By ELISABETH ROSENTHAL


DARMSTADT, Germany - From the outside, there is nothing unusual about the stylish new gray and orange row houses in the Kranichstein District. But they are part of a revolution in building design: There are no drafts, no cold tile floors, no snuggling under blankets until the furnace kicks in. There is, in fact, no furnace.


In Berthold Kaufmann’s home, there is, to be fair, one radiator for emergency backup in the living room? but it is not in use. Even on the coldest nights in central Germany, Mr.Kaufmann’s new“passive house”and others of this design get all the heat and hot water they need from the amount of energy that would be needed to run a hair dryer.


“You don’t think about temperature? the house just adjusts,”said Mr. Kaufmann, watching his 2-year-old daughter, dressed in a Tshirt, eat a sausage in the spacious living room, whose glass doors open to a patio. His new home uses about one-twentieth the heating energy of his parents’home of roughly the same size, he said.


Architects in many countries, in attempts to meet new energy efficiency standards like the Leadership in Environmental and Energy Design standard in the United States, are designing homes with better insulation and high-efficiency appliances, as well as tapping into alternative sources of power, like solar panels and wind turbines.


The concept of the passive house, pioneered in this city of 140,000 outside Frankfurt, approaches the challenge from a different angle. Using ultrathick insulation and complex doors and windows, the architect engineers a home encased in an airtight shell, so that barely any heat escapes and barely any cold seeps in. That means a passive house can be warmed not only by the sun, but also by the heat from appliances and even from occupants’bodies.


And in Germany, passive houses cost only about 5 to 7 percent more to build than conventional houses.


Decades ago, attempts at creating sealed solar-heated homes failed, because of stagnant air and mold. But new passive houses use an ingenious central ventilation system. The warm air going out passes side by side with clean, cold air coming in, exchanging heat with 90 percent efficiency.


“The myth before was that to be warm you had to have heating. Our goal is to create a warm house without energy demand,”said Wolfgang Hasper, an engineer at the Passivhaus Institut in Darmstadt.“This is not about wearing thick pullovers, turning the thermostat down and putting up with drafts. It’s about being comfortable with less energy input, and we do this by recycling heating.”


There are now an estimated 15,000 passive houses around the world, the vast majority built in the past few years in German-speaking countries or Scandinavia.


The first passive home was built here in 1991 by Wolfgang Feist, a local physicist, but diffusion of the idea was slowed by language. The courses and literature were mostly in German, and even now the components are mass-produced only in this part of the world.


The industry is thriving in Germany, however? schools in Frankfurt are built with the technique.


Moreover, its popularity is spreading. The European Commission is promoting passive-house building, and the European Parliament has proposed that new buildings meet passive- house standards by 2011. The United States Army, long a presence in this part of Germany, is considering passive-house barracks.


“Awareness is skyrocketing; it’s hard for us to keep up with requests,”Mr.Hasper said.


Georg W.Zielke, who built his first passive house here, for his family, in 2003, said,“I grew up in a great old house that was always 10 degrees too cold, so I knew I wanted to make something different.”


Most passive houses allow about 45 square meters per person, a comfortable though not expansive living space. Mr.Hasper said people who wanted much larger houses should look for another design.


“Anyone who feels they need that much space to live,” he said, “well, that’s a different discussion.”