TEMECULA -- Builders are starting what they say is one of the most energy-efficient housing developments in Southern California, though its prospects are uncertain in what has become the worst real estate slump in a decade.

Woodside Homes plans to build as many as 260 houses in two tracts of the Wolf Creek master-planned community, just east of Pechanga Parkway. Woodside is offering a preview Saturday of the three that have been completed, on Lone Pine Road just north of Patricia Birdsall Sports Park. Buyers have committed to 50 of the houses that are still under construction, a Woodside official said.

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The houses feature solar panels; roofs with radiant heat barriers, an enhanced form of insulation; and windows that reduce heat transmission by 73 percent, according to Woodside and its subcontractors. Most appliances in the homes are designed to be 35 percent more efficient than state building code requires, says Southern California Edison, which is involved in the project and supplies electricity to most of Riverside County.

Edison said Woodside has been particularly proactive in using higher standards for energy efficiency. The Salt Lake City-based company has similar developments in Menifee and Romoland.

Other such developments include Del Sur in Rancho Bernardo, where all homes include energy-saving appliances and at least 20 percent are fitted with solar panels, the Del Sur developer said.

"All of this is going to be mandatory, we believe, in the next few years," said Jan Percival Lipscomb, who represents builders there and in several other developments in San Diego County. "That's where things are going."

Since January 2006, builders in Edison's territory have completed 967 homes that beat energy-efficiency standards by 35 percent, according to the utility. Such energy-efficient houses can qualify for $2,000 state grants, although typically that is just a fraction of what builders pay for thicker insulation, high-tech windows, tankless water heaters and other such features. And builders can pass the extra costs on to buyers, they acknowledged.

But those features can represent savings of up to $200 a month in energy costs, depending on the size of the house, said Tim McGinnis, president of Woodside Homes' California subsidiary. The Woodside homes in Temecula, which range in size from 2,700 square feet to 3,300 square feet, may use as much energy as smaller houses, but less than half as much as similar large houses, he said.

That can be a big advantage when the market is flooded with cheaper foreclosures, McGinnis said. Banks own about 3,100 of the 5,000 houses and condominiums now listed for sale in southwest Riverside County, according to the Multi-Regional Multiple Listing Service and Foreclosureradar.com, a subscription service.

And roughly half of the houses selling recently have been foreclosures. The listing service showed houses of 2,700 to 3,300 square feet in the same ZIP code selling for an average of $382,000 last month, compared to the $390,000 to $450,000 that Woodside is asking for its homes in Wolf Creek.

"People think they can get a good deal on a foreclosure, but it doesn't have solar power," McGinnis said. "We offer a product that's very unique."

Energy efficiency can also help buyers when they apply for mortgages, McGinnis said. Wells Fargo's mortgage division, a partner in Woodside's project, adds 2 percentage points to the portion of a buyer's income that goes toward loan payments. A buyer who earns $5,000 a month, for example, might normally qualify for a mortgage with monthly payments of $2,000; under the program with Wells Fargo, McGinnis said, the buyer would be assumed able to handle a payment of $2,100 a month.

Additionally, Wells Fargo can build state rebates into the interest rates that borrowers pay over the years, the bank said.

Contact staff writer Chris Bagley at (760) 740-5444 or cbagley@nctimes.com.