The environmental impacts of human activity have been a source of controversy and concern for many years. Much of the focus over that time has been on impacts such as pollution and the destruction or degradation of wildlife habitats and ecosystems. Over the past few decades, however, concerns have increased greatly about greenhouse gases, resource depletion, and degradation of ecological services such as water supply. Over that time, the impacts of buildings have come under increasing scrutiny. There are many different kinds of buildings—residential, commercial, government, and those with special uses such as schools and hospitals—and they form a large and core component of the nation's infrastructure. The construction, characteristics, operation, and demolition of buildings are now recognized as a major source of environmental impact, including direct effects on the humans who use them. U.S. buildings consume vast amounts of resources annually in the form of electricity for lighting and temperature control, drinkable water for indoor and outdoor use, and construction materials with diverse supply chains and manufacturing processes; they also produce substantial waste streams throughout their lifecycles, from construction to daily operations to demolition. Such resource use can impose high environmental and financial costs. For example, buildings account for about 40% of energy consumption in the United States, producing approximately 40% of anthropogenic greenhouse gas emissions, and costing consumers more than $430 billion a year in energy bills. A building's location and interaction with its surrounding environment also influences its ecological and human health impacts. Buildings create impermeable surfaces that can have substantial effects on stormwater management and associated health and environmental impacts. A building's proximity to public transportation affects the energy required to transport occupants to and from the premises. If an office is not accessible by walking or public transit, for example, occupants may need to commute by car, contributing to traffic delays, smog, and greenhouse gas emissions. Occupant health and productivity is also affected by building features that determine indoor air quality. Most people spend far more time indoors than outside, and the air in buildings often has substantially higher concentrations of pollutants than the air outside, contributing in extreme cases to a phenomenon known as "sick building syndrome." These and other undesirable environmental and health impacts can be addressed for construction, renovation, and operations of both new and existing buildings. Green building is a tool for transforming the ways in which buildings are designed, built, operated, and demolished that has generated substantial interest in recent decades. Since emerging as a relatively novel concept in the 1990s, green building has grown into what many consider a respected approach to building, with an increasing number of stakeholders. They include, among others, private construction firms, building owners and occupants, green building certification and standards-developing organizations, federal and state lawmakers, local code officials, and a variety of government agencies. This report discusses the concept of green building, major federal policies and programs relating to it, and associated issues. Topics covered include how green building is defined, what it consists of, the major areas of environmental impact it seeks to address, an overview of the tools available for ensuring that a building conforms to green criteria, outstanding issues in the implementation of green building, an overview of the major statutory and executive authorities that address it, and programs in federal agencies that involve one or more elements related to it. Environmentally sensitive building is not a particularly recent phenomenon, but the modern practice of green building began emerging in the 1990s. One milestone in the United States was the formation in 1990 of the Committee on the Environment within the American Institute of Architects (AIA), followed within a few years by the founding of the U.S. Green Building Council (USGBC) and other organizations. The most prominent federal green building project in that decade was the "Greening of the White House." From those beginnings, the concept of green building has expanded to encompass both the movement to promote environmentally conscious design principles and the set of practices and strategies by which builders seek to reduce harmful impacts of the built environment. There is no single consensus definition of green building; efforts exist along a design and performance continuum. What some call green building is barely distinguishable from standard building practices. At the extreme, the term can be used in an almost meaningless way, purely as a marketing tool. Such practices are sometimes called "greenwashing." In contrast, some practitioners aim to provide buildings with environmental impacts that are greatly reduced from those of typical buildings. Examples include the so-called "zero-impact" building, which is intended to have no net environmental impact, including but not limited to net-zero energy use; and the "minus-impact" building, which would provide a net environmental benefit (see " Net-Zero Buildings ," below). Most green building efforts have less ambitious reduction goals. In general, green building might best be characterized as an integrated approach to building design, construction, and operations that significantly reduces the environmental footprint of buildings in comparison to standard practices. The environmental footprint is the overall impact of a structure or activity on the environment, including the human