To make things more complicated, no two passive houses are likely to be built to exactly the same specifications. Thousands of variables, including the architectural design, the size of the house, how many people will live there, and longitude and latitude, are taken into consideration by the sophisticated software created by Dr. Feist and his Passivhaus Institute in Darmstadt, Germany.

The first time Mr. Freas’s design team tried the computer modeling, it took them 100 hours. Now they have it down to 6.

And that’s before the real work begins. During construction, special fog machines and infrared cameras are often brought in to detect the smallest air leaks. Special tapes, gaskets and sealants are used on the wall seams to ensure they won’t break down over time and result in drafts.

And the more extreme the weather, the more insulation is needed. In a place as cold as Minnesota, a passive home’s walls would have to be 18 inches thick, but even in the more temperate Portland, Ore., 12 to 14 inches is typical.

This kind of meticulous construction results in big energy savings, but just how much is a matter of some dispute. Passive House advocates claim their buildings require 10 to 35 percent as much energy as standard buildings, while others, like Mr. Holladay, put that at closer to 50 percent.

Either way, getting it right is tricky, which is why 32 builders, architects and consultants recently gathered for a four-day training session in Seattle run by the Passive House Institute United States, which is based in Urbana. Many had beginners’ horror stories. One representative of Habitat for Humanity in Washington State introduced himself by saying, “I’m here because the passive house we built failed, and I need to understand what went wrong so it never happens again.”

Katrin Klingenberg, 44, the German-born architect who leads the institute, has been at the forefront of the American movement. As far as she is concerned, “Washington and Oregon are a piece of cake for passive house design,” she said.