PROFESSOR OF ARCHITECTURE, THE UNIVERSITY OF TEXAS AT AUSTIN

The U.S. is facing critical energy problems characterized by rising energy prices, declining productive capacities for oil and an increasing reliance on foreign oil. According to the U.S. Energy Information Administration (EIA), the U.S. is currently spending $547 billion a year — or $1.52 billion a day — to import oil. Compounding this problem has been the crippling effects of the so-called Great U.S. Recession and its accompanying severe reduction in building construction. The depth of the construction industry slowdown is severe. The industry has lost over two million U. S. jobs since November 2007. Construction unemployment is near 20%, with one in five construction workers out of work.

Because the building sector currently consumes nearly half (49%) of all energy produced in the U.S., investing in energy reductions in the building sector is the most cost effective way to generate new jobs, revitalize the stagnant U.S. economy and reduce our dependence on foreign oil, according to architect Edward Mazria, director of the 2030 Challenge.

Mazria calculates that for every $1 billion invested in non-residential repairs in the building sector, 19,300 new jobs could be generated, and for an investment of $42.1 billion in building energy efficiency, 1 QBTU of delivered energy could be saved. This energy savings would be equal to the amount produced by 235 coal-fired power plants costing $104.5 billion.

Building energy efficiency savings costs are far less than building new energy sources such as coal, natural gas, fuel oil or nuclear plants and the reductions can be implemented immediately by providing incentives for sustainable green building design and energy efficient construction and by assuring actual savings through the U.S. Green Building Council (USGBC), Leadership in Energy and Environmental Design (LEED) rating system. The rating system has helped shape the green building movement in North America in the last decade and addresses most building types, including new construction, existing buildings, commercial interiors, core and shell, operations and maintenance, homes, Neighborhoods and specific applications such as retail, multiple buildings, campuses, schools, healthcare, laboratories and lodging. Each of the building categories encompasses a broad range of goals from water and energy efficiency to environmental impacts. Natural stone products can play an important role in these green building and LEED certifications.

Natural stone products, such as those made from granite, marble, slate, sandstone and limestone, among others, have many innate attributes that can make a significant contribution to points scored in any construction project’s LEED certification. These attributes include the fact that stone has a very low embodied energy content; is a readily available natural material — often locally available (within a 500- mile radius) — does not off-gas so it’s good for indoor air quality; has a high thermal capacitance so it makes a good thermal heat sink; and because stone is so exceptionally durable, it lasts a long time with very little maintenance; and ultimately, most natural stone products are reusable.

MINIMAL EMBODIED ENERGY USE

Natural stone was created billions of years ago, so in contrast to other materials such as aluminum, steel and glass, natural stone does not need to be manufactured using a large amount of fossil fuels. The primary embodied energy (EE) expenditure of natural stone is limited to cutting stones at the quarry, applying the desired surface finishing and transporting the stone to the construction site.

Embodied energy (EE) is the amount of energy that goes into manufacturing, using and disposing of a product over its lifecycle. The energy used to manufacture, operate and dispose of building materials comes mostly from fossil fuels, so there is a correlation between the EE of a product and the greenhouse gases emitted over the lifecycle of a building.

Environmentally aware builders should consider the upstream-embodied energy costs of natural stone starting from how it is mined at the quarry through how it is delivered to the construction site. For example, what are the EE costs at a stone quarry? Is the stone extracted using energy-efficient diamond wire cutting and wedging or is blasting required? How is dust controlled during cutting? How is silting controlled to prevent pollution of surrounding waterways? Does the quarry use flocculation in sedimentation ponds to control mining slurry wastewater? Is the scrap stone collected at the quarry site and marketed for other purposes, such as landscaping, erosion control or construction base and fill? How environmentally efficient is the stone marketing and sales operation? Is the stone showroom a LEED-certified new construction or LEED-certified commercial interior? How is the stone delivered to the construction site?

Stone quarries exist throughout the U.S., so stone is normally a readily available local material. LEED guidelines suggest selecting local materials extracted and/or manufactured within a 500-mile radius of the building site. When transporting stone, locally energy-efficient diesel or natural gas-fueled trucks could have lower EE transportation costs. Stone coloration varies from area to area, so builders who want to adhere to the 500-mile guideline should consider coloration. And when importing stone, lower EE transportation costs by rail or container ship should be considered.

