What is meant by a passive property?

This is a term used to describe buildings with ultra-low energy consumption that are playing an exceptional part in reducing their ecological footprint. These buildings require very little energy for either space heating or cooling.

Are there many passive properties?

In 2008, it was estimated that there were between 15,000 and 20,000 structures in Europe. In 2010, this had risen to approximately 25,000. In the US, in sharp contrast, there were only a handful, although construction is becoming more commonplace. The vast majority of passive structures have been built in German-speaking countries and Scandinavia.