The Passivhaus Institut in Darmstadt, Germany, on Friday announced 20 finalists for its 2014 Passive House Awards, singling out houses, office buildings, and other structures designed and built to the institute's exacting standards. (Put simply, certified passive houses have airtight envelopes and require no artificial heating or cooling.) An international jury selected finalists in six categories—single-family houses;apartment buildings; office and special-use buildings; retrofits; and urban planning. Among them are three projects in the United States, where the Passive House concept has been slower to catch on than in Europe. The winners will be announced in Aachen, Germany, on April 25. Click through the slideshow to view a selection of the finalists.