The current Building Act was passed in 2004 and it requires the efficient use of energy, including new principles to drive energy conservation and facilitate the use of renewable energy.New buildings are required to be designed, constructed and able to be used in ways that promote sustainable development. In response to the 2004 Act, a major review of the Building Code began in 2004, including a complete review of the energy efficiency requirements of the current Code and future energy needs. During 2004, the Energy Efficiency and Conservation Authority (EECA) and the Department of Building and Housing worked to further enhance energy in the Building Code.The thermal properties of windows are now included in the Code for residential buildings so that most new residential construction in the cooler parts of the country are double-glazed. Various technical research reports have been completed to underpin the major review of the energy requirements of the New Zealand Building Code.To further improve the energy performance of residential buildings, the New Zealand Government amended the Building Code in 2007/08 so new homes require more insulation (in ceilings, walls and floors) and double glazed windows. These requirements apply to all new houses, major extensions to existing houses, to new multi-unit residential apartments, and to new small buildings with a floor area up to 300 square meters (e.g. small shops). It is estimated that houses built to the new Code requirements consume about 30% less energy than houses built to the old Code requirements.