The installation of the factory-rollformed metal roof system, along with trim, curbs, flashing and a final layer of insulation, took a crew of five men 12 days. The crew also was responsible for setting sensors for the Oak Ridge National Laboratory data-acquisition system and adjusting solar purlins for the solar-thermal system directly beneath the metal roof surface.
Dynamic heat transfer will optimize the thermal performance of the entire system. Any heat that is transferred from the outer roof is useful to the solar-thermal water-heating system located between the old and new roof surfaces. As the heat is absorbed into the water/ glycol heat-exchange medium in the solar-thermal system, it reduces the heat that could otherwise flow into the building space beneath the roof system. The space between the two roof surfaces also allows for natural convective cooling by dissipating residual heat out of the ridge vent, rather than allowing it to become part of the solar gain into the building.
Cool Roofing
Cool metal roofing technologies are described in The Whole Building Design Guide (WBDG), a document with a goal of creating successful high-performance buildings by applying an integrated design and team approach during the planning and programming phases. Because DoD and other government agencies follow the WBDG, cool roofing technologies are an important aspect of their buildings.
Today’s metal roof coatings and paint finishes are more advanced and durable than ever before. Alloys of aluminum and zinc have replaced the basic galvanized- coated steel that was once the mainstream of agricultural and light-commercial buildings. More corrosion-resistant metallic coatings and durable paint finishes resistant to fade and chalk now offer architects and building owners unlimited design opportunities.
Galvalume sheet steel, which was used on Goodfellow AFB’s test roof, is protected with a 55 percent aluminum-zinc alloy hot-dip coating to provide excellent corrosion resistance. Inspections of Galvalume roof installations since its introduction to the marketplace in 1972 have suggested the estimated service life of this type of metal roof will exceed 60 years in most climates.
The Goodfellow AFB roof is Energy Star-labeled and listed on the Oakland, Calif.-based Cool Roof Rating Council’s directory. The paint finish is a polyvinylidine fluoride formulation, using special ceramic pigments that are highly reflective in the infrared solar spectrum. Using cool technology in paint finishes allows for darker colors, such as the medium bronze used on the Goodfellow AFB retrofit, to reflect significant levels of solar energy. The cool roof can significantly lower the surface temperature of the roof and the space beneath by reflecting more solar energy from the surface, which helps lower the air-conditioning load on the building. Combining the synergistic effect of a cool roof surface with rooftop photovoltaics also extends the life and efficiency of the solar-energy system atop the air force base’s roof.
A Turnkey Package
A holistic retrofit roof system is appropriate for a variety of building types, occupancies and climate regions. Integrated building systems, when applied to the DoD infrastructure and/or the commercial building market, can dramatically contribute to reducing energy and water consumption by providing retrofit roofing, insulation and ventilation improvements along with renewable-energy systems in a turnkey package. In addition, a turnkey package requires all trades to work more interdependently under a single supplier that is responsible for greater performance and warranty accountability.
Combining the strength and aesthetics of painted metal roofing, as was specified for Goodfellow AFB, offers a strong, durable platform for the renewable-energy systems integrated into the retrofit application. The retrofit roof system also becomes part of the sustainability theme at Goodfellow AFB. By extending the life of the roof, reducing the replacement cycle and thereby lowering the environmental impact of using virgin material for replacement roof products, DoD is closer to meeting its conservation goals.
PHOTOS: Goodfellow Air Force Base
Metal roof supplier:
MBCI, www.mbci.com
Online Buzz
View a video (upper right) that provides an overview of the energy-reduction program at Goodfellow Air Force Base, San Angelo, Texas.