The concept of ‘Passive Houses’ has been gaining some currency recently. On first glance it doesn’t sound terribly exciting. From this article in the Portland Daily Journal of Commerce, however, you can see that creating a passive house requires homeowners to take a number of active steps towards building or renovating a house that requires very little energy for heating or cooling. Apparently, the benchmark of a passive home is one where less than 15 watts per square foot is used to heat and cool the house during the entire year.

Most of the world's Passive Houses are located in Germany or Scandinavia

If you need more information on Passive Houses. Or as the Germans, who invented the concept, call them (PassivHaus), there’s always Wikipedia.