Sustainable Buildings on Demand

Originally engineered to solve the problems of relocatable or temporary shelter, tensioned membrane structures are now a sustainable choice for permanent, habitable structures, providing fast, energy-efficient and affordable building solutions.
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Sponsored by Sprung Instant Structures, Inc.
Celeste Allen Novak AIA, LEED AP
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Sustainable Building Components

Engineered tensioned membrane structures have several components. Modular, vaulted frames are assembled as a system braced by intermediary members. The design professional chooses a shape along a sine curve to determine the placement of the frames developing the spine of the building. The frames can be spaced approximately fifteen feet apart on center, along an unlimited building length. However, the building width is limited and manufacturers may provide the design professional with options from a smaller span, for example a 30-foot frame, up to a large clear span of as much as 200 feet. Aluminum frames extend to a peak and back and are sloped at 26 degrees for the most effective means to prevent snow or ice accumulation. The skeletal frame members are designed with opposing flanges, providing a cavity to receive the finished exterior and interior membrane as well as the insulation filling.

The materials and their environmental benefits that comprise these systems include bolted aluminum frames, architectural coated interior and exterior membranes, optional formaldehyde-free insulation packages and skylights, window and door systems.

Aluminum Substructure

Section cut of an aluminum frame member.

Illustration: Sprung Instant Structures, Inc.

Section cut of an aluminum frame member.

Aluminum is durable, long lasting and one of the most recycled metal products in today's market. Aluminum frames used as the skeletal spine are as easy to mount into place as well as they are easily de-mountable to be re-used. Connections are fitted and bolted rather than welded, as would be typical in a steel substructure. The structural system is engineered to withstand high wind loads and to shed snow.

These sub-structures are one hundred percent recyclable with no loss of quality when re-used in another product. According to the aluminum industry, which now has a partnership with the Department of Energy to reduce the energy consumption in the refining of aluminum: "In the last 50 years, the average amount of electricity needed to make a pound of aluminum has been slashed from 12 kilowatt hours to about 6 kilowatt hours. Recycling aluminum saves almost 95 percent of the energy needed to produce aluminum from its original source, bauxite ore."2

Aluminum is lighter than steel, to transport saving on overall shipping costs. Lighter freight weight, will mean less fuel consumption by the transporting systems and a reduction in carbon-dioxide emissions. Aluminum substructures are durable and long lasting; they won't corrode and can have a long life expectancy in any climate.

Architectural Membranes: Monolithic, Durable and Long Lasting

The architectural membrane of a tensioned membrane structure serves as both the walls and the roof of the exterior building system. All-weather outer membranes are delivered on-site in rolls, and winched along the frame from one side to the other using spacer bars, similar to the lofting of a sail. The membrane panels are tensioned across a spreader bar in the frame and insulation is added to the ribs as well as an interior membrane, tensioned into place by hydraulic machinery. Architectural membranes are stretched to a predetermined factor. It takes 1500psf to stretch the membrane using hydraulic rams. Manufacturers supply training and assistance to contractors as to the handling of the unique interior and exterior finish materials that are also part of the structural system.

When additional daylight is desired, a highly translucent daylight section can be chosen as a part of the membrane. The top section of the exterior and interior membranes is designed to insert a skylight along the apex of the spine of the building, providing an abundance of natural light for these high-ceiling structures.

Color on the exterior of the Warren Station at Keystone, Colorado.

Photo: Sprung Instant Structures, Inc.

Color on the exterior of the Warren Station at Keystone, Colorado

According to the American Society of Civil Engineers (ASCE) Structural Engineering Institute's Standards on Tensile Membrane Structures, a fabric is defined as a two-dimensional cloth made up of yarns or slit tapes that may be impregnated with a matrix that binds them together. The yarns may be woven or laid, frequently coated or laminated. Membranes are defined as the flexible, coated, or laminated structural fabric of film that supports imposed loads and transmits them to the supporting structure.3 The membranes in a tensioned membrane structure carry only tension or shear in the plane of the membrane. Although tensioned membrane structures are engineered to have some movement in the frames, because the membranes are tensioned across spacer bars, there are no wear-points. When it is time to replace the membrane, sections can be replaced in segments without exposing any interior furnishings or fixtures. The strength or tensile properties of the finished coated membrane is controlled by its polyester base cloth. The PVC coatings are provided to protect from UV degradation of the fibers in the base cloth and to provide a weather barrier. An acrylic coating is specified to provide protection against Ultra-violet (UV) rays as well as airborne contaminants and pollution. For additional protection and a longer life cycle to UV and airborne contaminants, additional coatings such as Kynar, a PVDF film, can be added to the membrane which helps reduce the impact of weathering on the surface. An architectural membrane is a fabric but unlike a tent product that may be expected to have a short-term use, primarily as temporary shelter, engineered materials can be used as habitable buildings for many uses.

