The white buildings are rising from the construction site south of the Kennedy Center, but the long-awaited expansion — two years delayed and costing some $50 million more than originally planned — is now expected to be completed in 2019.

Kennedy Center Chairman David M. Rubenstein said the expansion project — called the REACH — should be finished next May. An arts center official said a grand opening is planned for September 2019.

“We hope by this time next year it will be open,” Rubenstein said before the Spring Gala on Sunday featuring Mavis Staples, Bruce Hornsby, Neko Case and Alison Krauss. “Thank you for supporting it so far.”

The first new space in the 47-year history of the national arts center, the Steven Holl-designed project will provide intimate indoor and outdoor performance opportunities, officials have said.

The original $100 million design has grown to a $175 million effort that will open 27 months late, thanks to changes in design and a major sewer project in the District.

The expansion will add 60,000 square feet of classroom, rehearsal and performance space on the four acres to the south of the white marble arts center. In addition to the three pavilions, the project includes a reflecting pool, a grove of trees, a sloping lawn that will allow for outdoor screenings of performances and a pedestrian bridge over Rock Creek Parkway connecting the arts center to the riverfront.

A Kennedy Center spokeswoman said Rubenstein was being “aspirational” in his remarks at the gala, which honored actor Gary Sinise and philanthropists Eli and Edythe Broad and raised $1.8 million for the arts center. Officials plans to announce more information about the project — including what REACH means — next month.

Kennedy Center officials hosted a ceremonial groundbreaking Dec. 4, 2014, and announced that the new space would open May 29, 2017, the 100th anniversary of John F. Kennedy’s birth. The original fundraising campaign sought $125 million, including $100 million for construction and $25 million for programming.

The project hit its first hurdle that afternoon, when the first of two review boards declined to approve the design, citing issues with the wharflike pavilion on the water. Holl and arts center officials moved the water pavilion to land, and the revised plan was approved in May 2015. The changes caused a 15-month delay of the planned opening — setting it for September 2018 — and a new fundraising goal of $175 million was announced. The project is being paid for entirely with private donations.

A second issue arose in 2015, when Kennedy Center officials and executives at D.C. Water decided to undertake part of D.C. Water’s Clean Rivers Project during the construction to minimize future effects on the site. The program seeks to reduce sewer overflows into the city’s waterways. D.C. Water’s work began in March 2106.