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In Mill Valley, California, where driveways are highly prized and every square foot counts, having an ADU in the backyard is like winning the jackpot. So when a family of five tasked designer Anja Michals with rethinking the dated cottage behind their Craftsman-style home, she leaned all the way in, gutting the structure, connecting it to the main residence (via a cheerful new mudroom), and transforming it into a colorful, pattern-packed retreat. Now, it’s part guesthouse, part office, part bunk room, and part kids’ hangout.
Completed earlier this year, the 980-square-foot addition is the happiest spot in the house. “The idea was to have a super eclectic, vintage-inspired space,” says Michals, who teamed up with architect Heidi Richardson on the project. And because the clients were longtime collaborators, they weren’t afraid to take some risks.
The first clue that this isn’t your average house extension is in the mudroom, where ochre-yellow cabinetry and checkerboard tile greet you. Rather than hiding utility spaces, Michals prefers to make them part of a home’s story; the adjacent laundry room has no shortage of wallpaper, paint, and millwork despite its compact footprint.
The transitional spaces were also design opportunities in Michals’ eyes. A narrow hallway connecting two rooms became one of the home’s standout moments thanks to a bold cameo wallpaper. “Everywhere you turn there’s a different fabric or pattern,” Michals explains. Switching up the scale of neighboring prints, but repeating colors (here, terracotta) was the key to making it all feel cohesive instead of chaotic.
Inspired by a hotel stay in Mallorca that left an impression on the family, the bathroom is wrapped in stripes upon stripes: on the backsplash, the floors, and the shower stall. But of course, that’s not the only motif—Delft-style floral tiles are tucked throughout like little surprise gifts.
Another valuable deign lesson comes by way of the petite office lounge. Michals put built-ins to work on every available wall, squeezing in floor-to-ceiling shelving, a built-in desk, and a cushioned daybed for overnight guests with storage underneath. “I love designing small spaces,” she says. “You really have to get creative.”
Notably absent? A kitchenette. Because the former ADU is now physically connected to the main house, the family prioritized comfort and breathing room over creating a completely independent suite. To help the addition feel intentional rather than tacked on, the team looked to the home’s existing arches to inspire new ones throughout the structure, and added architectural accents like wainscoting and exposed beams. “All those little details really make a difference when you’re in a small space,” Michals notes.
No room is rigid in its purpose. One son has already claimed the green bunk room as his permanent bedroom, while the rest of the extension flexes depending on the family’s everyday needs. In this case, an ADU can be far more than just a guesthouse; it can be a staycation for the entire family.
