further states that, "where BREEAM is used, all new projects are to achieve an 'excellent' rating and all refurbishment projects are to achieve at least 'very good' rating." United States In 1998, the US Green Building Council devised its own building certification system through the Leadership in Energy and Environmental Design (LEED) certification. It has its own set of criteria for assessment and utilizes the ASHRAE codes and standards. Due to its simplicity and ease-of-use, the LEED quickly gained international recognition within a short period. Over the years, LEED has undergone many changes and is now currently in its fourth iteration, which was launched in late 2013. LEED rating systems differ according to the type of the project. The different types of rating systems fall under: Building Design and Construction: For new construction or major renovations Interior Design and Construction: For commercial interior fit-out projects Building Operations and Maintenance: For existing buildings undergoing improvement but with little construction work Neighborhood Development: For new land development projects or redevelopment projects Homes: For single family, low-rise multi-family or mid-rise multi-family homes Cities and Communities: For entire cities or sub-sections of a city. Assessment of a city's water consumption, energy use, waste, transportation etc. LEED Recertification: For occupied and currently-in-use projects that have already received LEED certification but aiming to maintain and improve the building. LEED Zero: For projects with net-zero goals in carbon emissions and resource use. LEED certification is voluntary and a qualified assessor evaluates the projects on the basis of various established categories. These categories are as follows: Integrative process Location and transportation Sustainable sites Water efficiency Energy and atmosphere Materials and resources Indoor environmental quality Innovation in design Regional priority The four levels of LEED certification are: Platinum, Gold, Silver and Certified. References Sustainable energy Sustainable technologies Energy efficiency Low-energy building Sustainable architecture