When Naomi Sachs and James Westwater first decided to trade Santa Fe, New Mexico, for the art scene in Beacon, New York, they envisioned finding a bucolic piece of land on which to build a house. A small, über-modern, eco-friendly prefab house much like the subcompact architecture that artist Westwater explores in his installations.

But when they got to Beacon, they fell in love with a huge gymnasium.

“Our Realtor emailed over photos of this cute little red brick building in Beacon,” says Sachs, a landscape architect. “We got here and realized that it isn’t small at all! But at that point, we were already seduced.” The 5,000-square-foot “Gymnasium and Drill Hall” was built in 1900 for a boys boarding school called the Beacon Military Academy and, during World War II, was turned into an electric motor factory. Despite its size, Sachs and Westwater bought it in June 2005 and kicked off three years of renovations by having the place gutted. “We moved into this huge shell with just a makeshift kitchen and a dingy basement bathroom,” Sachs remembers. “The construction happened in stages from there, so we kept moving our bed and the kitchen around to whichever corner of the house wasn’t being worked on.”

The couple hired architect Aryeh Siegel to design and draw up plans, but they did much of the labor themselves—from installing the kitchen to restoring and weatherizing doors and windows—with Westwater serving as general contractor. They cite several sources of inspiration for their renovation, including the neighboring modern art museum, Dia, which opened in 2003 in a converted Nabisco box-printing factory, and the pair of Victorian warehouses that Westwater’s father, an architect and industrial engineer, turned into the family’s home when Westwater was growing up in Lavenham, England.

Alongside these grand, industrial spaces, the couple continued to study books on prefab houses. “People always think it’s funny that we’ve ended up in this huge space when we own at least 10 books on living in small spaces,” Sachs says. “The books did inform what we wanted to do with this house, which was to create smaller, more intimate spaces within this big open structure.” While the main room serves as an expansive kitchen and living room that bleeds over into Westwater’s art studio, the loft above features a cozy den-style sitting area where the couple can watch movies with their dogs.

One particularly petite space was very important during the early phase of the renovation: The couple built a tiny freestanding studio/office for Sachs in their back garden. Once complete, the 120-square-foot “Little House” became home for six months while the inside of the gymnasium was uninhabitable. “We could cook and use the bathroom inside the house, but that was it, so it was the two of us, our three dogs, and a king-size bed out there,” Westwater says. Sachs planned the structure around a pair of large sliding glass doors and windows, so the couple woke up each morning to a view of the rain garden she designed.

As the founder of the Therapeutic Landscapes Network, Sachs studies the restorative benefits of nature and was eager to soften the institutional home with greenery. “We also knew that improper water drainage is a huge problem in Beacon and that our basement would get wet every time it rained if we didn’t do something,” she explains. “I chose to make a rain garden because it creates a use for the water here on our property rather than letting it flood our downhill neighbors.” Underground pipes collect and funnel storm runoff from the house so it emerges via a stone fountain to feed a collection of serviceberry trees that stand in gravel mulch. The spare landscape evokes the couple’s beloved New Mexico. “I had planned to add a layer of ornamental grass, but it seemed like too much,” Sachs says. “It sounds terrible, but I actually ended up feeling a little sad when it was finally time to move into the big house.”

Inside, the couple’s aesthetic remains what Sachs calls “a kinder, gentler minimalism,” in harmony with the beautifully preserved historical elements. “Of course, once you decide it’s about respecting the space, then you’re faced with—respecting the space,” Sachs says with a laugh. “And in this case, the house was quite bossy. We had to figure out how to work inside all the geometric windows and beams.” Pairing white walls with exposed wood and stainless-steel counters created a light backdrop for their constantly evolving collection of artwork and vintage furnishings. Here, too, their small space ethos serves the big house well: “I have no problem getting rid of things,” explains Westwater. “The key to minimalist living is an eBay account in good standing.”

Sachs is quick to point out that clever storage helps too. “Probably our one bone of contention is that I’d love to be surrounded by lots and lots of books, but somehow when books compete with art for wall space, the art always wins,” she says. Maybe now that they have so much space to work with, books, which have been tidily tucked away downstairs, might find their way into the decor? “I’d be OK with piles of books,” concedes Westwater, “but only in sculptural piles.”

A Few of Their Favorite Things.

Gaggenau oven and cast-iron tub from Green Demolitions, which sells commercial surplus and donated kitchen fixtures, appliances, and building materials at 50 to 90 percent off their retail prices. Proceeds support Recovery Unlimited, a nonprofit that provides outreach services for All Addicts Anonymous.

Concrete bathroom counters and bathtub from Betonas. A custom-made stainless-steel kitchen counter made at a shop in Brooklyn.

Oversize midcentury velvet-like sofa from favorite local antique store Relic (845.440.0248).

A collection of thrift store paintings (original artists unknown) to which Westwater added his signature hard-edged geometric shape in an “unauthorized collaboration,” he says. “I like to collect thrift store art that’s right on the cusp between good and bad.”

Windows and sliding glass door on the “Little House” from Hudson Valley Materials Exchange, a local nonprofit that sells reusable building waste otherwise destined for landfills.

To see how to make your own built-in storage like Westwater and Sachs', click here.