Older houses also can also be renovated to meet passive-house standards, but such renovations are rare because of the extra-thick walls and high technological requirements that certified passive houses demand.
Building new passive houses and renovating existing buildings to passive-house standards are tiny steps in Germany's daunting challenge to cut energy consumption as it seeks to replace nuclear power with renewable energy.
For the spy with a yen to be green, the house has low utility bills courtesy of a passive solar design, low-E windows and solar-generated water heater.