BOULDER — When the Iron Flats development east of downtown Boulder was designed in 2001, it marked a shift in the city's zoning.

"It was one of the first true mixed-use projects in Boulder," said Kelly Davis, managing principal at OZ Architecture. "There was a lot of conversation about mixed use at the time — banks couldn't figure how to finance it and tenants couldn't figure out how to utilize it.

"Everything was more urban prior to that."

Mixed-use zoning blends a variety of land uses together in one area. It can include single-family detached homes of various sizes, townhouses, condos, retail stores and restaurants, as well as civic and cultural facilities. They might all be located within walking distance of each other.

At one point a portion of the land, which is adjacent to Boulder's Whittier neighborhood and four blocks from the Pearl Street Mall, was slated to be turned into a park by the city of Boulder, according to Davis.

As principal in charge of Iron Flats, Davis was in on the project from the beginning.

"Then they got on board with this new urbanization, walkable neighborhoods and mixed use," he said. "I give Phil (Shull, president of Deneuve Construction Services, the design-build contractor of Iron Flats) a lot of credit for making it happen.

"The fun part of this project was working with him. He's a very eclectic guy who's made a career of interesting remodels and repurposing of buildings."

Shull was out of the country and unavailable for an interview on the project at press deadline.

Iron Flats is a 72,000-square-foot project that includes 35,000 square feet of commercial space including the Nature Conservancy's Boulder office. It also includes 27 housing units, which are comprised of loft condominiums, townhomes and combined living /working units which range from 1,000 to 1,700 square feet.

"It's well established and never had a problem with occupancy," Davis said.

He credits a lot of the ongoing appeal of Iron Flats to its location and design. Each section of the project was created to fit in with the areas to which it was adjacent.

The buildings that meet up with the Whittier neighborhood, for example, are more residential. "The character of the buildings is designed to be complimentary with the residences there," he said.

The pedestrian trail connects on the west end through the park for public access. "We wanted it to be permeable so people could walk through," Davis said. "The whole thing feels very accessible."

"It's not crowded in like a lot of the new developments in downtown Boulder," said Kaylene Veron, broker with Prudential Real Estate of the Rockies, who also lives in Iron Flats. "And there's all kinds of different architectural designs."

Veron lives in the Butterfly Building, one of the five residential buildings. Features of the six separate units include balconies, rooftop decks and 10-foot high ceilings.

"It has an older-time look to it — an Early American style."

Having lived in her place since 2005, Veron describes the feeling of the neighborhood as "like the way neighborhoods used to be. You sit on the porch and talk to the neighbors."

Since the Iron Flats subdivision is so close to downtown, she rides her bike to work and walks to the Farmers' Market — a big draw for anyone who lives in Boulder.

With her other hat on, Veron is the listing agent for a unit at 2336 Spruce St. The 1,331-square-foot property, a two-bedroom loft, is listing for $537,500.

"It's in great condition for a resale because it was built with quality materials and structure," she said. "The fact that someone doesn't have to come in and replace or remodel increases its appeal."

The property has had three showings in three days with one interested party coming back.

Leanne Goff, broker associate with Staufer Team Real Estate, is listing another property in the subdivision — one where the original buyer combined two units.

The resulting 3,987-square-foot condo features a universal design. "It means that there's access for all and visually attractive to everyone," Goff said.

The property is listing for $2.295 million.

"It's unique because a 4,000-sqaure-foot downtown condo is hard to find. It's also unique to Iron Flats because the others are 1,500 to 2,000 square feet.

"And even though the market narrows when a property is in the $1 million to $4 million range, we're having interest on this one," Goff added. "It really has a lot of amazing amenities."

"Sales in general in 2009 and 2010 were slow as indicated by the economy, and in 2012 they've been remarkably good," Goff said. "Iron Flats, however, really started picking up last year, ahead of the general market."

What's put the subdivision ahead?

"Iron Flats offers nice quiet homes for great prices," she said. "They're very spacious and near downtown."

"It seems even better now than at the time it was designed and built," Davis said. "Iron Flats is very successful economically, conceptually and functionally. It has really performed very well."