A passive home is one that requires minimal heating and cooling. In essence these homes are very energy efficient reducing its ecological footprint. The "Passivhaus" concept was developed in Germany in the 1980's. It includes superior insulation, airtight construction, high performance windows, ventilation with heat recovery, elimination of thermal bridges or paths where eat can flow through the building, utilization of passive solar heating, energy efficient appliances and lighting, and monitoring that the building meets a standard. As a result, Passive Houses typically use up to 90% less energy for heating and cooling compared to conventional buildings. A particular architectural style is not necessarily prescribed. Passive houses can vary in design and appearance, just as long as they meet the criteria outlined for energy performance.