Adobe: rediscovering an old energy saver

A home built with adobe-mud bricks dried in the sun radiates warmth in more ways than one. And that fact has added new glow to this ancient building material, used all over the world and gaining new popularity in some parts of the US Southwest.

In sunny climates, adobe walls -- because they are thick and massive -- can absorb daytime heat and slowly release it at night. That can give adobe structures an energy advantage over homes built with conventional materials in reducing heating bills, particularly in desert regions where there is a wide difference between day and night temperatures.

Just as important to adobe devotees is the natural, soft-edged beauty of mud structures. "It's an art form. You can shape it and mold it to your taste," says P. G. McHenry, an adobe-home builder in Albuquerque.

"It has a very cozy feel," agrees Abel Davis, a retiree from Chicago now living in an adobe home just outside of Santa Fe.

Mr. McHenry estimates that the number of new adobe home being built annually in the Albuquerque area, though less than 10 percent of the entire new home market, has tripled in the past 10 years.Adobe is also used in west Texas, southern Arizona, and southern California. Its use is basically confined to areas without heavy rainfall, which can erode the earthen structures.

In Santa Fe, adobe has become so popular that nearly everything is built in that style, although most new buildings are not really made of mud.

Older authentic adobe houses in Santa Fe are at a premium. "Anglos moving to the area are tired of the suburbs so they look for adobes. For the Hispanics and Indians adobe is a symbol of poverty, so they are eager to move out to the suburbs," says Santa Fe architect William Haney. The result is that used adobe homes are selling for highly inflated prices, he says.

Because making mud bricks requires a lot of manual labor, and they are a slow material to build with, new adobe homes are also expensive.

Dirt, with the proper amount of clay, silt, and sand, is mixed with water in a large pit either by hand or with a tractor. It is poured into wooden molds and dried for a week or longer in the sun.

The bricks are mortared with mud and plastered over to form 10- to 12-inch thick walls. Standard walls are usually less than half that thickness. (Old adobe structures have walls several feet thick.)

New adobe homes in New Mexico typically sell for $100,000 or more, and are usually custom designed and built. Tract adobes are virtually nonexistent.

Adobe's natural property as a good temperature conduit makes it a popular material for use in passive solar homes. Interior walls made of adobe, for example, can effectively absorb and slowly release solar heat in homes with lots of windows.

Susan Nichols, president of Communico, a Santa Fe residential building firm, says her firm uses interior adobe walls in many of the solar-designed houses it builds, even though the exteriors are made of conventional materials like wood or cement.

One drawback to adobe is that it is not a good insulator -- a property that is increasingly important in the housing construction industry. Most builders prefer materials that are highly resistant to heat transfer.

The Department of Housing and Urban Development has stopped using adobe in the construction of Indian housing in northern New Mexico because it does not meet current federal building standards for insulating ability.

Mr. Haney has been asked by the Indian Pueblos Council of Northern New Mexico to study the overall energy efficiency of adobe. "Federal building codes talk only about heat resistance. But adobe operates on a different basis where the ability to absorb heat is an advantage," Mr. Haney says.