Dewberry Vice Chairman Barry K. Dewberry, left, with his father, Sidney O. Dewberry, who is stepping down as chairman. (Jeffrey MacMillan/Capital Business)

Sidney O. Dewberry, whose self-titled professional services firm played a key role in developing many well-known projects in Northern Virginia, is stepping down from his role as chairman, the company is set to announce today.

Barry K. Dewberry, Dewberry’s oldest son and the firm’s vice chairman, has been elected chairman, effective April 13.

At 84, Sidney Dewberry, who remains on the board, said he is ready to pass the reins to his 60-year-old son, and said he hopes that the 1,800-employee company will remain family-owned and run.

A civil engineer by training, Dewberry co-founded the business in 1956 in Arlington. As Northern Virginia grew into a major suburb, the company played a significant role, working with well-known local developers, such as Milt Peterson of Peterson Cos., and on prominent projects, including Tysons II, Fair Lakes and the Filene Center at Wolf Trap.

Dewberry also was involved in community affairs, particularly at George Mason University, where the civil and environmental engineering department is now named for him. He is rector emeritus of the university’s board of visitors and a past recipient of the Mason Medal.

“He’s one of the dozen or so people that really made Northern Virginia happen in the last 50, 60 years,” said John T. “Til” Hazel Jr., a land-use attorney who started working in Fairfax around the same time as Dewberry.

Though both Sidney and Barry Dewberry said the company’s culture won’t change, they endorsed expansions in its services. From its roots as an engineering services firm, Dewberry has expanded into services such as disaster assistance, hazardous materials management and, more recently, cloud-computing.

In an interview last week, Sidney Dewberry said the company first started seriously diversifying in 1990, when it hit a recession that made it hard to collect money it was owed. The company learned a lesson and began rethinking its mix of work.

Before 1990, about two-thirds of Dewberry’s work was related to land development; before the most recent recession, it was down to about 15 percent, and since 2008, it has shrunk to less than 10 percent, he said.

Now, transportation is one of the company’s largest lines of business, representing about one-third of its revenue. The company worked on the Dulles Toll Road and more recently the Intercounty Connector in Maryland.

Starting in the late 1960s, Sidney Dewberry brought in partners to own a share of the company. But he said he slowly bought them out, regaining full ownership in the mid-1980s.

He redistributed ownership of the company, providing 20 percent to each of his four children and retaining 20 percent. Unlike partners, who pull out profit each year, Sidney Dewberry said his family keeps much of the money in the firm.

He said he plans to give his share to his children before his death.

Within the next 15 years, Barry Dewberry, who joined the company in 1975, said he plans to pass down the company’s leadership once again, perhaps to his younger brother Tom, who just turned 39, or to another younger family member.