In a lot of places, the dirt often “cracks horrendously,” said Bill Steen, a natural builder in Elgin, Ariz., because “they just pound it into place.” Mr. Steen and his wife, Athena Swentzell Steen, have led an effort to modernize the techniques, adding sand and fiber in carefully calibrated amounts to control cracking.

Mr. Steen, 59, is half Mexican and grew up in an adobe house in Tucson with earthen patios. Ms. Swentzell Steen, 45, who is half Pueblo Indian, grew up in adobe houses in Santa Fe., N.M. “When you grow up and you’re living in a house that’s got three-foot adobe walls, that stuff just imprints on you.” Mr. Steen said.

“We kept thinking about the materials, the clay,” he added. “We decided to refine that recipe and make a floor that was crack-free, solid and really serviceable.” (Mr. Steen’s instructional pamphlet, “Earthen Floors,” is something of a bible to natural builders; it is out of print, but he said an updated version would be available on the couple’s Web site, caneloproject.com, within a few months.)

“There’s all sorts of recipes” for the floors, Mr. Steen said. “There’s no one way to do it.”

In fact, no firm standards seem to exist. Michelle Moore, a vice president of the United States Green Building Council, a nonprofit industry group in Washington that sets standards for pro-environment construction, said that its guidelines don’t even mention earthen floors or natural building. She said, however: “We envision a future where all buildings are green. Natural building techniques are an important part of that, but they’re not the only approach.”

And Steven Moore, director of the graduate program in sustainable design in the architecture school of the University of Texas at Austin, said that such building techniques “are not part of the program at all.”

For natural builders, the most practical benefit of earthen floors is thermal. (The high density and low thermal conductivity of an earthen floor allows it to capture and retain warmth.) Some builders install radiant heating systems in their floors, which circulate hot water and reduce the need for conventional heating. And when the floor receives direct sunlight it can act as a passive solar device, absorbing heat during the day and releasing it at night.

At the moment, the floors are more popular in the West than elsewhere. “The East Coast tends to be much more conservative,” said Mary Golden, a builder in Rochester who has contracts to install two earthen floors this summer and already has one in her own home. “And it’s inertia. They came out of the Southwest, and they’re taking their time moving across the country.”