If you ask Carol Marra and Ken Yeh, a married couple of architects, where they put the heating and cooling machinery in their house in the Blue Mountains of Australia, a moment of confused silence may follow. And then a burst of laughter.
The 1,600-square-foot residence in the village of Leura, about 90 minutes west of Sydney, has no HVAC system to speak of. When temperatures drop in winter, the couple turn on a Dyson portable electric heater. When temperatures rise in the muggy, buggy summers, “We open a window,” Ms. Marra, 49, said.
Like many energy-efficient buildings, this one is physically oriented to make the most of ambient sunlight. But it is also thermally regulated by a secret sauce. Tucked between joists above the ceilings are packs of BioPCM, an engineered wax that melts as it absorbs heat when the interiors are sultry, and solidifies, releasing warmth, as the rooms turn cold. The low-tech, inexpensive wax is just one example of how the couple, who moved from the United States to Australia in 2002, squeeze efficiency and beauty out of materials and innovations.
Born in Malaysia, Mr. Keh, 53, was a competitive swimmer who was lured to the University of Texas at Austin by the size of its pool. He met Ms. Marra, an Argentine émigré raised in Texas, at the university’s school of architecture. After several years working in Seattle, they found themselves vacationing in Sydney for a few months before the 2000 Summer Olympics. The tidied-up host city had never looked better, and they decided to settle there.
Now, as principals of the Sydney-based firm Marra + Yeh Architects, they typically design buildings that are like birders, perched lightly and wide-eyed (or wide-windowed) in the landscape. This house, which sits at an altitude of about 3,000 feet at the base of a slope and is surrounded by trees and wildlife, floats on narrow steel pylons that are screwed into bedrock.
The minimally invasive foundation, a technology that was predominantly used in Australia to build solar farms and was adapted to residential construction, allows water to course uninhibited underground, filtered by the layers of sandstone into which the pylons are sunk. Above the surface, rainwater drains away without pooling. It is also collected from the roof in a large cistern.
“Our design literally goes with the flow,” Ms. Marra said.
In a way, the whole house goes with the flow, as it descends gently down the hillside, maximizing sunlight, views and cooling breezes with every vertical foot.
At the lowest level is the entrance, which opens to a long, rubber-floored mudroom where Ms. Marra and Mr. Yeh deposit their coats and boots after hiking one of the many local trails.
From there, they enter a living area that is anchored by an open kitchen, whose mosaic backsplash came about after they scooped up the last of a Venetian company’s green tiles at a tenth of the price. Lacking the necessary quantity, they mixed the green with much of what remained of the same tiles in purple.
“I was like, ‘Don’t throw it away. We’ll do something with it,’” Ms. Marra said. “And every single person that comes into this house is —”
“Mesmerized,” Mr. Yeh said.
The living room’s floor and ceiling are Australian eucalyptus plywood panels that serve as both structure and finish. The walls are gypsum and slathered with a paint into which sand was added to create a Venetian plaster-like surface.
“We’ve done away with having heavy materials within the building,” Mr. Yeh said, pointing out that their thermal system allows them to banish dense, albeit energy-efficient, concrete.
Off the living room is a deck with an outdoor kitchen, where Mr. Yeh cooks with a wok.
On the deck’s walls are another powerful signifier of their thrift-driven aesthetic: variegated planks of several different species of Australian hardwoods, plucked from the leftovers of timber mills and attractively pieced together.
The home’s single bathroom is above the main level and is sectioned into three areas covered in penny-round tiles in pointillistic shades of blue and black, like denim. The areas, which can be merged into a single space, are a toilet room, a wash area with a basin carved from a remnant of snowy marble with vivid black veins, and a bathing area.
In this last area, the shower is next to a large window looking out to a green panorama (the house sits on about half an acre), but not to any neighbors. “It’s like an outdoor shower without being outdoors,” Mr. Yeh said. There is also a Japanese-inspired collapsible bathtub that the couple designed, using a knot-filled piece of Canadian cedar.
“In a way, we are pragmatists,” he said. According to the architects, the cost of building and furnishing the home was about $400 per square foot.
At the home’s topmost level are the couple’s bedroom and their satellite architectural office. A library attached to the office doubles as a second bedroom; a deep closet there was specially designed to hold a futon that can be unrolled for guests.
But as inviting as this house is, it was built defensively. For decades, the Greater Blue Mountains Area, a UNESCO World Heritage site, has had devastating wildfires. The most recent, which burned more than two million acres from September 2019 to early 2020, coincided with the construction of this property.
Ms. Marra and Mr. Yeh took several measures to mitigate fire exposure. They started by placing the house at the base of the slope, at a distance from their neighbors and with ready access to emergency services.
The steel structure is coated in intumescent paint more commonly used in commercial buildings; it “bubbles up” under high temperatures, as the couple described it, creating a protective sheath around the metal.
The cistern supplies water for a sprinkler system designed to soak the building’s exterior to prevent flying embers from igniting it.
All of these strategies double as educational tools, as do the scrappily artistic design choices that permeate the home. When Mr. Keh is teaching architecture studio classes, he said, “I tell my students, ‘If you guys behave and do really good work, then you’re invited to come to my house.’”
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