Illustration of a green membrane.

The next generation membrane coatings or films are top-finished and coated with Kynar an advanced form of polyvinylidene fluoride or PVDF. Kynar is a finish that architects have used for over forty years, on metal buildings and in high-end paint products. Applied as a film to membrane surfaces, Kynar provides superior resistance to staining, dirt and mildew growth as well as increased color retention, gloss and membrane life expectancies approaching 30 years. Membranes can be a solid color and printed with any logo, or symbol, or decorated with accent lines and patterns. They can be selected in multiple colors. Patterns and wave designs can be created using membranes.

Marshall Aerospace, Cambridge Airport.

Photo: Sprung Instant Structures, Inc.

White interior lining is the finish, as well as the interior membrane, at Marshall Aerospace, Cambridge Airport.

Architectural membranes weigh from eighteen to thirty-two ounces per square yard, making them one of the lightest building envelope finish materials available to a design professional. The heavier materials can be specified for increased load requirements. Additional savings on fuel and emissions for transportation of this material are gained by using architectural membranes. An engineered membrane is not only the exterior surface of the building; it is also the finished surface of the interior walls and ceiling. Contractors and installers will require jobsite quality standards for handling these membranes to avoid scratches or blemishes on this interior wall and ceiling material.

Insulation: Airtight Membranes

Insulation provides comfort in both hot and cold climates. Insulation reduces the cost of climate control as well as absorbing sound for better acoustics. A comprehensive insulation package for a tensioned membrane structure includes vapor barriers, thermal breaks and a tensioned, finished interior liner. Additionally, membranes are designed to have low air and vapor permeance.

A structure with a lattice beam frame that is merely filled with insulation can leave unvented dead air spaces, creating the opportunity for the spread of mold, mildew and fire. In any building, holes in the insulation can dramatically reduce its performance and multiple layers of insulation may merely add to dead air spaces between each layer, negating much of the insulation value. Retaining the insulation within a cavity is crucial and in some membrane structures, insulation has been known to slide down the roof and bunch at the base of the wall.

Designed to accept a sandwich of fiberglass batting, insulation in a tensioned membrane structure, as in any green building, can be specified with fifty-five percent recycled postconsumer glass. Every day, over 120 tons of recycled glass, normally bound for the landfill, is melted down and utilized in the manufacturing of the insulation. In addition, an acrylic resin is substituted in the manufacturing process to ensure no phenol-formaldehyde or ammonia emissions are created.

According to the EPA, "Formaldehyde, a colorless, pungent-smelling gas, can cause watery eyes, burning sensations in the eyes and throat, nausea, and difficulty in breathing in some humans exposed at elevated levels (above 0.1 parts per million). It has also been shown to cause cancer in animals and may cause cancer in humans."4 The EPA has been working to reduce the use of formaldehyde in building products as research continues to mount as to the hazards of formaldehyde in insulation products.

Most environmental rating systems, such as Green Globes, USGBC LEED®, BREEAM, and the California High Performance Standard, give credit for indoor air quality and materials that prevent volatile organic compounds from being off-gassed into buildings by building products. Formaldehyde-free insulation improves air quality, and adds to the evaluation of a green building.

Engineering: Daylight and Views

As previously mentioned, these structures are engineered to receive optional skylights that straddle the spine of the building. Skylights provide a highly translucent interior glow to the finished building with relatively minimal heat loss. In addition, energy-efficient windows and doors can be added to these structures to provide direct daylight and views. Connections to other buildings, new lobbies and entries are all potential daylighting opportunities for the design professional.

An example of integrated daylight strategies at the Sprung Campus in Calgary, Alberta.

Photo: Sprung Instant Structures, Inc.

An example of integrated daylight strategies at the Sprung Campus in Calgary, Alberta.

Ravenna Golf Club needed a banquet and tournament facility to increase revenue and considered erecting a conventional tent building. After seeing the very latest insulation and glazing wall systems provided by tensioned membrane structures, the club chose an alternative that met the aesthetics they required in a permanent structure.

 

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Originally published in Architectural Record
Originally published in December 2010

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