The documentary as personal search, a non-fiction device that Michael Moore has employed to great success and Mark Moskowitz used so charmingly last year in “Stone Reader,” takes a family turn in Nathaniel Kahn’s film, a kind of cinematic essay recording his effort to come to a deeper understanding of his late father. But the picture is more than an attempt to achieve some individual accommodation with history, because the man in question, Louis I. Kahn, was also one of America’s most notable architects–not as productive as many, but in retrospect much admired and extremely influential–who died, in debt and anonymously, in a Penn Station restroom in 1974.

He was also, as it happens, quite an enigmatic fellow with a difficult streak and a very secretive side. Nathaniel investigates his professional life through interviews with other architects who knew him, including Philip Johnson and I.M. Pei, but also by visiting the relatively few structures he designed–among them the Salk Center in La Jolla, the Kimbell Museum in Fort Worth, and the national capital building in Bangladesh, as well as a boat equipped with its own concert shell–and studying his plans for projects never completed. Even these segments of the picture, however, are handled with a highly personal touch; the questions often lead to amusingly quirky answers, and the buildings and drawings are examined for their spiritual feel as much as their architectural stature. But while these sections of the film are lovingly done and engaging, the personal side of the subject’s life is even more fascinating. Kahn lived not only a double but a triple life, having not only a wife, Esther, and a daughter Sue Ann by her, but two more-than-mistresses–Nathaniel’s mother Harriet Pattison and architect Anne Tyng. Esther died before Nathaniel could interview her (it’s doubtful whether she would have submitted to questioning anyway, and at least he can incorporate bits of earlier footage of her), but he includes fairly extensive, quite poignant conversations with the other two women. And he goes further, talking to ex-students, former colleagues, even cabbies who used to drive his father to and from his office. (There’s also a brief snippet from Edmund Bacon, the city planner who vociferously condemns as impractical Kahn’s unorthodox ideas for the renovation of the Philadelphia downtown.) All the effort gets Nathaniel closer to his father, but the old man remains an elusive figure, never fully captured here any more than he was in the newsreel-like snippets taken while he was alive, which his son utilizes admirably. (We don’t hear much from Kahn directly, only about him from others.)

“My Architect” is a modestly appointed film that, from a purely visual standpoint, sometimes doesn’t match the extravagance of its subject. But the subject is nonetheless a fascinating one, and the perspective of a son’s odyssey gives the picture an emotional center that a more detached treatment could never have approached. A personal obsession has once again become a film that should appeal to an audience far larger than one.