Developer Donald Chiofaro says he is willing to make changes to a $1 billion development on Boston Harbor, including tweaking plans for open space and public amenities anchored by a signature public plaza. But he’s not willing to budge on the size of the 1.3-million-square-foot complex, which would include a five-star hotel, high-end condos and corporate offices.

“That’s what we need,” said Chiofaro, who withdrew an earlier proposal for the central waterfront site two years ago and went back to the drawing board. “If all we were trying to do was just build something, there are a lot of easier ways to do it. This is not just an ordinary opportunity; it doesn’t deserve an ordinary execution, and it deserves extraordinary attention to detail.”

Many aspects of the current plan remain up in the air, including the shape, exterior and cap designs for the 600- and 550-foot towers which would rise between the New England Aquarium and the Rose Fitzgerald Kennedy Greenway. In an interview, Chiofaro said he favors “interesting” tops for the buildings, noting he was criticized for the crenellated cone top and Palladian windows at his International Place office complex, built in the 1980s.

Updated Design Elements

What’s known so far is the new complex would have distinctive ground-level spaces. Equipped with a retractable canopy roof, the 27,000-square-foot Harbor Plaza running between two 600- and 550-foot towers is billed as a magnet for year-round activities and a new window on the harbor from the Greenway. Cafés or corporate meeting spaces are planned on the roof of both buildings’ lobbies, facing the harbor. A grocery store and pharmacy are candidates to fill 70,000 square feet of retail space.

The new design would open up street-level views of the harbor that are currently blocked by the eight-story parking garage that takes up virtually the entire 1.3-acre site. Corners of the towers’ lower floors along East India Row and Milk Street would be shaved off to improve view corridors, as recommended by the city’s waterfront activation plan. The Boston Redevelopment Authority is preparing new requirements from developers of waterfront properties improve public access and attractions along the harbor.

State regulations also require a minimum of 50 percent open space on direct waterfront parcels, something the current plan falls short of by about 2 percent.

It’s unclear whether state regulators would consider Harbor Square to be open space, given the retractable canopy. To qualify as open space, an area has to be “open to the sky” and accessible without building entrances.

“Will it feel open to the general public to enjoy?” said Vivien Li, president of the Boston Harbor Association. “Whether the state will allow that is not clear.”

Chiofaro said he is willing to drop the canopy plan if regulators require it, but argued that it will encourage more use of the plaza in the winter.

“If it’s open to the sky, who’s going to use it in January? So we took a page out of the stadiums that have roofs that open and close,” he said. “The most important thing is it’s open 24/7.”

Office Space Goal: Global Headquarters

While Chiofaro has not released detailed financial plans, he said the current scale and mix of uses is the minimum needed to make a profit. Boston-based Chiofaro Co. acquired the garage in 2007 for $150 million. The 1,400-space garage generates $9.5 million a year and would cost $150 million to put below ground under the current plan, Chiofaro said.

So far, the hotel and condos have drawn the most interest from investors, with the goal for the office space attracting a global corporate headquarters as anchor tenant for approximately 300,000 square feet.

Since unveiling the drawings last month, Chiofaro said he’s received unsolicited letters of praise from residents of the neighboring 40-story Harbor Towers condo complex, many of whom opposed his earlier plan because of its size. Chioforo withdrew a 1.5-million-square-foot tower proposal in 2011 amid a public feud with former Boston Mayor Thomas Menino.

While residents have complained about spoiled views, Chiofaro said the replacement of the garage with a landmark development will increase residential property values.

The latest proposal also comes with offers to secure Harbor Towers’ future ability to weather extreme coastal storms. The existing garage, built as part of the complex in the 1970s, contains key utility systems for the condos, including boilers, in its basement.

Environmental studies predict the property would be flooded in a Hurricane Sandy-magnitude event that hit Boston at high tide. The equipment could be relocated above ground in the new building.

“It is a big deal. We’ve made several different offers to solve the problem and we will at the right time,” Chiofaro said.

Harbor Tower trustees have not formally responded to Chiofaro’s presentation last month to the municipal waterfront planning committee. In a statement last week, the Harbor Towers garage committee said, “We appreciate all the hard work and creativity that went into the Chiofaro presentation. We have a lot of questions about things like where the open space should go, what constitutes open space, and whether this much density is appropriate on the waterfront.”

Email: sadams@thewarrengroup.com