Kapiolani Medical Center for Women & Children will open the first phase of an estimated $1 billion expansion Monday.

The $180 million Diamond Head Tower, the hospital’s largest building project since the 207-bed facility was built in 1978, is adding 200,000 square feet for a rehabilitation department, an outpatient clinic, and an education center for obstetrics/gynecology and pediatric training. Most, but not all, of the new tower will be opening Monday.

A pediatric intensive care and an adult medical surgical unit will open in September; a neonatal intensive care unit will open in October.

Roughly 80 percent of the space is completed, while the remaining 20 percent has yet to be built, including space for an employee fitness center, a $12 million emergency department, an imaging center and a $13 million kitchen and dining room facility. A new emergency room is to be added in 2017. Kapiolani’s current ER sees 45,000 patients annually.

Among the most important benefits of the expansion are larger, private rooms that will allow parents and caregivers to stay overnight, said Kapiolani CEO Martha Smith.

“What it really means to us is allowing families to stay with their children and their babies when they’re in the ICU (intensive care unit). That was the whole driver of this because right now our units are open, which means no private rooms. That means it’s very difficult for family members to stay at their children’s bedside,” Smith said. “Research shows that people heal better and faster when they have a loved one staying with them.”

The five-story tower, which is adding 36 beds to the 60-bed neonatal/pediatric intensive care units, was $60 million over budget based on original estimates of $120 million in 2014. The building, on the site of the hospital’s old parking lot, is designed to connect to a second tower that will be built on the site of the existing Bingham building, which is set to be razed this month.

“The original plan was to start at the Bingham building, but the construction guys said, ‘You need to build where the old parking structure is.’ That’s how we ended up with a bigger building than planned,” Smith said.

Lyrryx Bautista, a 13-year-old boy from Waipahu, was getting physical therapy this week in a small, crowded room in the aging Bingham building shared by four therapists.

Bautista, who became paralyzed from the waist down after jumping on a friend’s back and breaking his spine on the last day of school in May, often shares the former maternity room, which was converted into a gym, with other patients due to capacity problems.

“These rooms are pretty small, and we really need a bigger gym. The new building will have adequate space to allow the patients to really maximize their potential and have different options for doing their strengthening and mobility exercises,” said Susan LaFountaine, director of Kapiolani’s rehab services department, which is increasing to 8,000 square feet from 3,000. “The reason that the new space is so significant is because we’re the only pediatric tertiary care hospital in the state. This is the (only) pediatric rehab program for children like Lyrryx under the age of 18 who sustain injury and need inpatient rehabilitation.”

A second tower will house patient beds and services, including the operating room and laboratories, while the existing physicians building will be converted solely into doctors’ offices. The cost of the second phase of the project has yet to be determined.

“It’s cheaper to build a new tower than to try renovate the old one because of the technology and all the systems you have to have for a hospital as opposed to office space,” Smith added. “We built out on every bit of land we have — it’s a very tight footprint on 4.5 acres. In order to accommodate future growth, the recommendation was to build the building we did.”

The towers were designed to allow additional floors to be added in the future. The third phase of construction will include a new Punahou Street parking structure. The cost of the final phase also hasn’t been determined, but original estimates in 2008 placed renovations at at $800 million. That number has since grown as a result of project revisions and higher construction costs.

The hospital has hired more than 30 new employees for the new tower, in areas such as security, housekeeping, facilities and other support services. It raised more than $34 million to help finance the first phase and is preparing to kick off another capital campaign for the next part of expansion.

The massive redevelopment started with a $26 million parking garage built in 2013 on an adjacent 1-acre site, followed by groundbreaking on the new Diamond Head Tower in 2014. The entire project is expected to be completed in 2025.

“This is the only full-service specialty hospital for women and children in the state, and people need access to that care. They should not have to go to the mainland for it, so we’ve got to make sure we keep up with technology and continue to provide the care and services to people,” Smith said. “We definitely have a capacity issue that’s more related to population issues than to any particular group immigrating here. We’re a referral center for all hospitals on the neighbor islands, and the population in Hawaii has grown.”