Building Design

Design strategy

Disturbance to the site is kept to a minimum.

The building uses passive systems to maintain comfort:
• Passive Heating
• Passive Cooling
• Natural Ventilation

Renewable energy sources are used wherever possible:
• Solar hot water system
• Photovoltaic panels for power generation
• Good daylighting

High efficiency energy converters, or gas is used throughout
• High efficiency lights at night
• High efficiency appliances
• Gas cooking

Materials having low embodied energy are used:
• Use recycled materials
• Earth is used for block walls

Water collection takes place on site. Waste recycling takes place on site where possible.
• Grey water recycling
• Composting of organic waste
• Composting of human wastes

Site development

During the preparation of the site great care was taken to avoid drastic reshaping of the land form. Trees were selectively cleared, keeping a mixture of mature trees while maintaining solar access to the building. Scarring was kept to a minimum when providing vehicle access and parking to the front door.

Since purchasing the Eumundi property in 1993, the Harpers have planted nearly 2000 trees in an effort to re-establish forest cover and in doing so, provide habitat, reduce erosion, provide privacy and absorb greenhouse gases.

Orientation of the house

The house faces north to minimise sun exposure onto and into the house from the east and west. The northerly aspect allows maximum control of the winter and summer sun.

Zoning within the house

The living areas, such as the kitchen and lounge room, are located towards the north-east of the house to get solar access at the right time of day for those parts of the house used the most.

Insulation

Wool insulation in the walls and roof help slow heat gain in summer and heat loss in winter. The roof/ceiling space has R2.5 insulation while the cavity walls have R1.0.

Thermal mass

Thermal mass is used to stabilise diurnal temperature variations, and to store heat due to solar gain. Concrete slab, tiled floors and compressed earth block walls are used throughout the house.

Solar control

The roof overhangs on the northern side of the house keep the summer sun out but allow the winter sun in. Wide eaves also help protect the house by keeping the rain off the windows and balcony.

A solar pergola has been incorporated over the kitchen window to allow the sun to radiate onto the tiled concrete floor in winter. In summer, when the sun is higher in the sky, the pergola shades the window.

Timber louvre windows on the East and West exclude low level light in summer from entering the building in the early morning and late afternoon.

Light colors are used for the roof and external walls to reduce the amount of solar radiation being absorbed, and reducing the resultant heat.

Daylight

The building contains louvred clerestory windows above a wall on the North side of a central passage way. These windows allow sun to shine through the building in winter and exclude it in summer. This provides natural light and thus less dependency on electricity.

These louvres also have a thermal functon. In winter, sections of internal rammed earth wall are heated by the slow passage of sunlight passing over the surface. This heat is later released as the surrounding air cools.

Ventilation

The interior ceilings are angled to naturally allow hot air to rise and then escape through the clerestory louvred windows. Timber louvres allow air flow through the building. The upward angle of the over-hanging roof catches the breezes to help keep the house cool in summer.

Floor vents behind the fridge and inside the earth walled pantry allow cool air to come up from the 'cellar', making the fridge more efficient and keeping food stored in the pantry fresher for longer. The water garden at the front entry helps cool warm northerly breezes before they come in to the house.

Embodied energy

Embodied energy is kept to a minimum through the use of recycled materials and using material available on the site.

• More than half the timber used to build this house is recycled
• Main roof members were old bridge timbers
• Floor boards were cut from purlins and girts pre-dried while in a factory structure.
• Telegraph poles were used as veranda posts.
• Recycled materials also add character
• Walls were made using cement stabilised compacted earth bricks.
• Wherever possible, Australian-made products have been used to support local business and employment and to reduce greenhouse gas emissions from excessive transport of imported goods.

Renewable energy sources

Renewable energy sources are used to provide hot water and for electrical power generation. The solar panels and the solar hot water system are on the roof over the back veranda. They are placed on a north-facing slope to get maximum use of the sun's energy throughout the seasons. All the electrically operated energy efficient apliances, (including a top loading washing machine that has all the water saving capacity of a front loader), run on electricity provided by these solar panels.

The 1.44kW photovoltaic system provides more than enough energy to power the house except on the rare occasions when there are long periods of cloudy weather.

The gas-boosted solar hot water is the most energy efficient and environmentally sound way of heating water. The provision of hot water is commonly the biggest user of electricity in the home. Gas is also used for cooking.

Electrical backup and surplus

When there is insufficient power available from the PV panels, electricity is purchased from sustainable sources - solar, wind, hydro and biogas (methane) - through the Earth's Choice program. Any unused electricity produced by the House is sold to Energex.

Water collection and conservation

Rainwater is collected from the roof into a tank for use in both the home and garden, giving independence from the main reticulation, and decreasing environmental impacts associated with treatment and reticulation of freshwater.

The AAA-rated shower rose uses water efficiently. Front-loading washing machines use less water and less suds, but we don't seem to like them because you can't just throw something in once the washing has started. The special front-loading washing machine that was installed overcomes this problem.

Appliances

Light fittings and electrical appliances have been chosen for their energy efficiency. Major appliances such as refrigerator, washing machine, etc. have been selected based on their high energy star ratings.

The cook top and stove are powered by gas with only minimal use of electricity. This reduces greenhouse gas emissions.

Covered air drying space for clothes has been purpose built to reduce the need for a clothes drier which uses a substantial amount of electricity.

Selection of building materials

Low-toxic finishes have been used wherever possible. For example, natural beeswax-based polish has been used for the timber and tiled floors as well as the furniture. This is in response to concerns about potential health risks associated with modern floor and furniture finishes.

Natural, durable, recycled and renewable building materials have been used throughout. This decreases the amount of waste generated, reduces energy consumption from manufacture and from waste disposal, and lessens the direct impact on the environment from harvesting natural resources.

Composting toilet

A composting toilet allows waste to be filtered into nutrient rich compost that is then used to feed fruit, nut and rainforest trees on the lower half of the property. It requires no water and so reduces black water disposal problems.

Waste disposal

The amount of waste produced is recycled by avoiding packaging where possible, and if not avoid packaging that cannot be recycled or burnt.

Waste separation bins in the kitchen encourage active recycling and appropriate disposal of waste at the point of generation.

Edible landscape that provides an animal habitat

All organic wastes (resources) are recycled on site. The composting toilet and other garden composting bins take organic materials such as vegetable scraps and turn them into the nutrient-rich compost and compost filtrate for the trees and garden. On-site reuse and recycling of 'wastes' reduces the amount of waste going to landfill sites and provides a cost-effective means of safely fertilising the gardens.

Throughout the garden, but particularly in a food production area, there are fruits, nuts and vegetables, including Australian bush tucker, to provide the owners with some of their food requirements. In the long run, this will save time and money. It will also decrese the need to go shopping, and so reduce emissions from car use.

The dam and other water features provide wildlife habitat, as does the regenerating rainforest. Many native forest trees have been planted:

• to prevent erosion, and stabilise the site,
• screen the house from unwanted western sun,
• provide privacy,
• act as a wind break,
• provide habitat for native wildlife,
• and because it's nice to have so many trees around home.