An architect’s colorful family home stands out in Brooklyn

On the rooftop of a converted rowhouse in Greenpoint, Brooklyn, Sophie and Lila Drouin can often be found running around a wooden deck ringed by potted plants and, if the weather warrants it, splashing each other while playing in a fold-out children's pool.

The sisters love rambling around the 300-square-foot terrace on top of their home, tracking the growth of the family’s vegetable garden (tomatoes, strawberries, and even potatoes from Colombia, where their mother, Martha Escobar, was born), marveling at the movement inside the compost pile (what kid can resist worms?), and taking in the panoramic view of the New York City skyline.

"This space is very small, but it changes how we use the house," says their father, Serge Drouin, a French architect with Renzo Piano Building Workshop and grandson of famed French industrial designer Jean Prouvé, who designed and helped remodel the three-story building where his family now lives, in collaboration with another family that shares the lower half of the building. "I will eventually have a desk here on the top floor. I’ll either work from home a lot, or watch the view and not get a lot of work done."

Hearing Drouin—who moved into the space with his wife and two children last May—talk about their home as his daughters run in circles behind him brings the before and after contrast into even starker focus. Though today it features an airy, colorful interior, the residence, built in 1901, was a wreck when Drouin and the future co-owners came across it two-and-a-half years ago. The house was little more than a decrepit shell pockmarked with damage, decay, and the byproducts of animals run amok.

Sweat equity in this case meant spending part of his paternity leave scraping out the dank interior. "It was definitely a challenge," he says. "It’s a big adventure to take on such a task." But Drouin didn't merely rebuild, he redesigned, embarking on a small experiment in making family living in the city more affordable.

Like many buyers looking for a home in New York City, Drouin and Escobar, a speech therapist, were heads of a growing family challenged by the city’s rapidly rising real estate prices. While living in Greenpoint and considering the high asking prices and expansive renovations that often came with acquiring a single-family home, Drouin hit upon an idea: Instead of trying to find a building they could afford by themselves, or settle for a cookie-cutter condo which offered a cramped and inflexible living space, why not create their own third option?

They could go in with another family and split a three-story house, reducing the cost of acquisition, while Drouin drafted and designed a new layout for the 2,750-square-foot building, giving each family a floor-and-a-half of well-proportioned space. The resulting split, which finds his family taking the top section while their neighbors live downstairs, draws inspiration from Le Corbusier’s idea for interlocking duplexes of a floor-and-a-half, which he demonstrated at the "Unité d'habitation" in Marseille, applying them the formerly cramped quarters.

Drouin designed the entire building, and helped build out the entire home. The families have joint ownership of the space—Drouin calls the arrangement a bit of a "neighbor prenup—but what freedom they may have given up with joint ownership of the building, they gained with the ability to design a custom home for their family ("it’s a win-win").

"People often design their homes thinking about what adds value," Drouin says. "But I think it’s more about figuring out what makes the space comfortable and more personal and specific. In our apartment, it feels as if we have the same amount of space as other such buildings on the block, even though two families live in the same building."

Drouin served as both architect and contractor during the year-long gut rehab, managing construction and keeping the tight budget in line. Minus a few minor issues with sound separation between the units, both families have been happy with the results.

After entering the Drouins' 1,350-square-foot home through an eye-catching lime-green door that contrasts with the building's corrugated aluminum facade, guests first encounter the combined living and dining room. Its clean, open floorplan helps maximize gathering space for the family, and it features a low storage unit that runs along an exposed-brick wall, ending at the crisp, white kitchen with built-in cabinetry on its back wall.

A bevy of books in multiple languages can be found on the floor (during daily conversations, the family can switch fluently between French, Spanish, and English). Stripping down the walls and simplifying the layout makes the home's 18-foot width seem even more spacious. A selection of bright furniture and decorative objects—including an orange Eames rocker and George Nelson clock—provide pops of color amid the understated decor. The assortment of chairs around the sleek dining room table, a grab bag of pieces by Jean Prouvé, pays tribute to Drouin’s grandfather.

"We have three different atmospheres in the house," says Escobar. "On the first floor, we really only go there to cook and eat. The second level we play and can make a mess, and then we have the outdoor space on the roof." A flight of stairs to the left of the kitchen leads to the second floor, which contains the family’s three bedrooms, linked by a hallway that doubles as a living room and play space for Sophie and Lila.

Drouin’s space-saving design really shines in this section of the house, which benefits from the added light that streams in from an additional stairway that leads towards what was once a cramped attic. Storage units built into the walls reduce clutter, and the kids' two bedrooms, built against the back wall, were designed to grow with them. Lofted spaces now used for storage can be converted into beds, allowing the girls the opportunity to redesign their rooms when they are older. Escobar loves how this floor is functional and adaptable without wasting space, making the most of the 18-foot-wide lot.

"It's great because we can change the bedrooms as they grow," she says. "They have the same amount of space, and can't fight about who has the bigger closet." With the hallway often serving as a hive of activity, the master bedroom gives Serge and Martha a clear view of the rest of the floor. Set behind a glass wall, the room often provokes questions about parental privacy. Drouin says they’ve adjusted to the openness, and besides, the glass wall gives them the added benefit of a natural alarm clock. Pointing up the stairs that lead to the rooftop, he shows the window that allows the sun to shine into the room every morning.

The only downside is having to occasionally clean off the handprints left by their children. "Lay down here on the bed, and you have the view of the sky and the clouds," he says. "At night, the window frames the moon, and it looks like a picture." Maintaining the subdued vibe, the master suite contains a painting of Drouin’s grandfather, as well as a colorful painting above the bed done by Drouin and Escobar that could be mistaken for a Rothko. Another stairwell leads back to the roof.

Drouin designed the home to channel hot air into the bulkhead-like space atop the home, to help with circulation and vent the home when it’s too warm. A fan recirculates the warm air during the winter to cut down on energy costs. It’s part of a series of "simple tricks" the architect used to naturally heat and cool the home.

Drouin feels the building’s layout can offer a sustainable model for urban development, offering more space for families without completely sacrificing density. Being concise with limited square footage gives the family perhaps the ultimate luxury in a big city; a feeling of openness and space.

Upstairs on the roof, the family often gathers for dinner around a red fold-out table Drouin acquired at a flea market in France. While the other family in the building has its own outdoor space, a garden in the backyard ideal for afternoon barbecues, Drouin loves the family’s perch "When you go out, you have a view of New York that you don’t expect to find here," he says. "On the top of the home, we feel a bit like we’re in the countryside."