When Roseann Sullivan says she lives in a co-op, she's usually greeted by a blank stare. Although common in cities such as New York, cooperatives are far outnumbered here by apartments and condominiums.

But when she says she lives in University Square, she's more likely to see nods of approval, especially from longtime East Enders who pass by nearly every day on Fifth Avenue in Oakland.

A resident of University Square 2 for more than 21 years, the retired literacy coach for Pittsburgh Public Schools put her research skills to good use last year in compiling a history of the red-brick building for its 50th anniversary.

"Within the next year, a swanky tenant-owned apartment house will be constructed within walking distance of Pittsburgh's cultural center in Oakland," the buildings' architect, Arthur E. Tennyson, wrote in the April 1954 issue of Charette.

"Swanky" could also describe the lot's previous occupants, two 1870s mansions designed by Philadelphia architect Isaac Hobbs for members of the Carrier and later Schmertz families. An adjacent property was the site of the Alinda Preparatory School and later, Duquesne Gardens. By 1986, when Ms. Sullivan and her mother were looking to move from Cathedral Mansions, University Square still looked pretty "swanky."

"I had always admired this building. It was so well-kept," she said.

Others apparently agree. Current residents include former U.S. Rep. Bill Coyne, scientists and authors Ernest Sternglass and Marlin Mickle, and surgeons and missionaries Jose and Violeta Alba. Former residents include the late Samuel A. Weiss, a Common Pleas Court judge, and the late Eugene "Jeep" DePasquale, a Pittsburgh City Council member.

So what's so great about University Square? Its exterior is understated -- simple, square, midcentury Modern, which happens to be hot right now but isn't as eye-catching as Fairfax Apartments, the older Tudoresque building across the street. Interiors have low ceilings and little or no moldings or baseboards. Ms. Sullivan's small kitchen retains its original stainless-steel countertops, but she has replaced the cabinetry, as have most other residents.

Ms. Sullivan also moved doorways in her two-bedroom, one-bath apartment and replaced a long hallway with a series of closets. The most dramatic change was in the back bedroom, now called the Black and White Room. With design help from Arthur Moser & Associates, Ms. Sullivan put up crown molding and toile wallpaper depicting Asian scenes.

Her friend Ruth Glasser, who lives in one of only two doubles in the building, remodeled and repainted every bit of her 2,000 square feet of living space before she moved in nearly six years ago. With four bedrooms and 3 1/2 baths, the apartment is actually larger than the Squirrel Hill house she shared with her three children and late husband for 40 years.

Visitors are struck immediately by the spacious, light-filled living room with its soft neutral color scheme, comfy furniture and electric fireplace. The kitchen and adjacent breakfast room saw the biggest changes. New white appliances replaced an old oversized refrigerator and range with pullout burners.

Removing most of a wall between the two spaces and moving two sets of low cabinets to another wall created a much more open eat-in kitchen. The small table in the breakfast area has ingenious leaves that pull out to accommodate eight people. That same number or more can dine comfortably at the large table in the adjacent dining room.

In a cooperative, residents technically don't own their apartments, only shares of stock in a nonprofit corporation. So how can they remodel? The reality is that they can sell their units. Prices of seven sold over the past two years have ranged from $48,500 in July 2006 to $195,000 in September, according to RealSTATS (www.realstats.net). Residents' leases are automatically renewable, and all utilities and taxes are included in a single monthly fee that ranges from $600 to $1,300, depending upon apartment size.

Renovations and improvements must be approved by the co-op board, but as long as they aren't structural or visible through the windows, they're usually approved. To hold down noise, residents must have carpeting in at least 90 percent of their floor space, according to Richard Ackerman, senior vice president of Arnheim & Neely, managing agent for University Square.

Joseph Wassermann, president of the co-op board of directors and a 10-year resident, said he and his wife first visited University Square while attending friends' parties there. Besides the location, this retired teacher at the Western Pennsylvania School for Blind Children appreciates its spacious bedrooms, one of which he uses as a study.

Ms. Sullivan enjoys her small balcony, where she and her neighbors have watched runners from the Great Race and Pittsburgh Marathon pass by. She noted that residents hold a bi-monthly poetry series in the lobby, and last year they spoke about their careers and hobbies in a lecture series.

"It's a very friendly, very close-knit community," she said.