Miami-Dade County has created project bonuses for developers who volunteer to build affordable housing, and Miami is doing the same through its Miami 21 citywide rezoning.

Developers will be able to plan taller buildings with corresponding square footage increases if they incorporate affordable units in the housing pool, according to Miami 21's benefits program.

For development proposed in the city's most urbanized areas, benefits range from 12 stories for properties otherwise restricted to eight floors and unlimited height when the maximum height is 48 stories.

Bonuses are limited, however, by abutting uses. And bonuses can also be bought by developers who contribute to the Miami 21 Public Benefits Trust Fund. The money would go toward other affordable housing construction.

Miami 21's benefits program mirrors the county's bonus program.

Elizabeth Plater Zyberk, dean of the University of Miami's School of Architecture and Miami 21's master planner, said the benefits strategy, which also encourages green construction and historic preservation, is intended to broaden the pool of properties where affordable may be built to both waterfront and inland properties.

Height and square footage bonuses theoretically would allow developers to improve their bottom line by increasing the total number of units. The volume would offset the lower prices on affordable units and help mitigate land and construction costs.

But the challenge of getting developers to buy in is great when factoring in the cost of infrastructure and construction and the challenges of finding buyers who meet program qualifications and qualify for loans.

Not to mention the housing slowdown.

In the first quarter, no developers participated in the county's benefits program.

There were no new applications for residential zoning in unincorporated areas despite county efforts to recruit developers to build near public transportation hubs such as Metrorail stations and along major highways like U.S. 1 in the southern part of the county.

County Commissioner Barbara Jordan, who fashioned and championed the voluntary program, said participation is being undercut by the housing downturn.

She said the program needs more time to produce results. She said she has seen it work in other states like Virginia, Connecticut and North Carolina.

The county also is in the midst of a housing scandal over money intended for affordable housing units that produced little to nothing, and the county's housing agency is being taken over by the federal government due to mismanagement.

The question of whether blighted neighborhoods like Miami's Overtown and Liberty City can be transformed through zoning is being tested through Miami 21.

Few homes have been built in Liberty City to replace hundreds of public housing units demolished years ago with promises of something better to come.

Habitat for Humanity is building single-family homes in the area for people who wouldn't be able to afford them otherwise. The architect said blocks surrounding Habitat's homes will get similar zoning to encourage similar development and hopefully give residents a chance to buy in.

But having higher-density zoning has been a plague in some neighborhoods like Highland Park, Miami's first subdivision near the Civic Center along Northwest 11th Street and Ninth Avenue.

The area is zoned to allow some of the city's densest projects, which has encouraged developers to buy up land. It is populated mostly by single-family homes.

Lots intended for condominiums at the height of the boom now sit vacant, said Anne Manning, executive director of Habitat for Humanity of Greater Miami.

Manning, who has built 53 homes in four years in Liberty City, said the final version of Miami 21 should reflect the historic nature through zoning of neighborhoods like Highland Park.

She said it also would help if Miami 21 provided bonuses to mitigate infrastructure upgrades.

She said she has been lobbying the city to build sidewalks alongside the Habitat homes, but the ones that have been built are sidewalks to nowhere because neighboring properties don't have them.

Lack of infrastructure can add as much as $30,000 to the cost of a new house, she said.

"It's a cost drain," Manning said of adding infrastructure costs to the tab for housing construction. "It's cost prohibitive for most people."

An infrastructure bonus in blighted neighborhoods could influence developers and should be considered for Miami 21 and other municipal zoning modifications, Manning said.

North Miami Beach is working on a plan that would have city crews build the infrastructure and give developers access at a discount to encourage redevelopment.

City Manager Keven Klopp said the city is not specifically targeting affordable housing with the proposal, but it could apply.