Troy Ryan lives on a 4ha bushland property in the Adelaide Hills with his partner, Keirstie, and their two-year-old son, Felix. While previously living and working in the opal mining township of Coober Pedy, Troy fell in love with the dugout style of home, so it was no surprise that, when he was planning to build his own house, he opted for an energy-efficient home under the earth.

“I loved the fact that when it was 45ºC outside, it was only  21ºC inside the buildings,” he says. “I helped a mate build a dugout and he followed one rule – no measuring tapes were allowed. We’ve also followed that rule.” But Troy admits the building’s organic nature and lack of fixed dimensions made it difficult to obtain building permits from the council.

Constructing the home

The first step towards building his underground dwelling, which was eight years in the making, was digging a quarry to remove about 3500 tonnes of earth.

“We then constructed the home from concrete,” says Troy. “It is essentially three main domes, connected by tunnels. And our son’s room is a perfect 5m diameter hemisphere, which is designed to be fun. The other rooms include our bedroom, laundry/bathroom, and the kitchen/dining area.”

Once the concrete was finished the next important step was waterproofing. This involved adding a series of layers to the roof, starting with bitumen and plastic. This was followed by a drainage layer to create an air gap and allow water to drain, then a geo-textile layer to stop mud and dirt getting through. Finally, the soil was added – all 2500 tonnes of it! “This gives us a roof garden about 1.2m deep, which is perfect for the indigenous wallaby grass and grevilleas that thrive in the habitat,” says Troy. “The mulch and moisture of the roof garden also keep the house cool during the year. The grass dies down in summer, because we don’t irrigate it.”

The family is also very conscious of how they use water. “We have about 100,000L of rainwater stored in six tanks and a dam, but that supplies all our household needs and waters the vegies,” says Troy. “So we really need to watch what we use.”

Renewable energy choices

As Troy is a specialist in solar energy, the choice to install renewable energy was easy. The cost of grid connection was about $80,000, but installing solar panels and a wind turbine was cheaper at about $60,000. And there’s the added benefit of helping the environment and a lifetime of no power bills. A 12m wind turbine is positioned on a hill not far from the house and, on a good day, it generates 2–3kWh (kilowatt hours) of energy. This is used in conjunction with 16 solar panels on the nearby workshop building, which generate 6–8kWh daily. Troy estimates the family uses about 3.5–4kWh of energy each day, compared with the average daily household use of 18kWh. “Batteries can store up to 25kWh of energy, which is enough for seven days,” he says. “We do run out of power because of carelessness, but that’s when the diesel generator kicks in. June is the worst month for being short of power because that’s when it’s the least sunny and there is not much wind. In winter a wood heater warms the home and heats water for the shower. The temperature usually stays at an even 17–18ºC.”

Passive solar design makes maximum use of the sun, with north-facing windows warming the living area and providing wonderful views overlooking the valley. “We have single-glazed windows, but these are made from special glass designed to allow radiant heat in from the sun,” says Troy. For Troy, designing and building his underground home has been about being energy efficient and looking after the environment. “We all have to do what we can, irrespective of what we think is going to happen in the future,” he says.

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