DURHAM — The Ronald McDonald House of Durham will cut the ribbon Tuesday on a $6.8 million expansion that nearly doubles its size.

The charity, which provides children and their families from out of town a place to stay while they are treated at area hospitals, was still finishing construction Monday as it prepared for a ceremony to celebrate going from 29 rooms to 55.

The house on Duke University’s campus served 1,300 families in 2011, but had to turn away 700 because of lack of space. Executive Director Oie Osterkamp said he hopes the new rooms mean the house won’t have to turn anyone away.

“It offers us the opportunity to say ‘Yes’ instead of ‘I’m sorry,’” Osterkamp said. “What we are hoping is that we don’t have to say no at all, and if we do have to say it, we hope it’s just very, very little, because these families are going through so much.”

Osterkamp said that despite the fact that he’s still sharing his office with construction equipment, the new portion of the house is already 50 percent full.

The new part features two “immunization floors” for children who receive bone-marrow transplants and have other problems with immune suppression. The floors have play areas, a reading nook and an indoor tree house, designed to acclimate children to the real world while keeping them safe from disease.

The expansion also includes a chapel, a library, a computer room, a learning center, additional play areas and a board room.

All of the new rooms are designed for families who need to stay at least eight months. Each can house up to six people comfortably, Osterkamp said.

The expansion has been a decade in the making, said Dr. Joanne Kurtzberg, director of Duke Health Center’s Pediatric Bone Marrow and Marrow Transplantation Division.

Because of the extensive follow-up care so many children require, demand for rooms has long outweighed the number available, Kurtzberg said.

“The pediatric department at Duke treats children who come from all over the world for complex medical care,” Kurtzberg said. “In the case of our program, people come for transplants and need to stay in our area for six to eight months after the procedure because of the complexity of care after they recover and can’t be treated in their home community.”

About 10 percent of the pediatric marrow division’s children come from other countries, and those children usually need to stay a full year, Kurtzberg said.

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