Metal Buildings Grow Up Green
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Whenever facility executives hear the phrase “sustainable building,” simultaneous hope and trepidation may cross their minds. Hope that green building practices can save their organizations money and make building occupants healthier and happier. Trepidation that their organizations may fall prey to slick marketing gimmicks and hype, buying into a structure or building materials that simply do not stand the test of time.
How does one choose? And what are the best available options? Much depends upon location and the emphasis an organization places on certain aspects of green building.
Representatives from the Metal Building Manufacturers Association (MBMA) say that metal building systems are one possible answer for facility executives in the hunt for lowered construction costs, increased operational savings and durable buildings.
“Some people hear ‘metal buildings’ and think ‘tin shed,’” says Keith Fischer, chairman of MBMA. “But it is a lot more than that. We’ll build anything from five stories down, which can include aircraft hangers, commercial buildings, banks, car dealerships, churches and more.”
Today’s metal building systems are not pre-fabricated and purely utilitarian. Each building structure is custom-engineered to the end user’s needs, and designed to be energy efficient. Like tilt-up concrete construction, metal building systems also can employ a variety of wall systems and facades — not just metal wall panels.
According to Fischer, most metal building manufacturers use proprietary software to optimize the weight of steel in a building — an important consideration given recent steel cost fluctuations in 2004 and again in 2007-2008.
By employing CAD software, manufacturers create structures tailored to facility executives’ specifications.
“Conventional steel buildings use standard steel shapes,” Fischer says. “In contrast, we look at structural members to determine where the maximum stresses are and put the material where it’s needed by custom sections that vary in flange width and thickness and web depth and thickness as needed.”
Metal building structures are generally lighter-weight construction than conventional steel buildings, so the erection, foundations and site work can be made more sustainable because they use fewer resources.
“The pieces come from our factory pre-sized, pre-drilled to exacting spec,” he says. “Think of it like an Erector Set. Once on site, every one of the pieces bolts together, with little additional field cutting, drilling, welding or fabrication required.”
Most metal buildings have metal roofs, even if they do not employ metal exteriors elsewhere on the structure. One result of the construction method is that cavities exist beneath the roof and in the walls to facilitate placement of insulation.
“The most common way to insulate a metal building roof or wall is to sandwich fiberglass batts between the metal panels and the metal purlins or girts,” says W. Lee Shoemaker, director of research & engineering at MBMA. “However, the compression of the insulation over the purlins or girts should be evaluated to determine the thermal efficiency of this system. This can be done through testing or advanced computer modeling to establish the U-factors published in the energy codes.”
Purlins and girts are horizontal structural members of roofs and walls, respectively. The good news is that there are several methods to insulate metal buildings, depending on the application and depending on whether facility executives want to exceed the code-prescribed level of insulation.
Fischer says that the cost-effectiveness of using insulation in metal buildings is a big attraction for many users. Insulated wall panels are sometimes used in place of fiberglass batting because of their high R-value, he says.
Between the R-value potential and the ability to control air exchange in metal building systems, MBMA representatives say the cycling of heating and air-conditioning units can be optimized for more consistent control, thereby lowering long-term energy use and operational costs.
Cool Roofing Savings
In addition to regular participation in the Cool Roof Rating Council, the MBMA — along with three other associations — participates in The Cool Metal Roofing Coalition (CMRC).
Charles Praeger, general manager of MBMA, says that CMRC was formed to educate architects, building owners, specifiers, code and standards officials, and other stakeholders about the sustainable, energy-related benefits of cool metal roofing.
Shoemaker says the industry is seeing greater demand for cool roofing solutions, which is driving the creation of more coating options.
This increased interest has spurred collaborative research through Oak Ridge National Laboratories (ORNL).
One example of the impact of cool roofs on energy consumption was substantiated by ORNL on two nearly identical schools in the Paulding County School District in Georgia in 2002 and 2003.
The Bessie L. Baggett Elementary and Lillian C. Poole Elementary schools are the same size (90,000 square feet), have the same HVAC units and the same orientation to the sun. Each school has a standing seam metal roof system manufactured by an MBMA member.
According to Praeger, the schools’ architect and district superintendent decided to use these two schools to serve as test sites to study the value of cool roof technology in a real-world situation. While there have been studies done to show the effectiveness of cool metal roofing, this test would be a real-time study with two nearly identical sites to help quantify the findings.
Poole Elementary has a cool metal roof while Baggett Elementary was constructed with a non-cool coating. Both schools had the same evergreen roof color, a popular choice for many buildings in the area, according to Praeger. The thermostats for both schools are controlled at the district office, and were kept at identical settings for the duration of the test period. In the first year, savings were more than $8,000 at Poole Elementary. Oak Ridge National Laboratory’s Bill Miller reviewed the Poole and Baggett energy bills provided by Greystone Electric — the local utility. Miller estimated that if 10 percent of the 82,800 schools in the Environmental Protection Agency’s Regions 4, 5 and 6 — which include parts of the Midwest, Southeast and Southwest — used cool roofing products, the schools could save more than $2.3 billion over 35 years.
One of the advantages of cool metal roofing over other cool roofing products is that it retains most of its reflectivity over its life. Generally speaking, test findings indicate that the loss in reflectivity of a coated metal roof is less than 5 percent during the first three years of operation. Other roof system weathering tests have shown a loss of up to 45 percent of their reflectivity.
For urban customers, use of cool metal roofing can potentially reduce the urban heat island effect. To reduce temperature gains in specific microclimates, like big cities, Praeger says facility executives should select metal roof systems that meet ENERGY STAR requirements for low-slope roofing (2:12 or less). These roofs can be supplied in metallic coating or painted with polyvinylidene fluoride (PVDF) coatings in a variety of colors that use specialized infrared-reflecting pigments to reflect solar rays.
Given all of their benefits, metal building systems are a good choice for many organizations, say MBMA experts. Local sourcing of construction materials, lower first costs and greater energy savings are hallmarks that should entice savvy facility executives.
MBMA has found that benefits like those often make facility executives into repeat customers. “If they understand the process and have lived with the end product, they’re sold on it and will come to us, asking for another metal building,” says Fischer.