John Abrams, founder of South Mountain Company, never thought he’d be a businessman. He never even really thought he’d be a builder.

Now nearly 50 years after moving to Martha’s Vineyard and building one of the largest integrated engineering, construction and design businesses on the Island, he’s about to retire as both.

“This started as a seat-of-the pants operation when I was 25 years old,” Mr. Abrams said in a recent interview. “I had absolutely no clue where it would go.”

The perpetually five-o’clock shadowed holdout from the hippie generation has transformed a two-person, New York city cabinet-making woodshop into a one-of-a-kind, employee-owned cooperative with a sprawling West Tisbury office space, and projects that span the Island.

Although Mr. Abrams isn’t officially retiring until 2022, the business that he spent much of his adult life building has entered a transition phase as they prepare for a future without him. The plan calls for Deirdre Bohan, a former bookkeeper, designer and current chief operating officer, to take over as South Mountain chief executive officer with a four-person leadership team by her side. The team includes the company’s four department heads: lead architect Ryan Bushey, energy and engineering specialist Rob Meyers, director of finance and human resources Siobhan Mullin, and director of production Newell Isbell Shinn.

John Abrams co-founded South Mountain Company when he was 25. — Jeanna Shepard

It’s a unique model that Mr. Abrams and Ms. Bohan say represents the business’s longstanding “first-among-equals” philosophy on leadership and decision-making. For instance, the company has 23 owners, all of whom are employees. That egalitarianism is also part of the legacy that Mr. Abrams will leave behind as the company’s unquestioned first-among-equal for the past half century.

Under his leadership, South Mountain has become known for building simple, energy-efficient structures, from high-end homes in Menemsha to affordable housing in West Tisbury. Mr. Abrams believes his homes are built to last, and as he prepares to step aside, he says the employee-ownership model ensures that the business was built to last too.

In other words, it’s a lot easier to pass the proverbial torch when there were already 22 other pairs of hands to help hold it.

“We have talked to a number of other companies about their leadership and ownership transitions,” Mr. Abrams said. “And what we’ve found is that the ownership transition is generally much more complex than the leadership transition. But we did that in 1987.”

South Mountain has a long history — over 5,000 words long, if you read their website — but the modern version of the business structure basically came into existence in the late 1980s. At that point, the company was a 10-person firm that had begun when Mr. Abrams and his partner Mitchell Posin arrived on the Island to build a home for a family member. They decided to stay, learning the trade while poring over instruction manuals for building passive-solar homes along the way.

Learning the business side of things was more difficult.

Deirde Bohan is an operations expert and master of strategic planning. — Jeanna Shepard

“The whole idea of starting a business was not really of interest to me,” Mr. Abrams said. “But after some years, a friend and mentor who loved our work said to me, are you making any money? I said no, we’re losing money on pretty much everything that we do. And he said, well, you’ve got a really unique idea here: subsidized housing for the rich. And I was like, wow, I’m going to learn about business.”

A decade later, they had grown the company to the point where two employees came to Mr. Abrams asking, essentially, for a partnership. He made them owners instead.

“It felt like if we did our job well, over time, this was going to come up over and over,” he said. “So I figured, let’s find a structure that welcomes people in.”

The employee-ownership model was born. Four decades later, and it’s part of the reason Ms. Bohan has risen from bookkeeper to designated CEO.

“All employees have the opportunity to become owners after five years, assuming it’s working out well,” she said. “So in some ways, it’s self-perpetuating. And hopefully, at the same time, we are creating future leaders for generations to come.”

Ms. Bohan never thought she’d work for a building or design firm either — let alone run one. She first came to the Vineyard to work summers during college. She spent eight years at the Black Dog before she saw a classified ad for a bookkeeper at a small integrated building company in Chilmark. With a background in computer science and accounting, and a budding interest in design, she decided to make the 25-minute drive for an interview. She hasn’t left.

“I had not anticipated that I would be assuming this role,” Ms. Bohan said. “But John and I have always been really values aligned.”

“She was the clear choice for CEO,” Mr. Abrams said, describing a detailed process that led to the choice.

Shortly after she started at South Mountain, Ms. Bohan had moved all the company’s accounting to QuickBooks and was looking for a better way to spend her work week. Interested in design, she decided to take night classes at the Rhode Island School of Design. She started the company’s interior design department, and ran it until three years ago, when she became chief operating officer.

While Mr. Abrams began with work boots on the ground, Ms. Bohan is an operations expert and master of strategic planning. She’s a strong facilitator, according to her co-workers, and can figure out what people are trying to say in order to implement it. Despite their differences, it’s also clear that Mr. Abrams and Ms. Bohan have much in common.

“I think it’s a lot about the employees,” Ms. Bohan said. “Respect for individual’s identities. And of course, creating beautiful things.”

In recent years South Mountain has expanded its expertise into energy, education and sustainability.

Unlike most design-build firms, according to Mr. Abrams, the company is really an architecture, engineering and building company. Only about 30 per cent of the employees work in construction.

“This Island is so full of amazing talent in architecture and building,” Mr. Abrams said. “But I think that integration is what’s different.”

South Mountain has also recently re-written traditional design-bid-build contracts to do master planning as well as construction and architecture work with a number of Island nonprofits, including Camp Jabberwocky, Island Grown Initiative, and most recently, Martha’s Vineyard Community Services.

That’s part of the reason for the company’s own recent growth and expansion. It was approved by the Martha’s Vineyard Commission last year to add employees and enlarge its office space and woodshop.

This time it will be Ms. Bohan, not Mr. Abrams, to shepherd the company through that growth.

“We’ve worked on this plan for almost a year,” Ms. Bohan said. “I’m excited that we’ve announced it. I’m excited about our new focus for the next couple of years. And I’m excited about sharing this journey with my colleagues.”

For Mr. Abrams, he’s just excited knowing the business is in good hands. Twenty three pairs of them, to be exact.

“This whole thing, this whole transition in leadership, is not a short sprint. It is more like a long journey across the country on back roads where you stop and see all the sites along the way,” he said. “But I suddenly had this notion that wow, this thing I had always thought about, of leaving the company in the best condition it’s ever been in, that was really possible. And it was happening before my eyes.”