Preservationists are set to clash with the company redeveloping the Domino sugar refinery on the Williamsburg waterfront at a Landmarks Preservation Commission hearing today. As part of the second-largest development in Brooklyn, which will include five 40-story towers, the developer, Community Preservation Corporation Resources, is seeking to add a five-story glass structure onto the roof of the Domino building, which was given a landmark status in September.

The developers are aiming to create an 11-acre complex with 2,200 housing units, including 660 that will be dedicated to “affordable” housing. The plan also includes 120,000 square feet of retail space, 100,000 square feet of community facilities space, 1,500 indoor parking spaces, and several acres of open space. The nine residential towers, which will surround the refinery, are designed by architect Rafael Viñoly. Today’s hearing will focus exclusively on the fate of the iconic refinery, a building that has come to symbolize New York’s faded industrial legacy. Increasingly, northern Brooklyn’s waterfront is lined with tall glass condominiums.

The director of advocacy and policy at the Municipal Art Society, Lisa Kersavage, applauded the developer for its support of landmarking the refinery but said she felt the proposed design, by the architectural firm Beyer Blinder Belle, was untenable.

“We need to see this as precious and be more careful how we treat this building, and this very large glass addition just plunked onto the top of it is just not appropriate,” Ms. Kersavage said.

The president of CPCR, Michael Lappin, said the glass addition is appropriate and is required to make the project economically viable.

The developer bought the site for $56 million in 2004, and it did not oppose efforts to have part of the factory landmarked, which means that any significant changes to the building must be approved by the 11-member commission.

“There is an enormous cost to preserve the building. We are trying to create some economics that absorbs that cost. It is reasonable to spread some of that around,” Mr. Lappin said.

The refinery was built by the Havemeyer family and had been in operation since the 1880s before finally shuttering in 2004. At its peak, it had the capacity to produce about 950 million pounds of sugar a year.

A major point of contention at today’s hearing will be the fate of the Domino sign, which faces the New York City skyline, but the developers said no decision on its future has been made.

The landmarks commission can vote to reject the proposal, propose modifications, or approve it outright.