Architect Eric Strain designed a desert-compatible custom home, model, for an ordinary tract size in Boulder City. The house was never built because the buyer sold the land. Strain's design, below, put most of the glass on the building's north side to minimize summer heat seeping in through sunlit windows. The northern exposure also had a view of Lake Mead. Photo by John Locher. A small display window shows the straw bale inside the walls of Barbara Luke's home in Blue Diamond. Her house is not part of a tract. Architects here don't foresee straw bale catching on as a wall system for tract housing. Photo by John Locher.

Tract housing in Southern Nevada isn't going to transform instantly, like a pumpkin into Cinderella's coach. The process will be incremental, driven by prices for materials and energy, predict builders and architects.

New features and construction methods that save energy will migrate gradually from commercial to custom residential. From there they will trickle down to high-end tract homes.

Frank Wyatt, president of Pinnacle Homes, explains why.

"Can I afford to put it (energy features) in a house that costs $300,000, that people are struggling to buy?" Wyatt asks. No, he said, but pointed out that if a builder puts the same innovations into a $600,000 house, the price hike is a smaller percentage of the total price -- which makes it more palatable, especially to the well-heeled buyer.

Next, the marketplace will shake out which energy improvements mean the most to the mass of consumers who are on a tight home-buying budget. Several experiments already are under way to ferret out the information.

Pinnacle Homes in Las Vegas in 2005 built two almost identical homes. They share a floor plan but have key differences in the choice of wall system, air conditioning equipment, water heater, etc. The home with the bundle of energy-saving features even produces its own electricity, through a rooftop solar system.

From November through May, basically last winter, that home took 62 percent less electricity from the utility company than did the conventional baseline home. University of Nevada, Las Vegas engineering professor Bob Boehm, whose students are monitoring the two houses, expects the energy-efficient home to demonstrate even greater savings in summer, when air conditioners are gulping electricity.

In Borrego Springs, Calif. -- a desert town with extreme summer conditions similar to Las Vegas -- Clarum Homes just launched a demonstration project of four homes, each with a different package of energy-saving features. Clarum and a federal Department of Energy lab will monitor the homes for a year after move-in to see which features are the most cost effective. Clarum describes itself as California's largest zero-energy home developer. A zero-energy home is designed to produce as much energy as it consumes, even though it is still connected to the local utility company's power grid for backup.

A local pioneer and risk-taker is Frank Woodbeck, who is preparing to build a seven- to eight-home development in the southwest valley. To be called Enchantment Way, the small tract's high-end homes will have solar power and an alternative wall system. He says the firm already has its land and financing but is still evaluating wall choices. He expects the homes to be completed by fall 2007.

As more builders decide energy efficiency is a requirement to succeed in business, the innovations slowly will become standard features, interviewed parties agree. Tom McCormick, president of Astoria Homes, concludes, "If a builder thought they could get a clear advantage over the other builders, somebody would be doing this."

Two kinds of would-be buyers already have a hard time getting in the home-ownership game in Las Vegas. Brian Gordon of Applied Analysis defines them as "people entering the job market" and people "moving here from elsewhere not bringing a significant amount of wealth," perhaps because they sold a house in a region with lower real-estate values.

For these groups, other housing options are likely to emerge. Expect row houses, say recently retired UNLV architecture professor Richard Beckman and Astoria's McCormick. "Row homes are something every builder is looking at," McCormick says. Developers can fit more units on an acre of land when it's row housing versus single-family detached. The higher density allows them to spread the high cost of land over more buyers. Row houses are similar to townhomes -- a row of dwelling units side by side, sharing walls -- except a row house generally has a private backyard while a townhome often shares common outdoor space with neighbors.

Row houses are a larger share of the housing stock in places like Boston, Philadelphia, New York and San Francisco; and people from those locales who move here are already familiar with the concept, Beckman emphasizes.

Row housing may become the new way for a young buyer to get a starter home. The format can be energy efficient in that each unit has fewer outside walls -- and less loss of heat in winter or unwanted gain in summer.

Not many Southern Nevada builders have done row houses because insurance for this housing type was hard to obtain. Construction-defect litigation is more likely in residential projects where land and buildings are held in common ownership, according to McCormick. But some contractors and builders say the insurance industry here is evolving to encourage rowing housing again.

Another option for families who cannot afford conventional single-family housing is what national housing-trend researchers are calling the "generational house." Several related households pool their money to qualify together for a larger home, which may contain several master bedroom suites. Parties who, alone, couldn't afford better walls or a solar-power system may be able to if they band together

On the other hand an energy-wasting trend may emerge if Las Vegas housing prices go so high that lots of buyers start moving to outlying areas with the intention of commuting daily to Las Vegas. Poor housing location, in that case, will raise vehicle fuel consumption. Land-use decisions heavily influence transportation costs, which account for a third of U.S. energy consumption, according to the Rocky Mountain Institute.

"Drive till you qualify" is how Alan Matheson describes the hunt for housing amidst urban sprawl. People buy on the outskirts of a metro area because housing prices are lower, but they still work in the metro core. Matheson is executive director of the Coalition for Utah's Future and Envision Utah, organizations that designed and are implementing a "quality growth" strategy for the greater Salt Lake area.

A Southern Nevada example of indirect energy waste induced by housing location is the phenomenon of people with Las Vegas jobs moving to Pahrump -- and keeping their Las Vegas jobs -- just so they can qualify for federal home loans intended for rural residents.