The Passivhaus Institut in Darnstadt, Germany, announced today that a million square meters of interior space—or nearly 10.8 million square feet—have been certified as having met the passive house standard. The threshold was crossed with the certification of a renovated Arts and Crafts-style house in Santa Cruz, California, dating to 1922, the institute reported. Passive houses are “zero-energy” structures that have no active heating or cooling systems and maintain a comfortable interior temperature through a combination of an airtight envelope and a heat-exchange system. “The primary purpose of certification is quality assurance,” says Zeno Bastian, head of building certification for the Passivhaus Institut. “With this internationally recognized seal, building owners are safe in the knowledge that the desired savings for heating costs and added benefits of a passive house will actually be realized.” Click through the slideshow for images of structures that the Passivhaus Institut named as finalists and winners of its 2014 Passive House Awards.