As Evanston residents and aldermen voice concerns about developments from proposed marinas to apartment buildings, a new initiative could use the high level of development to create more affordable housing for middle- and low-income families.

The new inclusionary zoning ordinance would require developers to set aside a certain percentage of residential units to be sold at an affordable rate — in exchange for financial incentives and other breaks for developers. But the policy could lower profits for some developers by as much as one third.

Proponents of the plan, backed by examples of inclusionary zoning across the country, said despite the possible decreases in profits for developers, the policy would not have an adverse effect on Evanston’s housing market. And as municipalities from coast-to-coast adopt inclusionary housing programs, some local developers urged caution and consideration.

“If you are taking 25 percent out of someone’s pocket, that ain’t chump change,” said Andrew Spatz, of Adas/Spatz Properties. “The way affordable housing works is that there needs to be an angel. You’ve got to have responsible, sensitive developers, and there is probably a pile of about two of them.”

David Hovey, president of Optima, Inc., which has several major developments in Evanston, said he understands these concerns. Hovey stopped short of saying the policy would decrease development but said it would definitely make it more difficult to build in the city.

“Everyone has to kind of evaluate (inclusionary zoning) against the need for affordable housing, which I think most recognize as a good idea,” he said. “I’m not saying they shouldn’t do it, I’m saying that yes, it would be more difficult to build.”

But more than 200 communities across the country have inclusionary housing programs, and the evidence shows the programs don’t hurt development, said Nicholas Brunick of Business and Professional People for the Public Interest, the firm that helped Evanston officials draft an inclusionary housing proposal.

“There are many developers developing in those programs and continuing to make money and doing just fine,” he said. “The sky isn’t going to fall here. Development can continue and you can start to produce some affordable housing for the populations that you care about.”

In Boston, which enacted an inclusionary zoning policy in early 2000, 264 affordable housing units have been built out of a total of 8,000 units built since the policy was adopted.

Although there was some concern from developers, most of them supported the program, said Tim McGourthy, the director of policy for the Boston Redevelopment Authority.

“While there may have been some resistance, it was not wholehearted,” he said. “There were a lot of developers who have supported the policy and it has been very successful since implemented.”

A key to getting developer support is granting density bonuses, which allow developers to build more market-rate housing units than they would normally be allowed to build, said Conrad Egan, president and CEO of the National Housing Conference, a housing policy organization based in Washington, D.C.

Egan said a carefully designed policy must balance the size of density bonuses, the percentage of the units set aside for affordable rates and how affordable those units will be.

“The trick is how do you design the ordinance so it doesn’t pull against but goes with the flow of development and adds an additional component of affordable housing,” he said. “If you are not granting sufficient density bonuses and if you are requiring a level of affordability that’s so deep that resources are unavailable to reach that level, then you are going to have an ordinance which is hard to implement.”

Although balancing the three factors is difficult, a National Housing Conference report released last month indicated that California has succeeded, Egan said. The report looked at communities in the Golden State and concluded that in most cases there was no effect on the level of development.

But Evanston may have some difficulty finding the appropriate balance.

Egan said density bonuses are the most effective cost offsets, but Evanston aldermen have expressed reservations about this option at city meetings. And there is nothing stopping developers from crossing city lines and doing business in towns without inclusionary zoning programs, he said.

But Brunick, of Business and Professional People for the Public Interest, said that as long Evanston’s inclusionary zoning policy is predictable and clear, developers will still flock to Evanston’s strong housing market.

“People want to live there so developers want to develop real estate there,” he said. “The majority of the evidence out there shows that inclusionary zoning does not have a negative effect on development.”