In addition to upstream-embodied energy costs, there are also downstream-embodied energy costs of material disposal. Over the lifecycle of a building, most building materials have to be renewed or substituted And disposed of; however, stone is so incredibly durable that new replacement stone doesn’t have to be installed for a long time. The average lifecycle of natural stone can range from 100 years or longer, while some ancient stone buildings have never really completely worn out. For example, there are Neolithic stone age temples still standing in Malta that are older than Stonehenge and even older than the great pyramids of Giza. Stone can be untimely salvaged and reused extending the lifecycle of the product. Reclaimed stone can be crushed or simply refinished and reused. Many of the renaissance churches built in Rome, for instance, were constructed from reclaimed stone from the ruins of the Roman Colosseum.

Taken together, the upstream and downstream- embodied energy of a structure’s building materials contributes anywhere from 15 to 20% of the energy used by a building over a 50-year period. Although the operating energy of a building during its use is the majority of energy consumed by a building, the embodied energy of building materials will become a greater percentage of the building energy use as buildings become more energy efficient.

THERMAL PERFORMANCE

Natural stone, during a building’s period of use, can improve thermal performance by reducing the heat island effect of higher air and surface temperatures associated with concrete paving. By using light-colored natural stone pavers with a solar-reflective index of 29 or greater, the highly solar reflective pavers can reduce the absorption, retention and emittance of solar heat thereby maintaining the solar heated temperatures of the pavers more than 20 degrees F cooler than the concrete paving.

Natural stone paving used for interior flooring in place of carpeting may contribute to exceptional performance in areas such as mold resistance and improved air quality. Their hard surfaces are easy to clean, so they don’t harbor the allergens and irritants that carpeting can trap. Also, it does not off-gas, so it’s good for indoor air quality, and it makes a good thermal heat sink. Natural stone has a high thermal mass, which is defined as the ability of a material to store heat and then slowly release it. In the architectural sense, it is the high mass interior stone walls that absorbs and stores heat during sunny periods When the heat is not desirable in the living space of a building, and then releases the heat during overcast periods or during the night, when the heat is desirable. The same can be said for not absorbing heat during hot periods of weather. The internal mass remains at a lower temperature than hot outside temperatures, keeping the occupants at a more comfortable interior temperature. Cooling the internal mass can then be achieved through ventilation at night. The amount of thermal mass in a non-conditioned structure typically determines the average diurnal temperature swing within the structure. Buildings with large areas of interior stone walls have a large interior thermal mass and will therefore have a much lower interior diurnal temperature swing.

Facades of natural stone and glazing excel with regard to energy efficiency when compared to all glass facades. The heat transfer coefficient for a facade of natural stone and glass is far below that of an all glass facade because of the lower heat conductivity of stone in comparison to glass. This results in lower heat losses in winter and lower air conditioning costs in summer. Likewise, the maintenance costs of natural stone facades amount to only half of the costs for maintaining glass facades.

A German study by Deutscher Naturwerkstein- Verbands (DNV) of Würzburg, Germany, shows that using natural stone rain screen facades rather than all glass facades can considerably reduce the environmental impact of building construction And use, and it can cost less overall. DNV looked at a new office building in Germany, the Opera Tower in Frankfurt, using a lifecycle assessment to compare the energy consumption per square meter of typical facade constructions of extensive glass facades with a substructure of aluminum and a natural stone and glass rain screen with insulation and concrete backing. The DNV study found that the glass and aluminum facade consumed as much as three times more primary energy in production and use than the stone and glass facade, and the total environmental effects of the glass over the whole lifecycle could be as much as 360% greater. The Bavarian Supreme Court of Audit came to the conclusion that the investment costs rise proportional to the amount of glass used in construction. Also, the maintenance costs of natural stone facades amount to only half of the costs for maintaining glass facades.

