By the end of the aughts, Molly Alexander and Graeme Anthony were getting restless in the Victorian that they had owned since their 20s in Montreal’s lively Plateau neighborhood. Their son, Max, was five, and Alexander says she had grown “tired of having drunks lying on my stoop and yelling at three o’clock in the morning. I was like, ‘I’m over this.’”

The couple had long entertained a fantasy of buying a multiunit building in La Petite-Patrie—a gentrifying, formerly working-class neighborhood northwest of downtown, where Alexander had grown up—and renovating it into a spacious family home. One Saturday in 2009, they visited Alexander’s childhood home, where her mother, Patricia, still lived, and saw a For Sale sign on an unremarkable four-unit building next door.

They put in a bid the next day, despite what Alexander encountered when she went inside: a warren of light-starved rooms and a series of questionable decorating choices, including a hot-pink wall and garish artificial grass on an upstairs balcony. A series of cheap renovations had stripped the building, which dates to the 1920s, of any period charm, making it easy for the couple to gut the inside and start from scratch. “We didn’t say, ‘Oh, maybe we’ll keep a wooden beam,’” says Alexander, a union organizer. “The idea was: The uglier, the better; the cheaper I can get it, the better—because I wanted to rip it down.”

Alexander and Anthony, the manager and shoe buyer at a men’s streetwear clothing store called Off the Hook, wasted little time finding the right architect. Anthony recalled taking Max to a birthday party at the renovated home of Alexandre Blouin, a founder of the Montreal firm Blouin Tardif, and being impressed with how the architect had opened up an older structure. “I don’t think we even talked about hiring anybody else,” Anthony says.

Blouin designed a rectangular staircase at the center of the house, positioning it beneath an operable skylight that draws in sunshine that otherwise would have struggled to penetrate the core of the building, which is 50 feet deep. The kitchen was moved from the rear of the house closer to the middle, freeing up space at the back for a new sitting room and a set of floor-to-ceiling windows.

A shallow crawl space beneath the house was excavated and turned into a finished basement, with a new family room and a door that opens onto a patio where a driveway used to be. A steel footbridge provides direct access to the main level from the garden.

The renovation, executed while Alexander was pregnant with the couple’s second child, took about nine months and was completed in the summer of 2011. Alexander and Anthony share a generously sized master suite at the back of the second floor, while Max, 11, and Chloe, five, each have a room at the front, with a shared balcony.

Signs of happy children at play abound—but more in the form of errant toys than paint colors or permanent architectural features. “I was very conscious when we were designing the house to not design it for children,” Anthony says, “because 10 years from now they’re not going to be kids.”

The decision to design with the future in mind makes the house a flexible space that Alexander and Anthony conceived as a landing spot for the long term. “I wanted to live in a place where I could get old,” Alexander says. “When the kids are teenagers, the house works for that. The kids move out, I can still live here. The idea was: The place is ours regardless of how life changes.”