Standing inside the 1,000-square-foot ADU in Fairfax that Nick and Sylvia Calder now call home, it’s immediately apparent that this is no ordinary residential structure. The walls are far more substantial than a typical home’s — 22 inches thick, to be exact — and made of concrete covered in natural plaster that feels softly textured to the touch. Nick, a contractor by trade, built the structure himself after spending years researching concrete construction systems. “I’ve had a dream of building a concrete house for probably 20 years,” he says.
A native of England, Nick arrived in Marin 35 years ago by way of the Panama Canal, having sailed here from Wales, with a two-year pitstop in the Caribbean, on a small sailboat. He never intended to stay, but it took him longer than he expected to sell his classic wooden sailboat — years longer. In the meantime, he got married and had kids. Eventually, he bought a rundown 1920s-era home in Fairfax with the intention to fix it up, sell it and move on. As time went by, however, he decided to stay, making many improvements to the property over the years, including transforming the backyard into a lush, tropical oasis with a swimming pool.
A few years ago, when Nick was getting ready to retire, he and his wife, Sylvia, decided to build an ADU on the property overlooking the pool where they could age in place while deriving rental income from the primary residence. He hoped to build a structure that was in some way reminiscent of his childhood home back in Europe. “My parents’ house had huge, thick stone walls and windowsills that you could sit inside and look out to the ocean,” he says. “I wanted a house like that.”
Aesthetics weren’t the only reason Nick wanted to build a concrete home. He was also concerned about wildfires. Soon after he bought the Fairfax property, he attended a community meeting called by the local fire chief, who informed him about the risk of wildfire in the area, a heavily wooded valley about a mile away from downtown Fairfax with only one road in and out.
“He said, ‘Your street is particularly dangerous; it’s high fuel with a lot of trees and houses and given a certain set of circumstances like wind direction and windspeed, we wouldn’t attempt to fight a fire on your street,’” Nick recalls. Given the risk, Nick reasoned, concrete seemed like the most suitable modern building material for constructing a home. “Over the years, we’ve thought about how to stay alive if we got stuck here,” he says, “and all the things that destroy wooden buildings — fires, tornadoes, floods, dry rot, termites, storms — concrete is pretty immune to.”
After researching options, Nick found that the patented Energy Mass wall system from Emeryville-based Integrated Structures met all the criteria he was looking for. Energy Mass walls are built on site, constructed with an insulated foam core surrounded by two skins of 3-inch-thick shotcrete (sprayed concrete). The walls’ highly insulated design promotes energy efficiency and dampens sound. Most important, however, the walls are extremely resistant to fire, even surpassing California’s Chapter 7A building codes, says R. Gary Black, chief designer and president of Integrated Structures and professor emeritus of architecture at UC Berkeley. “A typical residence burns in about 20 minutes, and the code stops counting at four hours; these walls are rated for four and a half hours,” he says. To date, Black shares, two residential structures built with Energy Mass walls have been engulfed in wildfires — the 2017 Tubbs Fire and the 2020 LNU Lightning Complex fire — and survived unscathed.
When Nick was ready to start the project, Integrated Structures designed and engineered the building with Energy Mass walls; a poured-concrete roof; and double-paned, tempered glass windows. They also created a 3D model to show Nick and Sylvia how the ADU would be sited on their sloping property in relation to the primary residence, garage and pool. With guidance from Integrated Structures, Nick and his crew started construction and a year later, the one-bedroom, one-and-a-half-bathroom detached ADU was finished. “It inevitably took us longer since we were learning a new system,” he says. “It’s a totally different type of construction.”
To lend an old-world Mediterranean feel to the building’s exterior, Nick applied a warm, neutral, color-coated natural plaster finish to the concrete. He also installed bi-folding doors that open from the common space to the pool deck, as well as wooden rafter tails under the eaves of the roof. “The rafter tails are superficial and don’t form any part of the structure, so if there’s a fire and they were to burn off, it wouldn’t have any impact,” he explains.
Inside, 11-foot ceilings in the combined living, dining and kitchen area make the compact dwelling feel larger than it really is. Up a short flight of stairs, where the primary entrance is located, the bedroom and en suite bathroom feature plenty of built-in storage. Throughout, features like the walk-in shower and low-rise steps were designed with aging in place in mind.
Like the exterior, Nick incorporated traditional European details into the interior spaces, including custom metalwork; a thick-walled, arched doorway to the bedroom; arched windows between the bedroom and living area that flood the spaces with light; and decorative wood ceiling beams. With the wood leftover from the beams, he even crafted a large dining table and bench for hosting family dinners.
Radiant heating is integrated into the concrete flooring, which Nick and Sylvia finished themselves using an acid stain and epoxy coating. “It was a huge cost savings for us to do the floors ourselves,” Sylvia says. “We just love how they came out. They’re easy to maintain and impervious to dogs and the grandkids running around.”
Now retired and living full-time in their ADU, Nick and Sylvia couldn’t be happier with the way their home turned out, from the look and feel of the structure to the fire-resistant design to the consistent year-round indoor temperature. With the fires in Los Angeles earlier this year tragically destroying upwards of 10,000 homes, Nick hopes others will consider building with concrete.
“When the fires happened in Southern California, I called Gary and said, ‘When are people going to realize that building out of wood doesn’t make sense?’” he says. “I’m a real advocate for this type of building.”
Lotus Abrams has covered everything from beauty to business to tech in her editorial career, but it might be writing about her native Bay Area that inspires her most. She lives with her husband and two daughters in the San Francisco Peninsula, where they enjoy spending time outdoors at the area’s many open spaces protected and preserved by her favorite local nonprofit, the Peninsula Open Space Trust.