Brown Hill Creek project is a newly built underground house that uses earth as defence against potential bushfire attack. This earth sheltered, 7.5 Nathers star, BAL-40 home makes a strong case for comfort, sustainability and bushfire resilience in a long-life, low-maintenance home.

‘Earth-sheltered’ underground housing is not a new concept as people have lived in earth shelters throughout history. Dale says the original interest in building underground was the thermal comfort benefits rather than fire resilience. An earth sheltered house will maintain a natural temperature range of around 15 to 25 degrees, usually sitting around 22 degrees in a temperate climate summer.

More recently clients have been coming to Dale at ShelterSpace with bushfire resilience front of mind, just as Stefan and Emrys did for the Brown Hill Creek Project, which was completed in January 2023 in the hilly, south-east suburbs of Adelaide.

“A properly designed Earth Sheltered House is the most bushfire resistant house available today, because the walls are protected by earth mounds and the roof with half a metre of sand and soil. Because they don’t have a conventional roof space, they eliminate any possibility of embers, sparks or flame entering the interior through the roof, which is the main source of ember ingress in traditional houses” Dale said.

Stefan and Emrys inherited the Brown Hill Creek site from parents but were worried about the bush fire risk. They came to ShelterSpace with a challenging project that had a long, steep and narrow driveway. The access road at the bottom of the driveway was also not easy to get around. “It was difficult to get trucks up there for building, let alone fire defence”, said Dale. So even with improvements to the driveway, they couldn’t rely heavily on Country Fire Services arriving to defend the site.

There were also issues with the waste management location and land use overlays that Dale had to work through with authorities. After many consultations and design discussions, they came up with a project solution that satisfied all concerned.

“Out of all our projects, road issues and septic systems are always the hardest part” says Dale. “Projects like this require patience and understanding from both clients and designers, but the end result and the view from the house [was] worth the wait.”

The house is low to the ground and cut into a north-eastern slope for a favourable solar orientation, which means there is only one elevation that requires any bushfire defence.

When asked what was the most cost-effective, bushfire resilient feature of this project, Dale said the earth-covering. “It’s already onsite, you’re just paying to dig it out and put it back over the building.”

The earth from the cut is reused as fill behind and over a heavy-duty frame of concrete, reinforced blockwork and steel that can hold up the significant weight of wet earth across the concrete roof. There’s a lot of embodied energy in such a structure, so it needs to be a long-life building. But the very low operational energy in maintaining human comfort, will offset the high embodied energy over the building’s lifetime. The sustainability dictum being ‘long-life loose-fit’ construction.

Solving the water diversion and building water-proofing issues is also vital. Brown Hill Creek’s stormwater is initially diverted around the building by swales, followed by waterproofing membranes that direct drainage off the roof and behind the solid walls. Dale recognised how effective this needs to be, as otherwise the smallest leak, not easily located, can lead to a lifetime of dampness, mould and material failure. Hence ‘back-up’ multiple waterproofing systems are usually advisable.

The large concrete water tanks on either side of the underground building have two functions, Dale explained. They provide water, but they have also been used to retain the soil due to their size and weight, which relieves the pressure on the concrete block retaining walls, making for a cheaper solution overall. Dale says, “there is a lot of engineering that goes into retaining walls, and these are an easy solution.” Water collection off earth roofs is both limited and nutrient laden, so they use a nearby metal garage and shed for collection, to store 200,000 litres of water.

Stefan and Emrys were keen to have some rammed earth walls incorporated into the design, so Dale introduced a few non-load-bearing walls at the entry and lounge areas.