Take the home of Ron Carswell. Perched on a hilltop in the Tucson Mountains, it's heated by the sun--the same sun, of course, that warmed prehistoric dwellers in these mountains many centuries back.

That's not to say there aren't a few updates, such as straw-bale insulation and a precise alignment with the sun's seasonal shifts. There's also an aluminum radiant barrier that holds interior heat in the winter and resists up to 90 percent of the summer sun's ultraviolet rays.

Carswell stands by 11.5-feet-high windows that are really the soul of this remarkable home. Down the hill is another studio, also made with straw-bale construction. "I run 5,500 square feet on roughly $100 a month," he says with a smile.

Learn the secrets of this award-winning designer and his remarkable dwelling on the Tucson Innovative Home Tour/Tucson Solar Tour 2007. Each year, the sprawling soiree highlights the best and brightest in energy efficiency, featuring 15 beautifully clever dwellings, along with a bevy of experts.

Folks like Ron Carswell are on the front lines of the green revolution sweeping the country. Though we've seen such fads before, ever-rising energy costs may give this latest sustainability upswing some shelf-life. And it's symbolized by homes on this tour--fashioned to maximize energy savings, reduce pollution and use recycled materials whenever possible.

There's certainly no doubt about the need. According to the Environmental Protection Agency, traditionally constructed buildings are responsible for nearly 40 percent of carbon dioxide emissions, 12 percent of water use and almost 70 percent of America's total energy consumption.

Those numbers grow even more critical as the current number of buildings in this country--5 million commercial buildings and 76 million homes--is slated to climb to roughly120 million in the next three years.

To avoid an energy disaster, the new generation of buildings taps a few primary concepts. They include:

· Lot design and preparation. By making critical design decisions from the start, builders create a truly green home at the ground level. This includes limiting the home's impact on surrounding plants, on water drainage and on the soil. It also means orienting the home to take full advantage of the sun.

· Efficient resource use. Finding energy-efficient materials--and not wasting those materials--is essential. Then it's important to design a durable home, one requiring a minimum of maintenance resources.

· Water conservation. Along with cooling, this is among the most crucial elements to consider for a desert home.

· Energy efficiency. Installation of energy efficient systems--from appliances and lighting to air conditioning and heating--is integral to the green home--and results in hefty long-term savings.

To make these elements official, the U.S. Green Building Council offers a certification process for energy-efficient, environmentally friendly homes. Under its Leadership in Energy and Environmental Design program, or LEED--the gold standard for sustainable building--the system provides intensive design guidance and helps promote green building.

And while Tucson is a leader in this growing niche, green building is on a national upswing. In 2004 alone, more than 14,000 green homes were built across the country. Meanwhile, the National Association of Home Builders has been devising a certification program similar to LEED. It offers annual "green building" conferences and comprehensive guidelines for conservation-minded contractors.

Locally, Pima County, Oro Valley and the city of Tucson have been using green-building standards on new buildings. Meanwhile, our three state universities have also embraced green building; there's already at least one green school in the Tucson Unified School District.

So it's no surprise that this city boasts a bevy of green pioneers--and a slew of energy-efficient success stories, according to Paul Huddy, home tour organizer. "The key to these kinds of houses," he says, "is passive solar design, high thermal mass and the orientation of your house.

"With straw bale, for example, Ron Carswell has really good insulation. And then he put in a system for radiant floor heating, and he was going to front-end that with solar water heaters on the roof."

But then came one of those discoveries that solar aficionados relish. "Ron discovered, after he had moved in, that the passive solar design was working so well that he didn't even need the backup heat." Huddy says with a chuckle. "It's just a very impressive house. Definitely one of the best in Tucson."

At the same time, construction costs were only about 10 percent more than traditional construction. But the savings don't stop there. The house is also fitted with LED and compact fluorescent lighting for lower energy use. Outside, low-water native plants are irrigated with a drip system.

The Carswell house is cooled by a pair of evaporative coolers, themselves shaded by honeysuckle and jasmine vines--infusing the house with wonderful scents. Double-glazed windows line the south wall. Doors and windows are framed in wood, with skins of aluminum for easy maintenance.

There's also a holistic touch here, toward low-impact living. Bedrooms are in the west wing, with an interior frame of steel that doesn't bear a load, meaning that the floor plans can be tweaked--walls easily yanked out and moved--without a terrible amount of work. Nematodes grown locally protect the home from termites. Then there's the foundation, 8-inch-thick concrete resting on a bedrock of solid rhyolite.

But in the end, it all comes back to those basics that have worked for a millennia, such as simple orientation: "One of the most important things," says Carswell, "is that you'll see a shadow line, because there's a 4-foot overhang" above the windows.

"From equinox to equinox, there's no direct sunlight on this glass. And if you build a model of your home, and you study it after sunrise on the equinox, and at noon and at sunset on the equinox, then you know exactly how to perfectly orient your house for passive solar design."