Markus Zusak, the phenomenally popular Australian writer, worked on “Bridge of Clay” for two decades, essentially his whole adult life. Such perseverance is awe-inspiring but risky, for all the reasons this new novel makes plain.

The story — a full-throated paean to sibling affection — is about five brothers raising themselves as best they can. The narrator, Matthew, is just old enough to act as his brothers’ guardian in a town that expresses little concern for the well-being of these abandoned boys. Their house ripens into “a porridge of mess and fighting,” something between a locker room and a barnyard, where a mule has free rein of the kitchen. “Many considered us tearaways. Barbarians,” Matthew says. “We swore like bastards, fought like contenders, and punished each other.”

Zusak pours unbridled joy and chaotic violence into this house with its scrum of boys. But just below the surface of all that adolescent male vitality run crosscurrents of anger and misery. These kids lost their mother, Penelope, after a three-year battle with cancer. Their shattered father wandered off for good. The boys refer to him, when they speak of him at all, as the murderer — the man who killed them. “What we were,” Matthew says, “there’s nothing left.”

“Bridge of Clay” opens several years after that tragedy when their errant father returns for a brief visit. He wants to know whether any of them will help build a bridge in the old-fashioned style, by hand, without mortar. The brothers are incensed, but one of them, Clay, agrees to drop out of high school and work on this labor in the wilderness. So begins the tale of an obsessive partnership, an act of construction and reconciliation — a bridge across a river and a span across shared grief.

Zusak has created the voice of a man desperate to get everything down in his own raw poetic phrases. Matthew tells us he’s pounding out this story on an old typewriter he dug up in the yard, and earthiness still clings to his sentences. He sports a bold, unabashedly romantic tone, an attitude long nurtured by his mother’s fondness for the adventures of “The Odyssey” and “The Iliad.” Ranging across the decades, he describes his childhood — “the last vestiges of youngness and dumbness” — along with all he’s been told about his parents’ storied past and the horrible truth he learned only later. The result is a collage of charming, bracing and scarring moments in the tumultuous history of a once happy family.

Some of these incidents are complex, absorbing subplots, while others are precise, gutting vignettes from hospice, as when the toughest brother, Rory, “with the scrap-metal eyes,” suddenly looks up from the Monopoly board and asks, “What’ll we do without her?” Matthew can barely keep from crumbling in the face of “that look, so afraid, so despairing, and the words, like a boy in pieces.”

But despite how widely the novel wanders, Matthew’s real focus is Clay, the brother who bore the loss of their parents the hardest. Always quiet and sensitive, he developed into a taciturn, cruelly self-disciplined teenager. His devotion to running seems masochistic, and the same determination fuels his dedication to the bridge. He has become so saddled with sorrow that only the agony of physical labor — or, possibly, the satisfaction of making something perfect — can blot it out.

In Matthew’s telling, Clay is graced with Homeric greatness, tinged with mythic prowess and affliction. “His heartbeat stung in the stillness,” he says. “There was fire in each of his eyes.” It would all be too corny if Clay’s agony weren’t so visceral and Matthew’s affection weren’t so pure.

There’s much to love about this capacious novel, but there’s also so much. In addition to its obvious symbolic weight, the story feels freighted with those two decades of rewriting and revising. Clay’s bridge may be a creation of elegant utility, but “Bridge of Clay” is an extravagantly overengineered story. The burden of that excess is exacerbated by Zusak’s decision to scramble the chronology of events. Admittedly, this is sometimes effective, as when chapters about Penelope’s escape from Eastern Europe as a girl are interlaced with chapters about her life as a mother of five. But elsewhere, the narrative feels jumbled merely to jack up suspense by endlessly postponing some essential revelation. I began to think of it as “Bridge of Delay.” The book’s elliptical structure self-consciously withholds information — names, meanings and motives; stray objects are introduced but not explained for hundreds of pages. These are tricks that Zusak simply doesn’t need to keep us engaged.

Around the world, “Bridge of Clay” is being released as a novel for adults, but in the United States it’s being published by Knopf Books for Young Readers, which gives me pause. Zusak has said he doesn’t worry about categories; he merely wanted to stay with the same staff at the U.S. imprint that brought out his 2005 blockbuster, “The Book Thief.” But how books are categorized, packaged and marketed does matter, and I hope this mature novel doesn’t end up boring teens without finding the older readers who will love it. Because overstuffed as it is, “Bridge of Clay” is one of those monumental books that can draw you across space and time into another family’s experience in the most profound way.

Ron Charles writes about books for The Washington Post and hosts

Bridge of Clay

By Markus Zusak

Knopf Books for Young Readers. 544 pp. $26.