Engineering and Construction

In the United States, the most widely adopted method for rating the environmental sustainability of a building’s design and construction is the  U.S. Green Building Council’s Leadership in Energy and Environmental Design, or  LEED™,  rating system. LEED for New Construction and Major Renovation projects, termed LEED-NC, groups sustainability goals into categories including site selection and development, effi  ciency  in water use, reductions in energy consumption and in the production of atmospheric ozone-depleting gases, minimizing construction waste and the depletion of nonrenewable resources, improving the quality of the indoor environment, and encouraging innovation in sustainable design and construction practices (Figure 1.1).

Within each category are specifi  c credits that contribute points toward a  building’s overall assessment of sustainability. Depending on the total  number of points accumulated, four  levels of sustainable design are recognized, including, in order of increasing performance, Certifi  ed,  Silver, Gold, and Platinum.

Figure 1.1 The LEED-NC 2009 Project Scorecard.  The document shown here was in draft status at the time of this publication.  See the U.S. Green Building Council web site for the most current version of this document.

The process of achieving LEED certifi  cation for a proposed new building begins at the earliest stages of project conception, continues throughout the design and construction of the project, and involves the combined ef-forts of the owner, designer, and builder. During this process, the successful achievement of individual credits is documented and submitted to the Green Building Council, which then  makes the fi  nal  certifi  cation of the  project’s LEED compliance.

The U.S. Green Building Council continues to refi ne and improve upon LEED-NC and is expanding its
family of rating systems to include existing buildings (LEED-EB), commercial interiors (LEED-CI), build-
ing core and shell construction (LEED-CS), homes (LEED-H), and other categories of construction and
development. Through international sister organizations, LEED is being implemented in Canada and other countries. Other green building programs, such as the Green Building Initiative’s  Green Globes, the Na-
tional Association of Home Builders’ Green Home Building Guidelines, and the International Code Council and National Association of Home Builders’ jointly developed National Green Building Standard, offer alternative as-sessment schemes.

Some green building efforts focus more narrowly on reducing building energy consumption, a measure of building performance that frequently correlates closely with the generation of greenhouse gas emissions and global warming trends. The American Society of  Heating, Refrigerating and Air-Con-ditioning Engineers’ Advanced Energy Design Guides and the U.S. Environmental Protection Agency’s  Energy Star program both set goals for reductions in energy consumption in new buildings that exceed current national standards.

These standards can be applied either as stand-alone programs or as part of a more comprehensive effort to achieve certification through LEED or some other green building assessment program.

Buildings can also be designed with the goal of zero energy use or carbon neutrality. A  net zero energy
building is one that consumes no more energy than it produces, usually when measured on an annual basis to account for seasonal differences in building energy consumption and on-site energy production. Net zero
energy use can be achieved using current technology combining on-site renewable energy generation (such as wind or solar power), passive heating and cooling strategies, a thermally efficient building enclosure, and highly efficient mechanical systems and appliances.

A  carbon-neutral  building is one that causes no net increase in the emission of carbon dioxide, the most
prevalent atmospheric greenhouse gas. If emissions due only to building operation are considered, the calcu-
lation is similar to that for a net zero energy building. If, however, the embodied carbon in the building’s full
life cycle—from materials extraction and manufacturing, through building construction and operations, to demolition, disposal, and recycling—is considered, the calculation becomes more complex. Carbon-neutral calculations may also consider the site on which the building resides. For example, what is the carbon footprint of a fully developed building site, including both its buildings and unbuilt areas, in comparison to that of the site prior to construction or in comparison to its natural state prior to human development of any kind?

Another possible consideration is, what role, if any,  should carbon offsetting (funding of offsite activities that reduce global carbon emissions, such as planting of trees), play in such calculations? Questions
such as these and the concepts of sustainability and how they relate to building construction will continue to evolve for the foreseeable future.

In addition, a sidebar in nearly every chapter describes the major issues of sustainability related to the materials and methods discussed in that chapter. These will be helpful in weighing the environmental costs of one material against those of another, and in learning how to build in such a way that we preserve for future generations the ability to meet their building needs in a reasonable and economical manner.

For more information on organizations whose mission is to raise our awareness and provide the knowl-
edge that we need to build sustainably, see the references listed at the end of this chapter.