A building needs to meet a long list of requirements relating to its air tightness, energy efficiency and construction standards before it can be considered a passive house. To be certified by the Passivhaus Institut in Darmstadt, Germany, a passive house must consume less than 15 kilowatt-hours of electricity per square meter per year for its heating and cooling, with total energy consumption for all heat, hot water and household electricity that doesn't exceed 120 kilowatt-hours per square meter per year [source: Passivhaus Institut].
In addition to awarding its "Quality Approved Passive House" certificate to qualifying homes, the Passivhaus Institut offers a "Certified Passive House Designer" certificate to individual architects, builders, engineers and others who pass an examination or complete an approved passive house construction project.
In a passive house, the building itself and its mechanical systems are treated as one single, overall system. To help maintain the necessary balance in the system between hot and cold, and between stale air and fresh, architects and engineers use a sophisticated software program to design passive homes and determine their projected energy usage. The software helps to determine everything from the optimal size and location of windows and the recommended capacity for the ventilation system, to suggestions for minimizing construction costs without compromising quality or efficiency.
Despite the high standards required for passive house certification, most conventional houses can be remodeled to achieve passive house status by making improvements to the insulation and air tightness, replacing existing windows with high-efficiency windows, and modifying the existing duct work to accommodate the passive house system of heat recovery from exhaust air [source: Feist].
So are passive houses worth the effort? By most estimates, all these stringent requirements, tests and certifications pay off in a big way: Passive homes provide an average energy savings of 90 percent over conventional homes and up to 80 percent compared to homes built to modern European standards for energy consumption [source: Passivhaus Institut].