When Simone Garreau and John Solit set out to expand their two-bedroom, circa-1936 Cape Cod–style home in northwest Washington, D.C., they didn’t want to overwhelm its modest character and scale.

“It’s this really cute, sweet, unpretentious, historic cottage,” Simone says—and they they especially loved the home’s tree house–like second story, with its steeply pitched roof and exposed, vaulted ceiling.

After: Backyard Annex

The couple had watched other houses in their neighborhood expand from charmers into behemoths, losing not only their architectural essence but also their rhythm of distinct, interconnected spaces in favor of open floor plans.

“A lot of architects told us, ‘This is what you do: You just take off the back of the house and you build onto it,’” Simone recalls. It would take a subtle balancing act to expand the home without going too large—or effacing its traditional details.

After: Backyard Annex

From the start, the busy professional couple knew that they needed a dedicated home office. They also sought to build a separate bathroom for their six-year-old son, Louis. While the existing home’s central dining room was ideal for entertaining, cooking from its tiny galley kitchen was not—and although they loved the atmosphere of the old Cape Cod, the interiors lacked natural light.

The couple reached out to architects Cooper Jones and Daniel Watson de Roux of Studio Bower, who agreed that the 1,985-square-foot house needed to expand the right way.

“The question became: ‘How do we respect the style of this Cape Cod, knowing the homeowners are modernists at heart?’” says Watson de Roux. “The breakthrough came when Cooper said, ‘Let’s make a modern cousin to the original house that continues the steep pitched roofline—on the second story, there’ll be that same ‘tree house’ experience they love in the current house.’”

“They fell in love with it,” continues Watson de Roux. “They said, ‘It’s like the house had a child—but it’s a modern child.’”

Before: Backyard

After: Backyard

Set in the home’s backyard, the new 900-square-foot annex features a kitchen and breakfast nook on the ground floor and a new primary bedroom upstairs. Though distinctly separate, it harmonizes with the original home with its nearly identical proportions, roof pitch, and material palette.

The annex has larger windows to let in more light, and an extended overhanging roof, which shades its exterior door. The bright ground-floor kitchen and breakfast nook offers floor-to-ceiling views into the leafy backyard; John’s father calls the space the orangery.

Since the annex’s second floor cantilevers over the patio, the edge of the glass wall could be built without a corner column. “The idea was to make the breakfast area feel like it’s right in the garden,” Jones says.

After: Breakfast Nook

Every surface along the back kitchen wall is painted British racing green; the clients told the architects to imagine a vintage Land Rover Defender. The cabinet detailing evokes the Georgian style (the forerunner of Cape Cod), but to keep things contemporary the cabinetry, backsplash, upper molding, refrigerator door, and the sides of the kitchen island are clad in the same material in a dark green tone. “We imagined the back of the kitchen as a single, green cabinet that’s been slid into place,” says Watson de Roux.

Before: Kitchen

After: Kitchen

The colored surfaces make the naturally stained wood countertops stand out. “Daniel brought in this beautiful cherry from a maker in Brooklyn,” Simone says. Together with the dark green cabinetry, the entire composition almost feels like furniture. “They pulled that off really well,” John says.

The new addition is connected to the original house with a glass-walled hallway that forms a transition between old and new. “It’s our cat’s favorite place to hang out because it really feels like you’re outside,” John says. “I didn’t fully appreciate it until I stepped into the space.”

After: Hallway

The homeowners don’t mind that their dining room is no longer adjacent to the kitchen. Instead, it’s around the corner, through the breezeway and a small multipurpose room (where the old kitchen was).

Not long after the family moved in, they hosted a fundraiser for 75 people. “It was the real proof of concept,” John says. “When we entertain, it feels like you can be anywhere in the house and you’re still part of the party, even though there are distinct rooms.”

Before: Primary Bedroom

After: Primary Bedroom

Then there’s the new primary bedroom above the kitchen, which is illuminated by a dormer window that’s larger than the home’s existing one, with an exterior shade that’s flat instead of pitched.

“We go to our bedroom a lot more now,” Simone says. “It feels really private, like this little tree house.” John agrees, saying “We did all this work, and I had no idea that my favorite place would be staring out this window.”

The firm also refreshed some portions of the original house, adding a new bathroom for the couple’s son. It’s completely wrapped in white tile, so the brightly colored toilet-paper dispenser, faucet, and vanity hardware pop. Watson de Roux drew design inspiration for the space from the 1992 movie Toys, starring Robin Williams.

Before: Upstairs Bathroom

After: Upstairs Bathroom

Simone and John approached the expansion cautiously—and they’re charmed by the transformation. “I never thought we would be able to do a project of this scale and be so invigorated by it,” Simone says. “We’re obsessed with this house, and we’re just really lucky people.”

More Before & After stories:

With a Crisp Addition, a Cookie-Cutter Eichler Breaks Out of Its Shell

Siblings Turn a Neglected Victorian Into a Dreamy Catskills Hotel

Their Brooklyn Limestone Was Trapped in the ’90s, so They Set It Free

Project Credits:

Architect of Record: Studio Bower / @studio.bower

Builder: Carl Petty Associates

Structural Engineer: Ehlert Bryan

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Before & After: They Loved Their Cozy Cottage, So They a Built an Annex to Match