A passive house is a highly efficient building (residential or otherwise) that “passively” uses solar heat (sunshine) to drastically reduce the need for “active” heating and cooling, such as from an air conditioner and heating system.
Passive houses are able to do without central heating systems. Increasingly, old buildings can also be renovated to fulfill the standard. In warmer climates, passive houses can also be built largely to offset cooling demand.
Passive houses allow you to completely do away with heating systems even in a cold climate like Germany’s. Heating expenses are cut by an estimated 90 percent compared to a conventional new building, partly because backup heating systems can be so much smaller.
Passive houses are a combination of high-tech and low-tech. The low-tech aspect is relatively straightforward: homes are built facing the south in Germany. The southern façades have large glazed surfaces to allow a lot of sunlight and solar heat in during the cold season. In the summer, overhanging balconies on the south side provide shading, thereby preventing overheating, as do deciduous trees planted on the south side of the building, which provide additional shade in the summer but lose their leaves in the winter to let the sunlight pass through.
The high-tech aspects mainly concern the triple-glazed windows, which allow light and heat to enter but largely prevent heat from exiting the building. Most importantly, passive houses have ventilation systems with heat recovery, which also help prevent mold.
There are also many other types of efficient building strategies including zero-energy and plus-energy homes. Germans who renovate their homes to use less energy receive help from the government to do so.