Sometimes the only way to go is up—as was the case with this 1908 California builder’s cottage in San Francisco’s Castro neighborhood. Yet adding a third floor would have an undeniable impact not just on the house, but on the rest of the street.

The homeowners were fans of modernism, but were also keenly aware of the 1900s shingle-style vernacular that defines their block. Being mindful of the streetscape was crucial to the design; ignoring the past wasn’t a desirable option, nor was mimicking it. “You can’t get around the fact that cottages aren’t three-story buildings,” says architect Cary Bernstein, who knew her work was cut out for her: adding a third story to a building type that doesn’t have one, with adjustments in scale that made visual sense. Just as essential was introducing modern elements in a way that helps the façade “tell the story of layers of time,” says Bernstein.

Constraints abounded. The original two-story cottage was just 650 square feet on each floor, set back on a lot only 75 feet deep (most in San Francisco are 25 feet by 100 feet). Bernstein opted for the maximum allowable 500 square feet of space on the third-floor addition. Anything larger would require a second stair, which would hog what little usable space there was in the original structure. Adding onto the front of the house wasn’t feasible, given the tight lot, not to mention the tight budget. A rear stair wasn’t workable, either—the lot was too shallow and the budget was too small.

So Bernstein raised the roof while keeping its original pitch, designing a third floor made up of a master bedroom, master bath, and dressing area. She created a double-height stair hall that turned a dark cottage light and bright by moving the original first-floor entry closer to the sidewalk (the original front door had been set back in a cold, cramped exterior space that was not protected from the rain), making way for a light-filled entrance that now includes useful square footage on the interior.

The third floor’s window walls, which take full advantage of the spectacular city views, are intentionally designed to look different than the punched-wood openings of the original shell. Their black outline makes for a crisp façade that showcases the new and fuses it with the old. Offsetting the new parts brings geometry and contrast to the massing, turning a diminutive cottage with a quirky, chamfered façade into a sophisticated, unified structure.

Learn more about markets featured in this article: San Francisco, CA.