Dive into the rooftop pool of the Pegasus Apartments -- 13 stories above downtown Los Angeles -- and the first few strokes probably will seem remarkably familiar.

Swoosh. The chlorine stings the eyes. Its smell permeates.


But soon swimmers are likely to realize there is something different. The squeak of bus brakes is audible. An air-conditioning unit on a nearby building hums at a near-constant pitch.

Then there's the office building across the street. At the edge of the pool is a view of a floor-to-ceiling window behind which is visible the clutter of computer cords, paper and mess. Clearly, its owner wasn't prepared for surveillance.

In the midst of a building binge, downtown Los Angeles is ushering in the era of the rooftop pool. As existing buildings are renovated into residential units and facilities are built downtown, rooftops long reserved for the unmentionables of city life -- air-conditioning units and elevator controls -- are being transformed into urban oases, courtesy of designers' imaginations and Southern California's sunny climate. Pools are the sun-drenched stars of those oases.

A host of new downtown buildings have rooftop swimming pools in their plans -- including the 17th-story pool at 1100 Wilshire, where an office building is being converted into condominiums, and the sunny, seventh-story pool at the Toy Factory Lofts, a former downtown warehouse that has an impressive view of the downtown skyline.

At a meeting of downtown developers earlier this year, almost everyone in the room seemed to be suffering from pool envy, as builder after builder showed off plans for elaborate swimming holes on the tops of their buildings.

Many developers credit the success of downtown's Standard Hotel -- whose rooftop pool and bar quickly became a hip gathering place after the hotel opened in 2002 -- with the push for pools up high.

The Standard's pool is still so busy some days that guests are sent to the Pegasus, its neighbor to the south, to swim in the apartment complex's rooftop pool.

"The fact is, every hotel across the country is doing something on its roof if possible," said Andre Balazs, the hotel's owner. "The Standard downtown set a unique example, and everyone would like something like that."

Including a rooftop pool in designs for residential projects, said several developers, has become de rigueur -- an amenity as common as a business center or concierge.

"We kind of are looking at [the rooftop pool] as an amenity that is a requirement to lease or sell the building, because all of our competitors are doing that," said Mike VanEtten, vice president of construction for Forest City Residential West.

Pacific Electric Lofts, Santee Court and the Medici also boast rooftop pools. So will the Brockman and the Eastern Columbia, under construction.

Rooftop pools are not inexpensive. Adding thousands of pounds of water onto the weight requires structural engineers to get creative.

Often, the pools are shallow -- 3 or 4 feet deep at most. And many of them are perched atop platforms, allowing their weight to be better distributed across the span of the buildings -- and preventing costly leaking if the pools overflow. The Pegasus even added a succulent garden at one end of its roof, to prevent huge numbers of people from disturbing the balance of the roof.

But many builders say those sacrifices are necessary -- both to compete with other projects downtown and to create a spot where residents can gather.

Paul Solomon -- a partner in Linear City, which developed the Toy Factory Lofts in the downtown arts district and is in the process of renovating the Biscuit Co. building, on the site of the former Nabisco bakery -- said rooftop spaces offer a place where residents can breathe and share a common space. Both of the company's projects feature rooftop pools and gardens.

"Whether intended or not, a really wonderful aspect of these rooftop pools or parks is that they foster community in an urban context," Solomon said.

Kate Bartolo, senior vice president of development for Kor Group, echoed that sentiment. She promised that when the Eastern Columbia opens next year, the turquoise tile building's rooftop pool will be a place where residents will "get to know each other. We wanted a gathering place," she said. "It fosters that feeling of a neighborhood."

The rooftop at the Pegasus, said resident Miguel Fletcher, was a selling point for the building when he decided to move downtown two years ago. Now, the security consultant, 25, swims there a few times a week, usually at sunset.

"Sometimes, at night, you can see people working" in the buildings nearby, he said.

Fletcher said the rooftop pool was one more way in which downtown has transformed itself into somewhere hipper and more vibrant than it has been for a long time.

"You can get that element of being at the beach in the middle of the city," Fletcher said. "You can throw off the suit and jump into the pool in swimming trunks -- all in the middle of the high-rises."

Miguel Fletcher takes a sunset swim in the rooftop pool at the Pegasus Apartments in downtown Los Angeles.