Mark Arnold had owned a few different homes in Los Angeles and Palm Springs, but none of them fulfilled a dream he had harbored since childhood. “I always wanted to build my own house,” he said.

Mr. Arnold, 62, a critical-care nurse with a keen interest in architecture and design, relished the idea of building a modernist structure that reflected his taste and his ideas about how to live well. Specifically, he wasn’t interested in living in a big house full of empty rooms he wouldn’t use.

“I wanted a small, architectural house,” he said. “Just for one person.”

When he read an article about a small house on a tiny lot in the Echo Park neighborhood of Los Angeles that Simon Storey, the architect who founded Anonymous Architects, designed for himself, he sensed that he had found the ideal collaborator. Upon meeting Mr. Storey, his instincts were confirmed.

“We hit it off right away,” Mr. Arnold said. “He totally understood the kinds of concepts I was thinking about.”

With an architect selected, there was just one more hurdle — but it was a significant one: finding a lot in Los Angeles that he could afford. He looked in Silver Lake and Echo Park, but had no luck. Then he heard about an unusual spot in Mount Washington. When he drove out to see it, he had a hard time finding it. The land was so steep, he said, “it was just a guardrail and a cliff.”

But the view over the city was breathtaking. And when Mr. Arnold crept up to the edge of the 0.15-acre lot, he could see that it wasn’t actually a cliff. There was land below, but the hillside fell away like a black-diamond ski run.

He asked Mr. Storey to take a look, and the architect deemed the site a good buy. “Obviously, it’s incredibly steep,” Mr. Storey said. “But steepness doesn’t necessarily mean it’s not buildable. What makes it buildable is the geology. And we’re pretty fortunate in L.A. to have really steep lots that are actually pretty healthy below the surface.”

Mr. Arnold bought it for $45,000 in July 2013, and Mr. Storey got to work on the design. The architect conceived plans that called for a small garage at street level; a staircase down to the roof of the house, which would serve as an outdoor patio; and 975 square feet of living space below that.

Although the home is small, Mr. Storey maximized the size by pushing the footprint out to the required setbacks from the lot lines. “You don’t have the luxury of endless square footage,” he said. “So you need to capture the square footage you do have and make it do as much as possible.”

The resulting house, which is built around retaining walls that sit atop concrete piles extending deep into the earth, has a shapeshifting interior that can be changed by moving the sliding wall panels. When the panels are tucked away, the house feels almost like a loft, with open sightlines between the living room, primary bedroom and den. If guests are coming over and Mr. Arnold doesn’t want his bedroom on display, one of the panels slides out to close it off. If a guest will be staying overnight in the den, which is equipped with a discreet Murphy bed, two more panels slide out to create a wall between it and the kitchen, while a third panel separates it from the bedroom.

In the compact bedroom, “everything is built in,” Mr. Arnold said, including a wardrobe wall with drawers and hanging space behind the doors, drawers under the bed and wall-mounted night stands. “I don’t have big walk-in closets and stuff like that, but there’s plenty of storage because we’re doing it in a smarter way.”

One of the most unexpected features of the home is the slender pool that Mr. Storey tucked between the house and the hillside, accessible from the roof. From underwater, it’s possible to peer into the house through a window in the back wall of the kitchen.

To finish the interior, Mr. Arnold worked with Sarah Rosenhaus, a friend and interior designer. “He really wanted to create warmth within this amazing, supermodern structure they were building,” Ms. Rosenhaus said.

To do that, she and Mr. Arnold found vintage Brazilian and midcentury-modern furniture, including a Jangada lounge chair by Jean Gillon that was given pride of place in the living room.

“We also looked to bring in color by giving each distinct space its own palette, even though it’s one big, open room,” Ms. Rosenhaus said.

In the bedroom, they chose a bed with a plum-colored headboard and salmon-colored bedspread. In the den, they installed a custom sofa upholstered in rust-hued corduroy velvet. For the living room, they selected an off-white rug and linen-covered daybed to let the green of Mr. Arnold’s houseplants shine.

None of it happened quickly, or inexpensively. After he bought the property, it took Mr. Arnold years to get the permits necessary for construction, which began in September 2017. Then the approval for a septic system was revoked, and Mr. Arnold had to pay to extend the public sewer to his property instead.

Just as the project was nearing completion, the pandemic struck. Mr. Arnold was overwhelmed at work, stuck in a rental apartment and unable to get the certificate of occupancy he needed to move into his new home. “We couldn’t get inspectors to inspect,” he said. “I was in the nightmare of Covid here, having to pay the house payment, my rent and all these extra costs for the house.”

The only silver lining was that Mr. Arnold could work as much overtime as he wanted, because nurses were in such high demand. “If I needed some money for the house,” he said, “I could just work more.”

In December 2020, he finally got approval to move in. Although he had budgeted about $700,000 for the project, the total cost ended up being more than $1.1 million, much of which he paid for with a construction loan.

Nevertheless, Mr. Arnold is confident that it was a good investment. “I don’t think you could get a house for $1.1 million anywhere in L.A. now,” he said.

And more important, the home represents the realization of a lifelong dream.

“I made this,” he said. “That’s sort of unbelievable to think about. The house is amazing, and I just love living here.”

Living Small is a biweekly column exploring what it takes to lead a simpler, more sustainable or more compact life.

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