The advances in research and in building techniques achieved by the above-mentioned green design luminaries have been compiled into a reliable database of environmental construction methods and sustainable materials—some of which have been in use for thousands of years yet remain the basis for contemporary advances in environmental technology. For private residences of the 21st century, the essential green design principles are as follows:

• Alternative energy sources. Whenever feasible, build homes and communities that supply their own power; such buildings may operate entirely off the regional power grid, or they may be able to feed excess energy back onto the grid. Wind and solar power are the usual alternatives. The quality of solar collectors and photovoltaic panels continues to improve with the advance of technology; practical considerations for choosing one supplier over another include price, durability, availability, delivery method, technology, and warranty support.
• Energy conservation. Weatherize buildings for maximum protection against the loss of warm or cool air. Major chemical companies have developed responsibly manufactured, dependable, moisture-resistant insulating materials that do not cause indoor humidity problems. Laminated glass was also radically improved at the end of the 20th century; some windows provide the same insulation value as traditional stone, masonry, and wood construction. In regions that experience extreme heat, straw-bale or mud-brick construction—used since ancient times—is a good way to save money and energy.
• Reuse of materials. Use recycled building materials. Although such products were scarce in the early 1990s, since the early 21st century they have been readily available from a burgeoning number of companies that specialize in salvaging materials from demolition sites.
• Careful siting. Consider using underground or earth-sheltered architecture, which can be ideal for domestic living. Starting at a depth of about 1.5 metres (5 feet) below the surface, the temperature is a constant 52 °F (11 °C)—which makes the earth itself a dependable source of climate control.

Individual, corporate, and governmental efforts to comply with or enforce LEED or BREEAM standards include recycling at household and community levels, constructing smaller and more efficient buildings, and encouraging off-the-grid energy supplies. Such efforts alone cannot preserve the global ecosystem, however. On the most basic level, the ultimate success of any globally sanctioned environmental movement depends as much on its social, psychological, and aesthetic appeal as on its use of advanced technologies.

The environmental movement in the 21st century can succeed only to the extent that its proponents achieve a broad-based philosophical accord and provide the same kind of persuasive catalyst for change that the Industrial Revolution offered in the 19th century. This means shaping a truly global (as well as optimistic and persuasive) philosophy of the environment. Much depends on the building arts and integrative thinking. Architects will have to abandon 20th-century specialization and reliance on technology and, with builders and clients, help support grassroots, community-oriented, and globally unifying objectives. In the words of Earth Day founder Gaylord Nelson,

The ultimate test of man’s conscience may be his willingness to sacrifice something today for future generations whose words of thanks will not be heard.