less.

Solar power. Building owners can specify solar panels to further reduce dependence on man-made power, in some cases enabling the building to fulfill all of its energy needs. If your fabric building manufacturer does not offer solar options, you can also purchase solar panels from solar technology companies like PowerFilm Inc.

An emerging trend still being tested by some manufacturers involves the use of a thin-filmed photovoltaic adhered directly to the building’s fabric panels. A less sophisticated system for solar heating in the winter uses perforated metal to capture hot air in a cavity and bring it into the structure. Traditional crystalline or silicon panels can be incorporated within a building design as well.

Water capture and reuse. Attach basic gutters and downspouts to direct rain into cisterns for later use around the facility when water is needed. Although these standalone systems aren’t offered by most fabric building manufacturers, they can be incorporated into the overall building design. You can purchase cistern systems through rain harvesting/stormwater management companies like Randrop Cisterns Inc.

When it comes to the green movement, most industries still find themselves abiding by the 80/20 rule — 20% of end-users and manufacturers recognize the importance of energy and resource management and are trying to drag the other 80% along for the ride. But as more building owners experience the long-term energy savings that put more “green” in their pockets, the number of sustainable structure designs should really take off … and never look back.

Tom Ruprecht (tomruprecht@legacybuildingsolutions.com) is director of Legacy Building Solutions, based in South Haven, Minn.


‘Green’ plastic: polyvinyl chloride (PVC) and polyethylene (PE) roofing

Fabric structures offer a high solar reflectance, keeping the roof cooler and reducing heat-island effect by reflecting sunlight’s heat away from the building. Tension fabric’s high thermal emittance also contributes to the roof, absorbing less heat. During peak summer weather, these properties combine to keep fabric roofs about 50° to 60° F cooler than roofs built with conventional materials, thereby reducing the need for temperature-control measures inside the building.

Fabric roofs also offer up to 12% translucency to allow natural light to permeate the structure. Direct sunlight offers about 10,000 footcandles of illumination, so even 5% translucency will let approximately 500 footcandles into a building on a sunny day — well above the recommended 75- to 100-footcandle guidelines for maintenance of machinery and other tasks.

Most facilities will still need artificial lights for nighttime work, and to provide adequate illumination on stormy or overcast days. During normal daylight hours, however, fabric roofs effectively eliminate the need for artificial lighting. This helps to reduce your electricity bill, and makes a building more energy efficient. These benefits also help to rapidly accumulate points on the path to LEED certification.