Passive House is a building concept based on rigorous energy performance and comfort principles. Side by side you may not be able to tell a passive house building from another, they may look the same but a passive house building will perform much better. With passive house it is in the details you don't see.
According to Passive House Institute U.S a passive building is built according to these five building standards.
• Employs continuous insulation throughout its entire envelope without any thermal bridging.
• The building envelope is extremely airtight, preventing infiltration of outside air and loss of conditioned air.
• Employs high-performance windows and doors - solar gain is managed to exploit the sun's energy in the heating season and to minimize overheating during the cooling season.
• Uses some form of balanced heat and moisture recovery ventilation.
• Uses a minimal space conditioning system.
Phius.org / what is passive building / passive house principles
Warren Construction has built two passive house buildings recently, The Friends School of Portland and the Maine Coast Waldorf High School. You can read more about the surge of passive house building in Maine here.