RALEIGH, N.C. — For many homeowners, an energy-efficient home is the stuff of architectural magazines, outsize budgets and wishful thinking.

But an increasing number of people with low incomes are living in high-efficiency homes and cutting their electricity bills in half.

In North Carolina, about 80 percent of low-income houses built by groups such as Habitat for Humanity and subsidized by a state housing program come equipped with features such as efficient appliances, heat-blocking windows, high-grade ducts and snugly installed insulation without gaps or breaks.

Some even come with solar water heaters, which can cost more than $5,000 for the appliance and rooftop solar panels.

The upshot is that low-income families, who often can barely afford a new home, have become pioneers in energy efficiency.

Energy efficiency — in appliances and home design — has been described as the “fifth fuel,” because it can keep down energy costs, reduce greenhouse gases and delay or eliminate the need for new power plants.

Homes built by Habitat and other charitable groups qualify for the federal Energy Star rating, the most commonly accepted standard for energy efficiency. The homes are small, typically under 1,400 square feet, and sometimes priced under $100,000.

The savings can be significant, because many owners of affordable homes are upgrading from older dwellings that were models of energy inefficiency.

What’s more, the Energy Star certification qualifies homeowners for an additional 5 percent price break on electricity bills from Progress Energy and a 2 percent discount from Duke Energy.

Loubrenda Duffy, a clerical worker who moved into a Habitat for Humanity home in Hillsborough, N.C., six months ago from a poorly insulated apartment, has seen her power bills slashed in half, down to about $80 a month this winter.

“There’s no airways, nothing. It’s sealed very well,” Duffy said of the three-bedroom home that she helped build. “I had to use more heat to keep that apartment warm. And the apartment was smaller.”

For years, commercial homebuilders didn’t see a market that would justify spending more on energy-efficient upgrades that are concealed behind walls, in attics and under crawl spaces.

Instead, when builders upgraded, they splurged on granite countertops and other luxury items to woo home buyers.

But with energy prices on the rise and growing awareness of climate change, energy concerns are entering the mainstream.

The nation’s biggest homebuilders are offering more energy-efficient models every year — in 2006 constructing about 21 percent of homes to the federal Energy Star standards, according to a study issued last week.

In North Carolina, Cimarron Homes, Anderson Homes and others build nothing but energy-efficient houses. But in this state, where electricity costs can be 25 percent below the national average, less than 3 percent of homes are built to Energy Star standards.

“To date, the market has not valued the energy savings the same way it would value a garage or an extra bathroom,” said Nick Tennyson, executive officer of the Home Builders Association of Durham, Orange and Chatham Counties.

When built into a mortgage, monthly savings from energy-efficient appliances and designs will often exceed the extra mortgage amount needed to pay for the upgrades.

Still, it can take 10 years to recoup the investment in efficiency upgrades that cost as much as $10,000, said Craig Morrison, president of Cimarron Homes in Durham, N.C.

“That’s an awful lot of money,” Morrison said. “The savings on utility bills are over time, and the additional value from resale, that’s later, too. Most people are looking for an immediate difference.”