Nestled on a well-kept block in the Potrero Hill neighborhood, the Koshkarian-DiFrancesco house looks like many of the 1930s houses on their street, complete with white trim and a traditional façade. “Remodeling wasn’t on our mind when we bought the house,” says Koshkarian, standing in her colorful living room with her eight-month-old, Zia, “but after a while, we realized the bedrooms were just too small and the closets were in different rooms. We were thinking of having a family, and if we had a child, we’d definitely need more space.” Koshkarian, a psychologist, and DiFrancesco, the CFO of a real estate company, wed in 2001, and bought the place the following year. “We really liked the location, the neighborhood, everything, except for the space issue,” says DiFrancesco. “We wanted to build up. We just didn’t know how hard it could be.”

After deciding they wanted an addition, Koshkarian solicited referrals from friends at California College of the Arts, her former employer. Though the couple had never renovated before, they both had a strong design sense, if not actually possessing technical skill. They needed to find someone who understood their vision and who could help realize it under budget. “It’s like choosing a new roommate,” jokes Koshkarian. Although the couple conducted the interviews alphabetically, Neal Schwartz, from the award-winning firm Schwartz and Architecture, surmounted his surname with a stellar resume and a genuine enthusiasm for the project.

Schwartz’s first order of business was to find out how much the homeowners wanted to match the style of the new master bedroom to that of the existing structure. Not much, it turned out. “I would drive around the neighborhood to see remodels,” says DiFrancesco, “They would carry the same ’30s style. I wasn’t interested in that.”

The architect couldn’t have been more pleased. “It was great to have clients be so supportive of a modern addition. They wanted to tie in the addition to the existing style but not replicate it,” adds Schwartz.

As construction began, so too came the inevitable, largely unexpected side effects of adding the third story. Decisions were made: where to put the staircase, how much work needed to be done to firm up the foundation, what kind of railing should snake up the entry into the master bedroom. The size and shape of the addition was determined partially by building-code requirements (anything more than 500 square feet would have required yet another staircase) and by neighborly concerns (including one incredibly close-by window). “We shifted the light to come over the [front of the] stairs,” says Schwartz. “In any organic system, [light] has a ripple effect that changes how you move through space.”

Ascending the new staircase, whose bamboo flooring was painstakingly matched to the hardwood of the original house, it’s clear you’ve hit new ground. The new master bedroom is showered with natural light by a series of eight-foot-high windows that open the addition to the outdoors, affording spectacular views of San Francisco’s skyline. The muted green and gray shades of the interior walls and siding create a sense of play between the public and private nature of the addition. “You feel like you’re both part of the city and apart from it,” notes Schwartz. The bed sits in the center of the room, framed from behind by a walnut-panelled wall that opens, in part, to a walk in closet.

The new addition shows the idiosyncratic touches that come from being able to design to one’s own specifications. “I insisted on this,” Koshkarian says, touching the small window above her desk, next to a computer. Schwartz, too, has his glory moments throughout the space, like the translucent medicine cabinet that doubles as the bathroom door. All parties agree that prioritizing the details in the master bedroom at the expense of, perhaps, redoing the foyer or straightening the downstairs hallway made for a more fully realized end product. “I would much rather reduce the scope of the project than the quality,” says Schwartz.

In the end, the hassles, the compromises, and the unforseen expenses of building another floor were worth it. The addition stands out from atop their very ordinary home without compromising the integrity of its context. “It’s a piece of my life that I’ve managed to do something creative and unique with,” says DiFrancesco. “It’s a reflection of us, our creativity,” echoes Koshkarian, reclining next to him. There is a pause before DiFrancesco says, chuckling, “I mean, I might not do it again. But I’m very glad we did it.”