Children’s Hospital in New Orleans is moving forward with a $250 million expansion onto the campus of the former New Orleans Adolescent Hospital on the other side of State Street, the first step in carrying out a master plan aimed at providing new and updated facilities for the hospital while protecting historic structures on the site.

The expansion has long been sought by hospital officials, who have had their eye on the 17-acre property since NOAH, which provided mental health services to indigent children and adults, was shut down by state budget cuts in 2009.

The $250 million project will allow Children’s to update its facilities to meet current needs and technologies, create a new emergency department and surgical suite, and expand its behavioral health unit.

“This is to provide space for where we are now and where we will be in the very foreseeable future,” said Mary Perrin, president and CEO of Children’s.

The hospital also plans to provide amenities for the neighborhood, potentially including walking paths and a meeting space that will be housed in a former gymnasium.

The project include a new critical care center, connected to similar units in the main building, as well as a new parking garage to reduce the number of cars forced to park on neighborhood streets. Those projects will require the demolition of six brick houses near State Street, many of which are in a dilapidated state, Perrin said.

Overall, she said, 84 percent of the square footage of existing buildings on the NOAH property will be maintained and reused for hospital functions.

The cupola-topped, five-story Renaissance Revival building at the center of the campus will be used for administrative space. Other buildings, including the two wooden cottages that are the oldest structures on the property, will be rehabilitated and maintained.

The first phase is expected to take about five years to complete. The next phase, which involves significant work on the existing Children’s Hospital building, would be 10 years down the road, while future developments would round out the master plan after 25 years.

Hospital officials are expected to go before the city’s Historic District Landmarks Commission on Thursday to ask for the buildings that are part of its master plan to be granted landmark status, giving them additional protection from demolition or alteration.

The hospital approached the expansion plans with a particular eye to the historic buildings and old trees on the site, said Brian Landry, senior vice president of marketing, public affairs and development for LCMC Health, the parent company of Children’s Hospital.

“We recognize the beauty of the campus and the historical aspects of the campus,” Landry said. “If the historic buildings weren’t here and these oaks weren’t here, you could envision the expansion being very different.”

The property has been the home of medical facilities since the 1880s, when the federal government built a Marine Hospital on the site to treat maritime workers. Most of the buildings that were part of that complex were replaced in the 1930s, including the main building at the center of the campus.

The hospital continued as a federal facility until 1981, when it was shut due to budget cuts and sold to Louisiana, which used it as a drug-treatment center before it evolved into NOAH.

The hospital was once again the victim of budget cuts in 2009, when Gov. Bobby Jindal’s administration shut it down in favor of sending patients to Southeast Louisiana Hospital in Mandeville, which was itself privatized a few years later.

Children’s first began leasing the NOAH property in 2012 under a deal that required it to be used for mental health services. While the hospital never had any intention of using it for that purpose, it maintained the lease with the intention of buying the property. The hospital purchased the property from the state in February 2014 for $29 million.

“I’m happy to say I think Children’s Hospital realizes it will be an asset to their operations,” said Patty Gay, executive director of the Preservation Resource Center, which was brought into the discussions on the project. “It is beautiful. It will be a soothing place for children and their families.”

Follow Jeff Adelson on Twitter, @jadelson.