Doug Block has gone where few filmmakers dare to tread — into the murky waters of his parents’ marriage.

The veteran New York documentary maker had no intention of poking a camera into his family history, even after his mother died suddenly in 2002 just a few weeks after coming down with pneumonia at age 78.

But in the next few months, his father announced his engagement to the non-Jewish woman who had been his secretary 40 years earlier and put the family homestead in the Long Island commuter town of Port Washington up for sale.

Block and his sisters were shocked, not least because the exuberant fellow making these major moves bore little resemblance to the emotionally inexpressive engineer they’d known all their lives.

They were in for another surprise. Going through the basement with their father, clearing out 50 years of accumulated belongings, they came across a trove of diaries their mother had secretly kept. In those pages, Block discovered a side to her he’d never imagined—and the genesis of his one-of-a-kind film.

Block’s first-person documentary, “51 Birch Street,” begins its theatrical run Friday, Nov. 3 at the Opera Plaza Cinemas. The provocative film, which had its Bay Area premiere this summer in the San Francisco Jewish Film Festival, is slated for an HBO broadcast next year.

“I would say that what makes it a particularly Jewish story is simply that [we] were a kind of archetypal Jewish family,” Block said during his festival visit. “The synagogue was kind of the center of [my parents’] social life.”

Block was raised secular Reform in what was then a new suburb, where he got more than his fill of the nouveau riche.

“I felt quite alienated from my Judaism growing up,” the filmmaker said. “I felt a hypocrisy between what Judaism espoused in principle and the fairly wealthy, well-to-do way that the Jews were living. They talked one way and behaved another.”

At home, Block and his sisters were close to their mother. Their father was at the office during the day, of course, and after work he often holed up in his basement workshop.

“I didn’t even know where my father stood politically,” Block says. “He sort of took pride in being hard to figure out, about letting you know where he stood on things.”

On the other hand, Block thought he knew everything about his mother. In her diaries, though, he encountered her ambitions, longings and frustrations.

“I think my mother was just like a lot of Jewish women — really smart, and she should have had a job she loved,” Block said. “She would have been great at that. But it wasn’t a time when women went out and got jobs, particularly with all those kids. So it got channeled into other stuff, like running a super household.”

On one level, “51 Birch Street” is a portrait of 1950s suburbia, and traditional nuclear families where roles were clearly defined. That family dynamic still has echoes all over the world, we can assume, or else the Al-Jazeera International Documentary Film Festival in Qatar wouldn’t have included the film in its program. (Block did not attend the screening.)

Block addresses on camera the sticky issue of whether to read his mother’s notebooks, and then whether to include passages in the film. He justifies both decisions as part of the process of reconciling his experience of his mother with the woman hidden in the diaries.

“Finding out who my mother was,” he muses, “I felt like I got a lot of insight into this generation of women, [and] particularly this generation of Jewish women.”

“51 Birch Street” opens Friday, Nov. 3 at the Opera Plaza Cinemas, 601 Van Ness Ave., S.F.