A change in New Jersey's affordable-housing regulations, limiting the amount of senior citizens' housing that can be counted toward low-income requirements, is causing developers to rethink their plans in a market reeling from the economic downturn.

"Being in development nowadays is like trying to hit a moving target," said Arthur Corsini Jr., a partner in Fieldstone Associates, a development company in Bridgewater. "The [low-income housing] requirement is a line item, like drywall. But we don't know where we stand, so how do we factor it in?"

Where some towns in New Jersey once could count all of their new senior housing toward the Council on Affordable Housing's 2018 goal of 116,000 new units around the state, those exemptions are now capped at 25 percent, following a Superior Court ruling in 2007 that found the policy discriminated against families.

In areas such as Haddon Township, where Fieldstone is working on a residential-and-retail project on a former industrial site, development has effectively been put on hold as town planners and attorneys try to ascertain how much affordable housing they will be required to build in the coming decade.

"One planner calculated it one way and another planner calculated it another way," said Catherine Ward, an attorney hired by Haddon Township to oversee its COAH process. "It's a very complicated issue, and these townships are forced to go out and hire expensive people to help them with this."

The current round of rule changes is being challenged by New Jersey municipalities in 22 separate legal appeals, according to the Department of Community Affairs.

But that's all just sour grapes, say low-income housing advocates.

Kevin Walsh, associate director for the Fair Share Housing Center, a nonprofit advocacy group in Cherry Hill, argues that the rule change is effectively closing a loophole that has allowed local officials to keep low-income families out of town.

"Towns prefer to have age-restricted housing because you don't have kids, and education's expensive. The only thing worse than kids is poor kids," he said. "The whole game is to keep families out."

COAH was created in 1985 as a means to allow New Jersey's poorer, largely inner-city families access to the high-performing schools, parks, and other staples of suburbia.

So far, approximately 50,000 homes have been built through the program, Walsh estimates.

One challenge for towns is figuring out where to put up the tens of thousands of low-income homes left to be built.

"We're the most densely populated state, crammed between two big cities," said Michael Cera, senior legislative analyst with the New Jersey League of Municipalities. "A lot of what is left is deed-restricted or preserved. We're kind of running out of space."

The question in Haddon Township, a 2.8-square-mile enclave known for its Victorian homes and picturesque downtown, is whether Fieldstone's Towne Center at Haddon Township development will even go ahead.

Once home to a diaper-washing facility, which leaked solvents and other chemicals into the ground that are now being cleaned up, the six-acre acre site in downtown Haddon Township sits vacant.

The original plan called for 201 apartments or condominiums to be sold or rented to "young professionals," Corsini said. But that was based on the belief the town already had satisfied its low-income housing requirement of 75 units by 2018.

A portion of that requirement will be covered by the existing senior housing and other state-mandated credits, but Haddon Township officials won't know how much they have left to build until attorneys go before the judge overseeing their COAH plan, likely early next year.

At that point, town officials will have to decide whether they can allow Towne Center to go ahead as planned or must require Fieldstone to integrate low-income units into the development, risking the possibility the developer will walk away.

"We've been on this project for seven years. We've got a lot invested," Corsini said. "We never had any plans to do COAH, but if it were to be required, we'd like to see how many units they're talking about."

Contact staff writer James Osborne at 856-779-3876 or jaosborne@phillynews.com.