CREATING TIMELESS, SUSTAINABLE DESIGN

Beyond the environmental performance of natural stone, the classic beauty of stone products — their unique richness, grandeur and elegance — are powerful characteristics of stone as a sustainable building product. Good stone buildings have an essential timeless character that remains steadfast over the life of the building. For instance, the visual and sensory appeal of vernacular stone buildings is most often related to the history and the context of its regional environment. This vernacular architecture is categorized by methods of construction, which use local resources and traditions that reflect the environmental, cultural and historical context of a region. In Central Texas the regional vernacular architecture is typically stone building. The abundant limestone available in Central Texas was the primary building material of the late seventeenth and early eighteenth century Spanish missions in Texas. Spanish missionaries and colonists brought to Texas building types and construction techniques they had known at home in Spanish Baroque stone building traditions. The early limestone buildings were adapted to the climate of Central Texas and established the vernacular architecture found in ninetieth century German heritage towns like Gruene and Fredericksburg. These early vernacular designs have influenced a modern interpretation of vernacular stone building. Modern vernacular stone building reflects modern comfort, yet utilizing local materials, establishes an energy efficient response to the natural environment.

One of the foremost practitioners of modern vernacular stone building in Austin, TX, is the work of Black and Vernooy, FAIA. Their stone building designs embrace their sites, Reflecting their limestone hill country locations. They achieve a regional character through the abstraction of elements of Texas culture. Their designs celebrate the unique warm climatic conditions of Central Texas, facilitating natural ventilation, shading and the thermal mass tempering effect associated with stone building. Their sustainable building designs in stone reduce the amount of non-renewable energy resources required to achieve thermal comfort. The natural outdoor environment is brought into the interiors of their building design projects by connecting living areas to outdoor terraces covered with limestone pavers. Surrounding ramadas provide shading for terraces used for observing nature and their designs create a harmony with the natural landscape to produce a lasting sense of an environmentally conscious place.

Another Austin architectural design firm known for achieving a delicate balance in combining traditional stone vernacular building with a modern style is Mell Lawrence Architects. The design work of this firm honors the best of timeless building traditions while embracing modern building technologies and celebrating the extraordinary within the ordinary, seeking results that are timeless.

Making the most of the warmth and texture of natural elemental materials like Lueders limestone, their designs blend indoor and outdoor spaces with seamless transitions that acknowledge the elements of the surrounding landscape. Mell Lawrence describes his work as, “the celebration of the simplicity of elemental materials, the truth of nature, the inspiration of beauty, and The delight of the sun’s animating light.” The stone building design work of Black and Vernooy and Mell Lawrence amplifies that stone is both a timeless and beautiful modern building material choice.

Over and above its historical and aesthetic value, natural stone, by definition, is a sustainable building choice. Whether the building material is being specified to lessen the building’s carbon footprint, gain points towards green certification, or simply to choose a durable product that has a lighter impact on the environment, stone is a sustainable building material. Stone is a highly durable, low-maintenance material with a high thermal mass. It is versatile, available in many sizes, shapes, colors and finishes, and it can be used for floors, walls, lintels and arches as well as in landscaping. Stone blends well with the natural landscape, and it can easily be recycled for other building purposes. These attributes make stone building a popular sustainable choice in the green building industry.

Because we are in an era of diminishing domestic U.S. oil discoveries, and because of the forecast of future energy and environmental problems associated with increasing U.S. oil imports, green building has become an important development in the construction industry. Green building and energy efficiency can make a significant contribution to energy savings, so it has become an increasingly popular movement over the past decade. It is critical for the stone industry and members of the design community to become part of this movement and to document the energy and environmental cost savings of stone building on a whole lifecycle basis. The challenge for the building industry is to embrace green building; and for the stone building community, it is to create financially and environmentally sustainable buildings in stone which in every sense stand the test of time.

ABOUT THE AUTHOR: Michael Garrison, Professor, University of Texas School of Architecture, is currently active in the design and construction of sustainable buildings. He has served as the faculty sponsor of the 2002, 2005, and 2007 Solar Decathlon competitions administered by the U.S. Department of Energy. Garrison is currently principal investigator for a Zero Net Energy high-rise tower for Shreveport, LA, sponsored by Community Renewal International and his research has received numerous grants and awards. Professor Garrison is the author of a number of publications including Passive Solar Homes for Texas (1982) and Building Envelopes, with Randall Stout (NCARB 2004).