Would you live in a house made of dirt?

The answer, I'm guessing, is no. As a building material, dirt has an image problem. Mud dwellings are practically synonymous with third-world poverty. At best, an earth structure is something you expect to encounter in an old hippie compound. Yet some of the world's most magnificent structures are made of little more than dirt and water, from New Mexico's pueblos to the great Djinguereber mosque in Timbuktu.

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Now, thanks to the effort of several committed architects, dirt is making a comeback, this time as the material of choice for modern buildings, including multistory ones.

Dirt's great advantage is that it's everywhere, making it the greenest building material you can use. Unlike conventional bricks, compressed mud blocks don't need to be fired. When packed into large wood forms and dried, in a process called rammed earth construction, dirt can have the same strength as concrete. Rammed earth walls keep out the cold in winter and the heat in summer. Dried earth smells nice - think springtime - and naturally regulates humidity. In the right hands, a mud building can be as gorgeous as anything imagined by Frank Lloyd Wright or Le Corbusier, two big-name architects who experimented with earth construction.

I knew nothing about dirt until I met Anna Heringer, a German architect who won a prestigious Aga Khan award in 2007 for designing a mud school in rural Bangladesh that fused the local building techniques with modern aesthetics. Bangladeshis have been abandoning mud in favor of costly imported materials and energy-intensive oven-baked bricks, but the success of Heringer's school, featured in a 2010 MoMA exhibition in New York, helped people see the old methods in a new light.

Like me, Heringer is a Loeb Fellow this year at Harvard's Graduate School of Design. She talked so much about the wonders of rammed earth structures that finally someone in our fellowship group said, Why don't we build one at Harvard?

Our structure, called MudWorks, was unveiled last week in front of the design school's Gund Hall, steps from Harvard Yard. It was completed in just seven days (see our blog at http://mudhall.wordpress.com/).

That makes it sound easy. Those 12-hour days were spent shoveling 50 tons of earth into wooden forms resembling giant cake molds, and packing the dirt down layer by layer with handheld and electric-powered ramming tools. Mud construction doesn't use much carbon energy, but plenty of the human kind: We had 140 volunteers from the GSD and nearby architecture schools. There's a reason they call this work backbreaking labor, and I have the sore shoulders to prove it.

Construction didn't always flow as smoothly as the mud. The Boston dirt we obtained from a local supplier was wetter than what Anna was used to, and the pneumatic rammers more powerful than Bangladeshi hand tools. At one point, volunteers had to be dispatched by taxi to Home Depot to bring back 600 pounds of gravel to lighten the mix.

But when the forms came off, our doubts lifted with them. The main wall was black as coffee, its corners sharply creased. As the mud dried, it turned a luscious elephant gray, with streaks of orange and cream. Textured and craggy, the material looked alive, particularly in contrast to the bland backdrop of Gund Hall's concrete facade. We could hardly keep from running our hands across the surface, which felt like suede.

Technically, MudWorks is an art installation, not a building, since we didn't have time to apply for a city permit. But while there's no roof, the installation does have an important function. Its main wall enfolds the windswept plaza at the busy corner of Quincy and Cambridge Streets, and transforms it into a cozy public space with niches and benches where people can kick back and, presumably, contemplate the potential of earth construction.

If Anna had her way, everyone would live in mud houses and work in mud office buildings. "I really think you have to work with the material to appreciate the strength, the simplicity. It's like sandcastle building," she enthuses.

The world, especially the developed world, will need some convincing.

Despite all the talk about sustainability in design schools, mud is still overlooked as a viable material. It's assumed that it doesn't wear well, that it isn't appropriate for cold climates, that it isn't suitable for multistory buildings, and that it looks primitive. Dirt may be cheap, but earth construction is labor intensive.

Except for the labor issue, those concerns don't appear to bear out. Martin Rauch, an Austrian earthworks artist who flew in to help oversee MudWorks' construction, has completed nearly 50 rammed earth buildings over the last two decades, including his own home in the Swiss Alps. His lovely Chapel of the Reconciliation in Berlin is reminiscent of the concrete architecture of Tadao Ando and Peter Zumthor, but much more green. You need lots of fossil fuel to make concrete.

Rauch has developed several tricks to prevent his mud structures from weathering. For his three-story house in 2008, he inserted horizontal courses of stone every few feet to deflect rain and snow. Inside, the smooth clay-coated walls and waxed floors make it look like a house out of the latest issue of Dwell.

Rammed earth is just one form of mud construction. Many architects have had success using mechanically compressed mud blocks, which are as hard as fired bricks. Rauch has also been experimenting with prefabricated rammed earth panels. Because they can be made in a factory, labor costs are lower.

When rammed earth walls start to get craggy, he says, you can always plaster over the surface with more mud. One image Rauch likes to show in his lectures is a six-story German apartment house in Weilburg built of packed earth. Completed in 1836, its skin is still baby-smooth.

So far, the Philadelphia region hasn't seen any mud buildings, according to architects specializing in green construction. "I've had a few clients inquire, but nothing has crossed the finish line," said Scott Kelly of Re:Vision Architecture. A big obstacle has been the labor costs. Still, he's eager to give rammed earth a try.

Holding a clump of dirt in your hand, it's hard to imagine how the crumbly substance could be transformed into a safe and durable building material.

Garret McGowan, the Boston contractor who provided support for MudWorks, had his doubts. "I didn't think the dirt would get hard," he told me, but he became a convert. "If I didn't have a house that was fairly new, I'd give this a shot. It's a product you can get right around the corner."

He shouldn't have been surprised. People have been building with mud since ancient times, and many structures still stand. Mission Dolores, San Francisco's oldest building, was completed in 1791 and has survived fires and earthquakes, including the biggie in 1906. The American Indian houses at Chaco Canyon and Mesa Verde are even older. Half the world's population still lives in earth structures, according to Eartharchitecture.org.

Unfortunately, many are crudely built, especially in Third World villages where mud is seen as a symbol of poverty. Even in America's Southwest, famed for its adobe houses, the skill has been lost among American Indians, says Mark Goldman, an instructor of green technology from Taos, N.M., who volunteered at MudWorks. "It's ironic that a Jewish builder like me is the one that is trying to keep this tradition alive," he says.

Because unemployment is high in American Indian areas, and people need jobs, Goldman believes earth construction can be a real alternative. In 2007, Las Vegas architects Lucchesi Galati designed a major museum using rammed earth construction, the Desert Living Center.

It's one of the few earth buildings to receive a LEED rating from the U.S. Green Building Council. That, too, is ironic, given that the organization is supposed to promote the use of local building materials. Nothing is more local than dirt. Many projects use the material straight from the site.

Given that we've already seen movements to encourage locally grown food, locally produced beer, local merchants, maybe it's time to add dirt to the list.

Contact architecture critic Inga Saffron at @ingasaffron and isaffron@phillynews.com.