For 16 years, Colleen Corrigan has sold bathing suits -- skimpy, bright-yellow bikinis and matronly, navy-blue one-pieces -- from her cramped shop on the ground floor of the Woodward Building at 15th and H streets NW in downtown Washington. She shares the building's retail floor with purveyors of African masks and Christian books, a liquor store, and a barbershop.

The eclectic collection of merchants stands out in a neighborhood where retail spots are occupied by a cell phone store, a Starbucks, a high-end jeweler and a men's tailor that serves the government crowd.

As D.C. rents are skyrocketing and builders are driving every building to its most profitable use, the Woodward Building is the last of an era -- a building a block from the White House that still relies on window air-conditioning units, has a little lobby newsstand that sells coffee for 89 cents a cup and counts a private investigator among its tenants.

"I love this old building," Corrigan said. "I have 16-foot ceilings, big showcase windows; there's no standard awnings, and I can put my own sign outside. You can be unique here."

That will all end at the end of the year, after tenants will be forced to leave so the owner can gut it to create a property more in line with its upscale neighbors.

The Woodward Building's owner, SJG Properties, plans to fill it with 187 high-end apartments renting from about $1,300 a month for a studio to $4,500 a month for a 1,500-square-foot unit.

On the floor where Corrigan sells her swimsuits, the landlord hopes to lure a sit-down, white-tablecloth restaurant and nationally recognized retailers such as Ann Taylor or a men's clothing store. Once the $25 million project is completed, retail rents will likely about double, to $40 or more per square foot from an average of $23 per square foot.

The historic building was built in 1911 by the family that started the Woodward & Lothrop department store chain. In its day, the building housed some of the District's leading law and accounting firms and insurance companies.

It is on a stretch of 15th Street NW once known as "little Wall Street." Buildings around it already have been through their facelifts. A block away, the Bowen Building, constructed in the early 1900s, recently underwent an $80 million renovation that preserved its facade. The owner of the Woodward Building spent $20 million to redo the Southern Building, just across the street.

Until now, the Woodward Building, with its ornate marble columns and Roman numerals across the main entrance on H Street NW, has remained relatively unchanged. The lobby still has cast-iron chair rails and black iron handrails along a wide marble staircase.

In the past few decades, however, the brick and limestone building has grown dusty and moldy, the ledges outside its windows covered in pigeon droppings, as gleaming new office buildings have lured away its more prestigious tenants.

Upstairs, where the window air conditioners groan to keep up and the restrooms are not always in working order, the office tenants include a temp agency, a prison outreach program and the Vegetarian Society of the District of Columbia.

"I guess we were the lowest-priced, and that's why they came, and I think a lot of buildings are stuffier than we were," said S. Jon Gerstenfeld, president of SJG Properties.

The tenants agree.

"You won't find another building like this," said Grace Malakoff, president of the D.C. chapter of the League of Women Voters. "It's cheap, but it's comfortable. All the neighbors are wonderful. They're all poor. They're all trying to make their part of the world a little better."

The nonprofit group came to the Woodward Building six years ago after hopscotching through offices in Northwest that were too expensive. The league pays $1,100 a month, including utilities, for a 577-square-foot office on the fourth floor. Malakoff's workers keep the windows open in the winter, even when it's snowing, because the radiator makes the air so dry.

"This is a no-frills building," said Robert Ivanoff, a vice president at Liberty Towers, an eight-person company that manages cell phone towers in 16 states from a sixth-floor suite about the size of a three-bedroom apartment. The company plans to move to a newer office near the World Bank headquarters in downtown Washington.

The Woodward Building once had as many as 120 tenants. Over the past six months, some of the office tenants have moved out, making the upper floors ghostly. The cherry wood doors of Suite 400 say "Bradley Woods & Co." in chunky silver letters, but behind the doors is an empty room with light bulbs dangling from the ceiling and bare concrete floors.

Some of the remaining tenants lament that the Woodward Building will become just another generic high-rise residential project with chain stores on the first floor.

"We offered something different in the middle of all this conservatism," said Houston Arrington, who runs a women's boutique that features racy, going-out-to-club clothes. He sells black and pink thongs and a few items that he sews himself, including a long, red Lycra dress for $169 that he said was similar to one worn by movie star Catherine Zeta Jones.

Some of the retailers looking for space worry they will lose their customers if they move. And some office tenants and shop owners are shell-shocked at the going rate of real estate.

"It's very hard to find another spot," said Varinder Kr. Dutta, whose Woodward Liquors store has been in the building for more than 40 years. "Nobody wants to have a liquor store in their building anymore. And if they do, they're asking too much. To pay the $40 a square foot these landlords want, you have to make some more money."

Owner Gerstenfeld said he would welcome back his current retail tenants when the new building is done in two years "if they're available," but he acknowledged that "some of them aren't quite the image of the new building."

SJG Properties has owned the Woodward Building since 1968 after Gerstenfeld paid a partnership $4 million for the property.

"There was a lot of unrest in the city back then, and some broker called me up and offered me the Woodward Building," Gerstenfeld said. "At the price he gave me, it was like a gift. I just couldn't pass it up."

Gerstenfeld, the oldest son of a New York rabbi, grew up in Washington. He worked as an engineer for a construction company and bought and sold rowhouses in Dupont Circle on the side. In the early 1960s, he quit his job and started his own development company, which his daughter, L. Ashley Gerstenfeld, now helps him run. In the past three years, the company worked with D.C. developer PN Hoffman to develop four luxury condominium and apartment buildings in the 1400 block of P street NW.

Gerstenfeld doesn't quarrel with tenant complaints that he hasn't kept up the Woodward Building in the past few years.

"The bathrooms are a mess," said Gerstenfeld. "And the air conditioners are just window units because for years we've been planning to remodel it.

"Now we think the time has come," Gerstenfeld said. "It's come to the end of its useful life as an office building."

Dana Hedgpeth writes about commercial real estate and economic development. Her e-mail address is hedgpethd@washpost.com

Colleen Corrigan, right, has sold bathing suits at her Bikini Shop for 16 years.

Jan Minkarelli gets his hair cut at Anton's barbershop, a 41-year tenant.

Varinder Kr. Dutta owns Woodward Liquors, a four-decade building tenant.

Tsege Gebremriam is co-owner of Woodward News and Coffee Bar.

SJG Properties plans to renovate its Woodward Building at 15th and H streets NW. The old office building's eclectic tenants will have to relocate at year's end.

After the renovation, SJG Properties hopes to lure a sit-down restaurant and nationally recognized clothing retailers to the space now partially occupied by Colleen Corrigan's swimwear shop. The bikini store and other eclectic tenants distinguish the Woodward Building from so many District offices housing cell phone stores and Starbucks coffee shops.

Tsege Gebremriam is co-owner of Woodward News and Coffee Bar. The 1911 Woodward Building has an arcade-style lobby.