How to build a home to withstand floods and fires

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Carol Marra and Ken Yeh have years of experience designing climate-resilient houses for others, but their 150-square-metre new home – their first for themselves – on a steep Blue Mountains block in a bushfire zone, with a hanging swamp underneath, tested their mettle.

“Worst clients ever,” said Marra, an architect.

The couple wanted to future-proof their home by building to a higher fire rating than required for their site; prevent water damage from the sheets of rain they’ve seen coming down the hill in deluges; and restore the site’s flora and the fragile hanging swamp running below.

Carol Marra and Ken Yeh at their Eco House, in the Blue Mountains.

“Fire and floods. That is what Australia is about every summer, yet too few of our homes are built to withstand a climate emergency,” said Marra, who won a Churchill Fellowship on passive design to accommodate severe climate patterns.

For the couple, the founders of Marra + Yeh architectural practice, the solution was to go with the flow, and work with the site’s natural attributes rather than try to conquer them.

UTS Professor Elizabeth Mossop, academic director of Living Lab Northern Rivers, said Australians had “not got our heads around the fact that floods and fires are now situation normal”.

Governments spend 97 per cent of resources post-disaster and three per cent on adaptation to mitigate the impact of climate disasters, Mossop said.

The Eco House was designed to survive Australia’s tough climate.

Researchers were now trying to “switch the spending from post-disaster to pre-disaster because every dollar you spend on resilience and mitigation before the disaster saves you between $10 and $15 later”, she said.

Called Eco House, Marra and Yeh’s Leura home has won architecture and sustainability awards. A headline on a feature in The New York Times teased readers with a reference to the home’s “secret sauce”, an engineered wax socked away in the home’s insulation that has been tested in space by NASA.

It works like olive oil, said Marra, solidifying in the cold and liquefying in the heat. As it solidifies, it releases that heat back into the home, and vice versa.

An example of the engineered wax used to keep the Eco House cooler in summer and warmer in winter.

Their wax is set to maintain a year-round temperature of 22 to 24 degrees.

“When the sun heats up via big north-facing windows in winter, the spaces warm up and stay warm until about 9pm, after the sun has set behind the hill at 4pm. It provides five hours of essentially free energy,” Marra said. The reverse happens in summer, cooling the house for a similar period of time.

Paired with insulation, double glazing and the positioning of the home, they only need to turn on a heater – powered by their solar panels – for a short period.

“I think [the wax] works brilliantly … it’s just free, free heating,” she said.

The couple bought the site in 2017, and sat on it for years while attempting to understand its ecology.

Like all their projects, the solution began with nature. They removed weeds and the remains of a fruit orchard that had “completely decimated” the native vegetation vital to the health of the hanging swamp that ran through the sandstone layers underneath. These layers naturally filter Sydneysiders’ drinking water.

Working for themselves allowed them to be more experimental, Marra said. Instead of building on the site, they built above it, using screw pile foundations to lift the home off the ground, above the water that pours down the hill in heavy rain.

They also opted for a smaller house – three large flexible rooms that can be configured as bedrooms or living spaces – than most projects. “So many clients think they need a giant house to accommodate their needs,” said Marra.

They located their home at the base of the slope, away from other homes that may spread fires through ember transmission, a major risk. The new native plants – including blue flax lily and common rush – retain moisture, reducing the chance that a fire will spark, and also slow water flows in heavy rains.

Many home buyers avoid steep blocks, but Marra says they provide better views, better sun access and an opportunity to split the levels of the home into different zones that can be independently contained or opened up seasonally.

Alix Pearce, the Insurance Council of Australia’s general manager of climate, social policy and international engagement, agreed every dollar invested in prevention and mitigation saved many times that amount in recovery costs after natural disasters strike.

Pearce said measures to mitigate flood and fires, like elevated floors, flood-resistant materials such as paint, and ember protection, can attract lower insurance premiums where they meaningfully reduce risk. Insurers assess risk at a property level, considering location, construction type and resilience.

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