Case Study - Mystery Bay House
Date:
December, 2024
Written by:
Christiane Partl
Published in:
Pip Magazine, Issue 34
Sustainable Design on the Sapphire Coast
Mystery Bay House is more than just a home, it’s a model for sustainable living. Designed by owner and architect Rob Hawkins and his son Jack, this house operates entirely off-grid, powered by solar energy, featuring thick rammed earth walls, rainwater collection systems, and passive heating and cooling - a blueprint for how to live sustainably without sacrificing comfort or style.
A Thoughtful Response to the Natural Environment
Situated on a 100-acre property between Tilba Lake and Eurobodalla National Park, and the Pacific Ocean to the east, Mystery Bay House integrates seamlessly with its natural surroundings. Named Munggura meaning home-belong in the local Dhurga language, the house pays tribute and respect to the land it was built on. Anchored into the landscape and positioned below the ridgeline to preserve the natural silhouette of the hill, the house follows the landscape’s contours, orienting west toward Gulaga (Mother Mountain), a sacred place for the Yuin people.
The location called for a thoughtful design that worked with the environment rather than against it as the site presented several challenges with strong northeast winds and cold southwest gusts. Rob and his family saw this as opportunities to enhance the home’s performance and comfort; “We spent months camping on the land to understand the climate, winds, and views, ensuring the house would sit perfectly in harmony with the surroundings”.
What is a sustainable house?
As we all know the word sustainable gets thrown around a lot, so what actually makes a home sustainable. There are several aspects to this; the materials used to build it need to be a from a renewable resources with low embodied carbon. Reducing energy consumption and carbon footprint during construction and over the lifespan of the building is crucial, and this includes using energy-efficient household appliances.
Sustainable homes are inherently energy-efficient, which means they cost less to run over time. Incorporating recycled and reclaimed materials during construction also helps lower the environmental impact. While building a sustainable home may involve higher upfront costs, the long-term savings and benefits far outweigh this. They offer a better quality of living as they provide a healthy environment and are designed in a way that directly responds to the site and local climate.
Solar Power: Generating Energy Independence
Mystery Bay House generates all its electricity through a 7.15kW solar power system. In true sustainable fashion, the solar power system was installed on the property’s shed before construction began, ensuring that the entire building process was powered by renewable energy. This not only saved the project from relying on noisy petrol generators but also demonstrated the practical, real-world application of off-grid living from day one.
On a typical day, the system produces between 21.33 kWh in winter and 31.98 kWh in summer, ensuring the house runs smoothly year-round.
The solar energy is stored in two BYD lithium battery banks, allowing the house to function even on cloudy days. A petrol generator is linked to the system as a backup, though it has only been needed once since the family moved in—following ash build-up from nearby bushfires.
The Hawkins family also uses solar power for hot water, with two solar hot water panels linked to three gas boosters. These gas boosters are programmed to switch off once the water reaches the outlet, ensuring that the system operates as efficiently as possible.
For homeowners looking to reduce their reliance on traditional energy sources, solar power offers a practical, environmentally friendly solution. While the initial installation costs may be higher, the long-term savings and environmental benefits make it a worthwhile investment.
Rammed Earth Walls: Passive Heating and Cooling
One of the most striking features of Mystery Bay House is its rammed earth wall. This 60-metre-long wall runs the length of the building, serving as a key element of the home’s passive heating and cooling system. Varying in thickness from 450mm to 900mm, the wall provides natural insulation, helping regulate indoor temperatures year-round.
In summer, the rammed earth absorbs and stores heat during the day, preventing it from entering the living spaces. While in winter, the wall absorbs warmth from the sun and slowly radiates it back into the house as the ambient temperature decreases, reducing the need for artificial heating. “Generally, you can get the house 10 degrees warmer than outside in the winter and 10 degrees cooler in the summer,” Mr Hawkins said.
Rammed earth as a building material that has been used for centuries, created by compacting natural materials such as earth, clay, and aggregate into solid walls. These walls are incredibly durable, requiring little maintenance and providing excellent thermal performance. In Mystery Bay House, the rammed earth wall is not only a functional element but also a design feature that grounds the house in its natural surroundings.
Rainwater Harvesting: A Closed-Loop System
Water is another vital resource that Mystery Bay House manages off-grid. The large roof area collects all the rainwater needed year round for the household, with six 10,000-litre tanks and a 105,000-litre underground tank providing ample storage capacity. The water is filtered through a settlement system and used for drinking, washing, and irrigation.
