When BK Lin asked architect Melissa Shin to design an ADU for her home in Mountain View, California, she had no idea a worldwide pandemic was on the horizon. The project, which they initially expected to take a year or two, took four instead.

The upside? The client and architect became close friends over those four years, which enhanced Shin’s vision for the design. With two square 16-by-16-foot volumes (one public and one private), plenty of sunlight, and brilliant pops of pink and green, the resulting ADU lives larger than its approximately 500 square feet.

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BK first considered adding an ADU to her property in 2016. The large lot has a duplex—the tech-industry executive lives in one unit and rents out the other—with a sizable yard behind it. “I’d been reading a lot about ADUs and had this big empty yard,” she says. “I thought it would be a great to add more long-term income to the property, but in a way that wouldn’t require me to disturb or change the front units.”

BK immediately thought of Shin for the project, as the architect’s former firm designed a few projects for BK’s company in 2015. “We always kept in touch,” says BK. “Years later when Melissa told me she was starting her own office and would mostly be working on ADUs, I thought my ADU would be a great collaboration!”

$9,400 Site Prep	$32,000 Foundation	$55,500 Framing
$7,000 Roof, Gutters, & Site Drainage	$6,350 Doors & Windows	$15,250 HVAC System
$11,400 Stucco & Fire Protection	$10,000 Exterior Plumbing & Trench	$12,000 Interior Plumbing
$18,000 Electrical	$4,500 Insulation	$10,500 Drywall
$15,770 Millwork	$900 Hardware	$4,720 Counters (Labor & Materials)
$1,750 Trim	$1,800 Baseboard	$7,500 Paint (Interior & Exterior)
$15,150 Tile (Labor & Materials)	$6,450 Plumbing Fixtures	$1,700 Lighting Fixtures
$1,900 Water Heater & Vent	$2,200 Shower Door	$5,980 Flooring (Labor & Materials)
$1,500 Low Voltage	$7,000 Solar
Grand Total: $266,220

When they began planning the design in 2018, BK knew she wanted a separate bedroom and a full kitchen and bathroom. “I didn’t want something with mini-size appliances,” she says. “I wanted it to look and feel like a house.”

Then Shin discovered the property had r-2 zoning, which prohibited ADUs at the time. “I’d heard rumblings of pending legislation that would change restrictions,” says Shin—so they briefly tabled planning, and they were able to proceed when the law changed a few months later. “Because it was so new, it was incredibly difficult to get through planning approval and plan check,” explains Shin. “And as soon as we were approved for the permit, Covid hit and the project had to pause.”

In 2022—three and a half years after Shin and BK began—the pandemic eased and they were able to start construction. “The general contractor was skilled, but flaky and super unorganized,” says BK. “Since we were three years into the process, I really wanted to move things along.”

“BK spearheaded on-site management since I’m based in Los Angeles and couldn’t be as hands-on as I normally am,” says Shin. “We quickly built a lot of trust and a stronger friendship.”

“This project was my office’s first commission, but by the time we finished, it was our fifth completed project and our third ADU,” Shin explains. “Every time I picked the project back up, I’d tweak small things in the design after learning something from another project or having renewed clarity from seeing the project again with fresh eyes.”

All told, the ADU cost $266,220 to construct. Shin and BK sought out budget-friendly exterior finishes—like asphalt shingles for the gable roof, which cost $7K including gutters and site drainage, and fire-protected white stucco walls for $11,400. To lend richness, she accented the stucco with a vivid shade of pink for the front door and the fascia.

The team splurged on the interior, where they spent $15,770 on custom millwork and $15,150 on tile for the kitchen and bathroom. In the open-plan public volume, Shin arranged a large kitchen, a dining space, and a living area. Olive-green Fireclay tile and verdant lower cabinetry anchor the volume, lending interest and vibrancy. “The tile changes throughout the day,” says Shin. “It can read as very neutral in daylight and it becomes more saturated with artificial light.”

Per BK’s request, Shin packed a sizable bedroom, a full bathroom and shower, a walk-in closet, a stacked washer and dryer, and as much built-in storage as possible into the private volume.

“The floor plan is diagrammatically simple,” says Shin. “The two 16-square-foot squares are joined along a center axis with a single door that connects them.” Shin aligned the doors and windows along the east-west axis. “At just the right time in the morning, you see the sun rising through the eastern bedroom window and stretching all the way through to the living space, where you see the sunset.”

The living area has a 12-foot vaulted ceiling, while the bedroom has a 9.5-foot flat ceiling. “You feel a shift in intimacy between the squares as the ceiling height changes,” says the architect. “It’s a basic architectural idea of compression and expansion that’s effective, even at this scale. This is our office’s smallest project, yet the proportions make it feel much larger.”

BK couldn’t agree more. “Every detail is clean and meticulous, making the space feel big,” she says. “This is also the feedback I’ve gotten from potential renters, and it’s pretty much been rented from the day we finished construction until now.”

“I see the design as one instance of a much larger strategy for providing additional housing on existing multifamily properties,” says Shin. “As legislation to address the housing crisis evolves through SB9 and AB 1033, this scenario of having three units on a standard lot is an example of how densification can be realized by the typical homeowner on a limited budget.”

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In a move to control the budget, Shin and BK pumped the brakes on adding an outdoor dining terrace that connects to the living area. “The private dining patio with landscape features for the west side of the ADU got value engineered out of the project,” says Shin. “BK will eventually finish the full vision for the site, but for now those plans are on hold until she recoups some of the costs and reevaluates her vision for the rest of the yard.”

BK is also reconsidering her future plans for the ADU itself. “In the back of my mind, I think I could rent out both of the duplex units and [eventually] live in the ADU,” she says.

More Budget Breakdown stories:

She Built a $277K Starter Home in Her Childhood Backyard

His $11K Backyard Office Has Worktops Made From a Tree Planted by His Grandfather

With $89K, an Architect Expands His L.A. Home for Three Generations of Family

Project Credits:

Architecture: Shin Shin Architecture / @shinshinarch

Structural Engineer: Paul Boranian

T24 Consultant: Sheer Energy

Vase: Voyage Decor / @voyage.decor