Still voluntary in Europe--new buildings can be built with no or very low (one puny little 1000 watt electric heater?) heating other than passive--and this was in a house built in Illinois--significantly colder than most of Germany.
Primarily using superinsulation.
Handful of links:
The third one is a report on an Illinois house that was built to those standards (the place has supplementary heat--a thousand watt electric heater (fast loading .pdf file):
http://www.passiv.de/
http://en.wikipedia.org/wiki/Passive_house
http://www.naima.org/pages/resources/library/pdf/RP064.PDF
Thanks for that link Amanda:
The Energy Design Update article (http://www.naima.org/pages/resources/library/pdf/RP064.PDF) is worth printing out. The most interesting thing to me about the house was using I-joist for wall studs to allow for 12" of insulation. Trusjoist has a pdf of the building details (http://www.trusjoist.com/PDFFiles/GE-R05.pdf) but they are only in German!!
Here is a detail that will help to visualize the construction.
(https://i56.photobucket.com/albums/g166/jraabe/tji.jpg)
In addition the house has 14" of foam insulation under the slab!!! The general guidelines for this superinsulated passive solar augmented house (built in a Chicago area climate) was that all 6 sides of the house have at least an R-56 insulation level! When you get to that level your heating requirements are very low and a simple electric space heater is all that is needed. That or bring in a couple of dogs! :)
Follow-up: Even the homeowner and the German master of the system decided the insulation on this house was overdone. That said, it does have a great HRV that takes care of fresh air venting as well and heating and cooling (via earth tubes) - a German unit that is less expensive than the forced air furnace it replaces.
I just clicked on one of the Google ads and found this:
http://www.leonardo-energy.org/drupal/home_of_the_future
got lots of (you must have a ticket but the tickets are free type of) "Webinars" on various topics involving PassivHaus concepts.
don't know why the ad isn't above this topic.