Philadelphia switched over to a new zoning code Wednesday, culminating a four-year effort to simplify the development process and upgrade the city's housing stock for modern tastes.

The 384-page manual replaced now-antiquated and cumbersome zoning regulations that had been in use since 1962, when Philadelphia still saw itself primarily as a manufacturing center. The new rules, worked out by a citizens' commission, are meant to support Philadelphia as it rebuilds its residential neighborhoods and evolves into a city of universities, medical centers, and high-rises.

Many large cities, including Chicago, Miami, and Denver, have recently overhauled their zoning codes to reflect changes in the way Americans live and work. Philadelphia's code has been similarly crafted to make its neighborhoods more walkable, discourage parking, and allow residents to enlarge their homes and add roof decks more easily.

"We wanted to build a code that would be good for the 21st century," said Stella M. Tsai, a lawyer with Archer & Greiner who served on the Zoning Code Commission and attended a news conference Wednesday.

"There were an awful lot of people out there who bet this wouldn't happen," Alan Greenberger, deputy mayor for planning, told the gathering at 19th and Callowhill Streets, where the 10-story Granary apartment building is under construction.

Mayor Nutter said the site was chosen for the event because it is one of a dozen large projects under way in the city, and is a sign that Philadelphia is emerging from the long real estate bust. He predicted that the code will encourage more development, saying it "will make it easier for developers to get projects moving and create jobs."

Although a mix of developers, lawyers, and neighborhood activists served on the commission, it was developers who were particularly interested in streamlining Philadelphia's zoning rules. Because the old code was obsolete, nearly every project required a variance from the Zoning Board of Adjustment, a process that was both costly and time-consuming.

Richard DeMarco, a zoning attorney who served on the commission, said in an interview that more projects would be built "by right," without having to apply for a variance. By making the process more simple and predictable, he said, more companies will want to build in Philadelphia.

The old code had become bloated with amendments and overlays, and had nearly 700 pages. Its replacement is organized in a more straightforward manner, and is written in simple English.

Some of the provisions in the new code include:

The standard height of rowhouses will increase from 35 to 38 feet.

Garage-fronted rowhouses will be banned on most streets.

Architectural reviews will be mandatory for all projects over 100,000 square feet.

The code is only a start. The city still must update its maps to reflect the reduced number of zoning classifications. That project will take at least five years, Greenberger said, although the city plans to concentrate on the neighborhoods seeing the most new construction.

The effort to rewrite the code began in 2007 when then-Councilman Frank DiCicco persuaded his fellow legislators to include a proposal for a new zoning code as a ballot initiative.

Approved by voters at the tail end of Mayor John F. Street's administration, the project got off to a slow start. Only after Nutter came into office, promising to reform the city's development and planning process, was the commission able to hire consultants and begin the laborious process of writing a new zoning manual.

Yet the adoption of a new code was nearly derailed last year when some neighborhoods objected to the prospect of increased density.

Only after the Nutter administration agreed to drop several related provisions - including those that allowed people to rent apartments in their homes and operate bed-and-breakfasts - did City Council agree to vote on the new zoning manual. It was approved in December, with the Aug. 22 start date.