The house has been designed to handle extended dry periods, with enough water stored to last through six months without rain. Low-flow fixtures and fittings throughout the house help minimise water usage, further extending the system’s efficiency.
Wastewater is managed on-site with a two-stage septic system. Both black and grey water are treated and then pumped to a ‘Wisconsin mound’ absorption system, which was specially designed to suit the site’s clay soil. This ensures that waste is handled sustainably, without any risk of contaminating nearby waterways.
To protect the house from bushfires, a portion of the water tanks is reserved for firefighting purposes, with 48,000 litres on hand at all times. The house is built to Bushfire Attack Level (BAL) 12.5 standards, meaning it is well-equipped to withstand moderate bushfire exposure with a stay-and-defend bushfire plan and evacuation route to the lake as a backup.
Embracing the Natural Environment
Mystery Bay House was designed to embrace the natural elements, from its orientation to its materials. The long, linear layout allows the house to capture cross-ventilation, with strategically placed louvre windows and doors catching cooling breezes from the northeast in summer. In winter, the house’s orientation maximises sunlight, allowing the thermal mass of the rammed earth wall and concrete floors to absorb heat during the day and release it at night.
The homes’s western aspect, chosen for its breathtaking views of Lake Tilba and Gulaga Mountain, posed a design challenge in terms of managing solar gain. To address this, the expansive windows have sliding batten screens to shield the living area from the harsh western sun during summer while still allowing for views. Rotatable batten screens reduce the heat load on the bedroom wing during summer while admitting the winter sun. These operable screens which also serve as adjustable windbreaks, are a key element of the design, ensuring a comfortable indoor climate and allowing the family to open the house completely to the surrounding landscape or close it off for protection. Large blackbutt-framed glazed doors can slide away, creating a seamless transition from indoors with the outdoors. This flexibility allows the house to adapt to changing weather conditions, making it both functional and comfortable in all seasons.
The recycled jarrah exterior cladding pays homage to the numerous coastal banksia on site, and almost hides the home completely from a distance.
Regenerating the Landscape and Giving Back
Beyond the house itself, Rob and his family have made a significant effort to regenerate the surrounding landscape. Over 300 native plants and trees have been planted on the property, including banksias, cycads, and spotted gums. These plants are helping to restore previously cleared grazing land and provide habitat for local wildlife. Replanting the lake’s edge and saltmarshes are also part of a larger effort to restore the environment and support endangered shorebird habitats. The property is home to a thriving ecosystem, with kangaroos, echidnas, and wallabies grazing freely. Rob hopes to dedicate a portion of the land as a wildlife refuge, potentially for koalas, further contributing to the protection of native species. By restoring the natural landscape and supporting biodiversity, the Hawkins family is ensuring that the land can continue to thrive.
Thoughtful Waste Management
Waste was a key consideration during the construction and daily operation of the house. Remarkably, only four trailer loads of landfill waste, mostly plastic packaging, were produced during construction. Any surplus materials were carefully sorted and stockpiled for future projects, minimising environmental impact.
In everyday life, the family takes a similarly mindful approach. All organic and food waste is composted on-site and used to nourish the garden. Household waste is sorted and driven to the local waste management facility in Broulee, with the family generating only four wheelie bins of landfill per year. Non-recyclable packaging and non-compostable food scraps make up the bulk of this waste, while paper, cardboard, bottles, and plastics are recycled, contributing to their low environmental footprint.
A Blueprint for a Sustainable Future
Mystery Bay House stands as a remarkable example to what can be achieved when sustainability is prioritised in design and construction. By embracing off-grid technologies, passive design, and regenerative landscaping, Rob Hawkins and his family have created a home that is both functional and beautiful—a true reflection of their respect for the land. “We never questioned why build a sustainable house, there was just a sense of knowing this is what you do” explains Rob.
For anyone looking to build or renovate with sustainability in mind, Mystery Bay House offers valuable insights. It shows us that eco-friendly living is not just achievable, but also a source of joy, comfort, and connection to the environment. As we look toward the future, homes like Mystery Bay House provide a blueprint for how we can live harmoniously with the natural world.
Date:
December, 2024
Written by:
Christiane Partl
Published in:
Pip Magazine, Issue 34