Harold L. "Spike" Yoh Jr. built his family business, Day & Zimmermann. With his late wife, Mary, he raised a business family.

Three of their sons now own and operate Day & Zimmermann, which maintains nuclear power plants, guards U.S. embassy staff in Asian and African war zones, builds missiles for the military, and matches engineers to Silicon Valley software developers, among other jobs, under the motto, "We do what we say."

With $2.5 billion in yearly sales and around 45,000 workers — construction and engineering, plant operations and maintenance, staffing, security and defense — D&Z ranks with Wawa, Asplundh, and Vanguard Group among the largest private companies based in the Philadelphia area.

Private companies don't have to tell us much about their cash flow, let alone interpersonal relationships among the owners. But Spike's son Bill Yoh has written a book — Our Way. It's not a business history — the 117-year-old company publishes those every few decades. The cover says it is "the life story of Spike Yoh." Really, it's a transgenerational family saga, drawn from a hundred interviews — family and friends, but also people who left the company and some who compete with it.

Spike ran D&Z from 1976 to 1999, taking over from his father, who started in the staffing business, bought Day & Zimmermann in 1961 (its engineers designed Hershey's Kisses wrapping machines, bridges and bomb factories, power plants and ship repairs), and made friends with Ronald Reagan. The story folds in drama and loss alongside triumph and growth, and serves as an argument that it's possible to succeed at work and family, with all the stress.

There is plenty of privilege assumed in the book: Yoh kids go to Haverford and Agnes Irwin, Duke and Penn, and summer in lovely places even when they are young and feel short of cash. The Yoh brothers worked their way into big jobs — son Hal (the third Harold) has been CEO since 1999; Bill is chairman of Yoh, D&Z's contract-staffing affiliate; their brother Mike runs the munitions plants; Jeff sold his share to his brothers and now owns fire-and-flood restoration company Jenkins Services, which he's converting to employee control, while running his Christian nonprofit, Servants With a Heart. Not all top D&Z managers are Yohs; the brothers don't expect all their kids will follow them as managers.

There is also resentment and sorrow. Straitlaced, family-loving Spike for years felt what Bill calls "vitriolic anger" at his self-centered, uncommunicative father, the original Harold, a Midwest farm boy turned much-married Main Line mogul. The family lost unhappy sister Karen, at age 42, in an accidental pill overdose; the Yohs blame themselves for failing to figure out how to keep her engaged.

As if in reaction to his father, Spike mated for life, doting on Mary, and put positive reinforcement next to tough standards at the center of his enterprise: "Spike had a way of putting his arms around you and making you feel you were part of the team," Bill says. As an engineer, Spike urged his sons and his bosses to focus on what's going on and why, not just what ought to be; the worker on the line "knows what's wrong," as Bill put it, and you'd better listen.

He says Spike taught that business "has a broader purpose" than enriching owners: "You have a responsibility to thousands of employees," and to clients, who in D&Z's case are often U.S. taxpayers.

Staffing, D&Z's largest line, seems extra-dependent on the individuals in charge. Yoh's Philadelphia-based rival CDI Corp., under longtime chief Walt Garrison — he and Spike "had great battles, they competed with integrity," Bill says — went public in 2000 at a valuation of $1 billion, but post-Garrison CEOs proved unable to boost profits, and CDI's board sold it to a private-equity firm last year for just $154 million. Hill International, another Philadelphia-based construction-staffing firm that went public, has also struggled since impatient investors forced out the founding Richter family.

The Yohs have broadened their definition of a private company, Bill says. "In my father's generation, it was, 'We want you to be part of a family.' Now, we talk more about diversity and inclusion. The tent flaps are broader." D&Z has "resource groups" for "military veterans, people of color, people with disabilities, LGBTQ. Rather than meaning, to fit here, you would have to be, act, and dress like the family, now you bring your whole self to work" and the company needs to show all are welcome, he added.

"One of our real objectives now is to imbue in our next generation a sense of ownership," whether or not each joins management, Bill says. "How do we imbue the responsibility and pride in the next generation?" One of the rising fourth generation of Yohs works in the D&Z IT group; another is at Comcast; a third plans to be a midwife. Some studied engineering. Six are high-school age and younger.

Last year, the brothers brought the teenagers together for a day of talks, games, and trivia. "Ostensibly they were learning about the business. Predominantly, it was about them doing things that were enjoyable together, so they want to have another meeting," Bill said.

The Yohs are working with consultants developing guidelines for families in business — what Bill calls "Familytics," a way to "look at the dynamics of family and the relationship to business. We are getting it trademarked." Spike taught the brothers "the value of getting more angles from which to examine an event or series of events"; writing the book, Bill turned the camera around, and says long interviews helped Spike became more understanding of his own father, realizing at last that "it wasn't that his father didn't love him, but the way his father was able to express support wasn't the way he was ready to receive it then."

Bill added, "And that's part of life. Everything needs context. Every person, every family, hopefully brings a lot of context."