What is Sustainability
Sustainability is the capacity to endure. In ecology the word describes how biological systems remain diverse and productive over time. For humans it is the potential for long-term maintenance of wellbeing, which in turn depends on the wellbeing of the natural world and the responsible use of natural resources.
Sustainability has become a wide-ranging term that can be applied to almost every facet of life on Earth, from local to a global scale and over various time periods. Long-lived and healthy wetlands and forests are examples of sustainable biological systems. Invisible chemical cycles redistribute water, oxygen, nitrogen and carbon through the world's living and non-living systems, and have sustained life for millions of years. As the earth’s human population has increased, natural ecosystems have declined and changes in the balance of natural cycles has had a negative impact on both humans and other living systems.
According to the Earth Policy Institute, there is abundant scientific evidence that humanity is living unsustainably, and returning human use of natural resources to within sustainable limits will require a major collective effort. Ways of living more sustainably can take many forms from reorganising living conditions (e.g., ecovillages, eco-municipalities and sustainable cities), reappraising economic sectors (permaculture, green building, sustainable agriculture), or work practices (sustainable architecture), using science to develop new technologies (green technologies, renewable energy), to adjustments in individual lifestyles that conserve natural resources.
Sustainable Design [cited from Wikipedia]
Sustainable design (also called environmental design, environmentally sustainable design, environmentally-conscious design, etc) is the philosophy of designing physical objects, the built environment and services to comply with the principles of economic, social, and ecological sustainability.
The intention of sustainable design is to "eliminate negative environmental impact completely through skillful, sensitive design". Manifestations of sustainable designs require no non-renewable resources, impact on the environment minimally, and relate people with the natural environment.
Applications of this philosophy range from the microcosm — small objects for everyday use, through to the macrocosm — buildings, cities, and the earth's physical surface. It is a philosophy that can be applied in the fields of architecture, landscape architecture, urban design, urban planning, engineering, graphic design, industrial design, interior design, and fashion design.
Sustainable design is mostly a general reaction to global environmental crises, the rapid growth of economic activity and human population, depletion of natural resources, damage to ecosystems and loss of biodiversity.
The limits of sustainable design are reducing. Whole earth impacts are beginning to be considered because growth in goods and services is consistently outpacing gains in efficiency. As a result, the net effect of sustainable design to date has been to simply improve the efficiency of rapidly increasing impacts. The present approach, which focuses on the efficiency of delivering individual goods and services does not solve this problem. The basic dilemmas include: the increasing complexity of efficiency improvements, the difficulty of implementing new technologies in societies built around old ones, that physical impacts of delivering goods and services are not localized but distributed throughout the economies, and that the scale of resource uses is growing and not stabilizing.
Principles of sustainable design
While the practical application varies among disciplines, some common principles are as follows:
Low-impact materials: choose non-toxic, sustainably-produced or recycled materials which require little energy to process
Energy efficiency: use manufacturing processes and produce products which require less energy
Quality and durability: longer-lasting and better-functioning products will have to be replaced less frequently, reducing the impacts of producing replacements
Design for reuse and recycling: "Products, processes, and systems should be designed for performance in a commercial 'afterlife'."
Design Impact Measures for total carbon footprint and life-cycle assessment for any resource use are increasingly required and available. Many are complex, but some give a quick and accurate whole earth estimates of impacts. One is estimating any spending as consuming an average economic share of global energy use as 8000btu/$ and CO2 production of .57kgCO2/$ (1995$) from DOE figures.
Sustainable Design Standards and project design guides are also increasingly available and are vigorously being developed by a wide array of private organizations and individuals. There is also a large body of new methods emerging from the rapid development of what has become known as 'sustainability science' promoted by a wide variety of educational and governmental institutions.
Biomimicry: "redesigning industrial systems on biological lines ... enabling the constant reuse of materials in continuous closed cycles..."
Service substitution: shifting the mode of consumption from personal ownership of products to provision of services which provide similar functions, e.g. from a private automobile to a carsharing service. Such a system promotes minimal resource use per unit of consumption (e.g., per trip driven).
Renewability: materials should come from nearby (local or bioregional), sustainably-managed renewable sources that can be composted when their usefulness has been exhausted.
Healthy Buildings: sustainable building design aims to create buildings that are not harmful to their occupants nor to the larger environment. An important emphasis is on indoor environmental quality, especially indoor air quality. 
Renewable Resource [cited from Wikipedia]
A natural resource is a renewable resource if it is replaced by natural processes at a rate comparable or faster than its rate of consumption by humans. Solar radiation, tides, winds and hydroelectricity are perpetual resources that are in no danger of a lack of long-term availability. Renewable resources may also mean commodities such as wood, paper, and leather, if harvesting is performed in a sustainable manner.
Some natural renewable resources such as geothermal power, fresh water, timber, and biomass must be carefully managed to avoid exceeding the world's capacity to replenish them. A life cycle assessment provides a systematic means of evaluating renewability.
The term has a connotation of sustainability of the natural environment. Gasoline, coal, natural gas, diesel, and other commodities derived from fossil fuels are non-renewable. Unlike fossil fuels, a renewable resource can have a sustainable yield.