environment. This characterization captures two common features of the various meanings given to the term. First, green is a relative concept—a green building is one that is greener than average. Second, it is not limited to only one factor, such as energy consumption, but involves integration across several, as is discussed below. The green building approach can be applied to any class of building: large or small, commercial or residential. Green builders seek to achieve improvements in environmental performance through a variety of techniques and strategies, from the implementation of innovative technologies (such as energy-efficient heating and cooling systems) to design features intended to influence occupant behavior (such as placing stairways prominently to encourage their use). Some of these techniques will be discussed in more detail below. Decisions about which of these techniques will be used are often made in the design and planning phase, but can impact the environmental footprint of a building throughout its lifecycle. As a result, green building techniques are most often applied to new construction, through there is a growing incidence of green renovation and retrofit projects. The term green building is often used interchangeably with others such as sustainable building , and that practice is followed in this report. However, the terms may also be used in ways that are not exactly synonymous. For example, sustainable building may be described as a form of green building, but with a more stringent goal of indefinitely maintaining environmental footprints that are small enough that they will not impede future human activity and the functioning of ecosystems. Another term often used interchangeably with green building is high-performance building. However, high-performance building usually involves other factors such as security in addition to environmental ones. There are two federal statutory definitions: a building that integrates and optimizes all major high-performance building attributes, including energy efficiency, durability, life-cycle performance, and occupant productivity, and a building that integrates and optimizes on a life cycle basis all major high performance attributes, including energy conservation, environment, safety, security, durability, accessibility, cost-benefit, productivity, sustainability, functionality, and operational considerations. Additional objectives may also be considered in the design of high-performance buildings, including aesthetics and historical preservation. The " Energy Independence and Security Act of 2007 " (EISA) further refined the concept by establishing a detailed definition for high-performance green buildings (see " Definitions of Green Building ," above). Descriptions of green building generally focus on specified elements, which in various documents may also be referred to by other terms such as attributes, life-cycle parameters, performance areas, or impact categories. Commonly cited elements are energy, water, materials, waste, and health. Another is siting, particularly with respect to transportation, ecology, and smart growth. The siting element has increased in prominence over the last several years as more attention has focused on the built environment beyond the building itself. Most descriptions do not explicitly include a serviceability, productivity, or functionality element, but that may be because those would be commonly expected to be integral elements of any building design. However, they are included explicitly among the objectives for high-performance buildings, which may also consider such others as disaster and climate resilience. These objectives have risen in prominence in the wake of a number of high-profile natural disasters, including Hurricanes Katrina and Sandy, and the 2011 earthquake and tsunami that initiated the Fukushima Daiichi nuclear meltdown. The goals of a given green building project may vary depending on the needs of the stakeholders, including a building's expected occupants. As a result, different elements may be prioritized in different projects (see " Net-Zero Buildings ," below). Local factors such as climate zone and flood risk may influence the design process in ways that affect the relative emphasis placed on the various elements discussed below. A reduced energy footprint is probably the most widely cited element of green building. Techniques include energy efficiency and conservation, through such means as energy-efficient appliances and lighting, weatherization, and daylighting; use of alternative, renewable sources of energy, such as solar or geothermal power or combustion of biomass; utilization of energy storage technologies, often in combination with on-site renewable energy generation; and participation in smart-grid innovations such as demand-response programs. Energy is widely considered a crucial element because of the economic costs and environmental impacts associated with energy use. A 2010 study by the National Academies found the potential energy savings from widespread deployment of energy efficiency measures to be significantly higher for buildings than for transportation and industry. In a 2015 report on energy technologies, the Department of Energy estimated that buildings using the best available energy efficiency technologies would consume about half as much energy on average as those in the current building stock. Federal law sets numeric requirements for reductions in energy use by federal buildings. The energy intensity of such buildings declined by more than 22% from 2003 to 2015. Nevertheless, 2015 consumption exceeded the federal goal. Given its importance, energy is sometimes mistakenly treated as the predominant or even the sole element to be considered in green building.