The couple, who were interested in sustainable construction and design, then began searching for alternative homes that did not need to be connected to the power or water grid.

With a young daughter, Evie and Tristan wanted to build a home that would last a lifetime and provide an example of sustainable living.

"Our child is three, and I think it's really important for her to learn that it's not always about buying something new; instead, by building quality things by hand you can make them last forever," Evie said.

In looking for design ideas, the couple stumbled across Earthships. Popularised by US architect Michael Reynolds, Earthships are passive solar homes built with recycled materials.

Luckily, one of the first Earthships constructed in Australia is in the Adelaide Hills, not too far from Evie and Tristan's property on the Fleurieu Peninsula.

"It's a BnB, so we decided that we would go and stay there for a night," Evie said. "We went there in the middle of winter, and it was 5 degrees outside and 18 or 19 degrees inside the Earthship without the fire on or anything. That immediately made us go, 'Wow, this really works.'"

Earthships must have a particular design and orientation. The front of the home, a glass facade with a plant-filled atrium inside, is directed north, while the home backs onto a large earth mound or berm facing south.

This enables the home to self-regulate its temperature by capturing the maximum sunlight in the winter and convection currents that draw cool air through the berm in summer.

Luckily, said Evie, their chosen site on the property was suitable for this. The next step was to get building.

While the recycled materials are cheap - the home's total cost is about $450,000 - Earthships are labour intensive to build.

Major walls are constructed from old tyres filled with rammed earth, and other walls are built from cob reinforced with recycled glass bottles and cans.

COVID-19 scuppered the possibility for international helpers connected with Reynold's US-based building school, so Evie reached out to locals for help.

"There must've been a lot of people that were just waiting for the opportunity to do something like this because anytime that we've run a workshop or working bee, we had at least 10 to 15 people here to help us out."

This meant the tyre structure was finished in three weeks with 20 to 40 people on site assisting.

This Earthship is one part of Sustainable House Day 2021. The event, which runs online until October 17, highlights those who are putting into practice methods of limiting the environmental impact of households, which generate at least one-fifth of Australia's greenhouse gas emissions.

When Earthship is complete, all power will come from a solar array with battery and water from tanks onsite. Greywater can be used in the planter, subject to approval from SA Health. Similar approvals have been granted for the Earthship in Ironbank. The family will feed themselves from the internal garden and outdoor permaculture paddock plus chickens and some livestock.

While there have been challenges building this unique home, Evie said the end result would serve her family for a lifetime.

"We can feel good about the house that we live in."