Though the words “green” and “sustainable” are often used interchangeably, there are several differences between them, meaning that a “green” building is not always “sustainable.”
A building is green when it helps reduce the footprint it leaves on the natural environment and on the health of its inhabitants.
Green home design includes building for energy efficiency, including the use of renewable energy sources such as wind, water, or solar; creating a healthy indoor environment; implementing natural ventilation systems; and using construction materials that minimise the use of volatile organic compounds (VOCs) in the home.
The use of materials and resources that are sustainable, have low embodied energy, and produce a minimal environmental impact are key elements in green construction, as is the efficient use of water by appliances, faucets and shower heads, the recycling of grey water, and the reuse of rain water for landscaping and other non-potable purposes.
While the definition of green is relatively simple, sustainability has a more precise meaning derived from the term “sustainable agriculture,” which is the production of any plant or animal products using farming techniques that protect the environment, public health, human communities, and animal welfare without compromising future generations' ability to do the same.
According to the United States Environmental Protection Agency, sustainability “creates and maintains the conditions under which humans and nature can exist in productive harmony, that permit fulfilling the social, economic and other requirements of present and future generations.”
The importance of sustainability lies in the “future” factors, which set a higher standard than those used to define green building.
Sustainable products reduce the impact on the environment by using responsibly-sourced products; those that are either completely renewable or sustainably harvested. A sustainably harvested source material is gathered in a way that does not affect the surrounding area, pollute the air or permanently reduce the supply.
In ecology, the word “sustainable” describes how biological systems remain diverse and productive over time. For humans, it describes the potential for long-term maintenance of well-being, which in turn depends on the well-being of the natural world and the responsible use of natural resources
A very clear example of the difference between “green” and “sustainable,” can be the popular “green” bamboo flooring. There is no doubt that a lumber product made from a renewable resource is green, but most bamboo flooring is made in China and transported by ships and trucks to different countries all around the world. The air pollution caused and the fuel used to transport the material turn it into the opposite of a sustainable material, since it contributes to global climate change.
Another example can be the wood used to build a house. While wood is generally considered an eco-friendly or green product because it is natural and durable, it is not always sustainable. Wood is sustainable if the company that cuts down the trees does not permanently deplete the forest. If it is harvested in an environmentally irresponsible way, it is not sustainable at all.
Following this reasoning, it is very important to evaluate the way materials are produced and transported. Using reclaimed wood or FSC Controlled wood, can be both “green” and “sustainable.”
Only a house that meets zero energy standards - with zero net energy consumption and zero carbon emissions - can be considered sustainable. Buildings that contribute to urban sprawl and large homes which consume high levels of energy and resources can not be considered sustainable.
Architect Robert Stern, Dean of the Yale School of Architecture, noted that "in ten years we are not going to talk about sustainability anymore, because it is going to be built into the core processes of architecture."
With its growth in the architecture industry, claiming a building is sustainable will eventually be like an architect getting up in front of an audience to "proudly proclaim how his buildings did not fall down."