Atlanta's most famous volunteer home builders are raising their game in more ways than one.

Not only are they building more houses each year, which has made the Atlanta affiliate of Habitat for Humanity one of the most successful in the U.S., but they are tackling two-story houses for the first time.

Today, about 90 volunteers will begin the Atlanta affiliate's first foray into building town houses. Habitat is building upward for the same reason for-profit builders in urban areas do.

"Land is so expensive, we have to figure out ways in which we can provide for and serve more families in this area," said Larrie Del Martin, the executive director of the affiliate.

The plot of land they are building the six town houses on in the Sylvan Hills neighborhood would have accommodated three single-family houses, she said.

"So moving to town homes will help six families instead of three," she said. "We expect to do more of this in the future, because that is just a wise use of land."

And there will be even more types of housing in the future, Martin predicted, including cluster homes and condominiums.

"We just continue to have to be smart if we are going to provide opportunities for working families," she said.

The town houses will have about 1,250 square feet and include a bedroom and bathroom on the ground floor in case residents are handicapped. The first group of three town houses should be finished in eight weeks, and then workers will start on the second set of three houses.

The home buyers will bear the typical price — sweat equity in the construction and a 30-year no-interest loan to pay Habitat back.

The construction will be a learning process for three teams working shoulder to shoulder and at times on scaffolding, but Atlanta's volunteers have proven up to the task in the past 25 years. It's the strength of the volunteer base that has made the affiliate one of the most successful, Martin said.

The Atlanta group was the first in the country to reach the 500-house milestone and the affiliate expects to complete the 1,000th house later this year. The international organization was founded in 1976 and is based in Americus.

In 2004, the Atlanta group also began building all houses to high environmental standards.

Ray Maynard, the affiliate's director of construction, said workers recycle construction waste, such as shingles, which are ground and laid as a paving base for driveways. Teams use building methods that consume less wood and take pains to make the houses energy efficient by doing things such as using extra insulation and caulking to minimize air leakage. One such house saves about 30 percent on heating and cooling costs, he said.

"That's a pretty good amount they save on their energy bills that they can spend on other things they need," Maynard said.