11.2 Sustainability and buildings  (Page 2/10)

What is meant by a sustainable or green building? The U.S. EPA defines green building as “the practice of creating structures and using processes that are environmentally responsible and resource-efficient throughout a building's life-cycle from siting to design, construction, operation, maintenance, renovation and deconstruction. This practice expands and complements the classical building design concerns of economy, utility, durability, and comfort.” ( U.S. Environmental Protection Agency, 2010 )

The benefits of sustainable buildings have already been documented. These buildings can reduce energy use by 24-50%, carbon dioxide emissions by 33-39%, water use by 40%, and solid waste by 70% ( Turner&Frankel, 2008 ; Kats, Alevantis, Berman, Mills,&Perlman, 2003 ; Fowler&Rauch, 2008 ). Green building occupants are healthier and more productive than their counterparts in other buildings, and this is important because in the U.S, people spend an average of 90% or more of their time indoors ( U.S. Environmental Protection Agency, 1987 ). Green buildings tend to have improved indoor air quality and lighting.

There are also numerous perceived business benefits to green buildings, including decreased operating costs and increased building value, return on investment, occupancy ratio, and rent ratio.

Materials and methods of construction

It is frequently stated that the most sustainable building is the one that is not built. This does not mean that we should not have buildings, but rather that we should make the most of our existing buildings. Those buildings already have the infrastructure and have utilized many materials for their construction.

A great deal of energy goes into making building materials. By volume, the major materials used within the U.S. construction industry are crushed rock, gravel, sand, cement, cement concrete, asphalt concrete, timber products, clay brick, concrete block, drywall, roofing materials, steel, aluminum, copper and other metals, plastics, paper, paints, glues, and other chemical products. The building industry has been the largest consumer of materials in the US for nearly 100 years ( Horvath, 2004 ).

The manufacturing of cement, for instance, is an enormous producer of greenhouse gas emissions. Cement is made of about 85% lime by mass, which is mixed with other ingredients such as shale, clay, and slate. It is formed into an inorganic adhesive by heating the ingredients to a temperature of 1450 °C (2640 °F), and then grinding the product into a powder. Cement comprises about 15% of concrete, which is made by mixing cement with sand, small rocks, and water. Because it requires so much energy, the manufacture of cement is estimated to account for as much as 5% of global anthropogenic greenhouse gas emissions ( Humphreys&Mahasenan, 2002 ).

Construction of buildings is also related to deforestation. Our consumption of wood to build buildings and furniture over the centuries has resulted in the clearing of many old-world forests and tropical forests. Trees are harvested not only for fuel but also for construction material and to clear land for construction.