Sustainability or 'sustainable development' has become a term which is frequently applied to land use and social planning and resource issues. Sustainability is a concept which draws attention to development practices which can degrade natural ecosystems and deplete natural resources. If development is defined broadly to include any cultural activity, then sustainable development may be defined as any practice that meets the needs of the present population without compromising the ability of future generations to meet their own needs (Jacobs 1991). The Rio Declaration on Environment and Development greatly expands on the definition of sustainability (United Nations 1992). It is a set of 27 principles which are strongly tied to concepts of equity - national and international, gender and wealth and inter-generational equity.
Moving towards the goal of a sustainable world is a challenging task. There are many areas of the social and economic arena which need close attention. One concerns existing development and retrofitting it to use less water and energy. The article describes an existing house in Sydney which has been remodeled to bring a significant degree of environmental responsibility. The article also points out that there are disadvantages in this process as well as benefits; that there are financial costs involved, both public and private; and that the financial implications are not completely adverse, especially in the long term.
Concern for natural resources is one of the cornerstones of sustainability philosophy and the first examples of its application in the development process are beginning to be seen. Applying sustainable development principles at this stage is largely restricted to residential development and tends to be site and purpose specific. There are relatively few instances at the subdivision scale. The ten dwelling community of Stringybark Grove in inner Sydney (DEM 1993) is one example. It was built to demonstrate how energy efficiency and water conservation techniques could be provided at reasonable cost in medium density housing. Another is the Sydney Olympics 2000 village project consisting of some 1500 dwellings which will be built using sustainable development principles (Department of Urban Affairs and Planning 1996).
There are many examples of individual dwellings in Australia which fall into the category of being environmentally responsible. There are literally hundreds of examples in the US, Canada, and Europe. All display concern with waste generation and disposal, water use, energy efficiency and use of building material resources to varying degrees. Most of these houses are new and some are expensive because they use high technology solar devices or because extensive research work was needed to produce new building materials from recycled products. A few houses lie at the other end of the price scale, primarily because they have used passive solar design or waste materials. An example is 'Earthship' near Sedona in Arizona which used aluminum cans and discarded car tires as the basis for wall structures. There are many individual buildings on the north coast of New South Wales which apply similar principles.
There are few examples of existing homes which have been retrofitted to bring a greater degree of environmental responsibility. However, in Sydney, Australia, a two story inner city terrace has been surgically modified and the house for all practical purposes has been disconnected from public water and sewerage services. The house sits on a 130 square meter site (including a 48 sq. m garden) only two kilometers from Sydney's central business district. The dwelling boasts a solar energy system, a waste treatment system, a water supply system, and a small wetland.
The Energy System
The PV array frequently generates surplus power which is metered into the main grid and sold to the power company at 10.4 cents/kWh. A second meter had to be installed to register the owners' PV contribution to the main grid. At night and on cloudy days, the PV array does not produce enough power and it is bought from the main grid at exactly the same price. The weather was cloudy on the day of the visit to the house and the PV array was only generating about 450 watts. The main grid thus acts as a storage system without the problem of large numbers of on-site batteries.
The Water System
The potable supply is rainwater which is gathered directly off the roof and stored in a tank partially underground in the back yard. Specially designed rainwater gutters act as the first filter for grit, leaves and other debris. A second potable water filter is activated after rain: the first flush of 8-10 liters of roof water contains particulates and is diverted from the potable supply to the garden.
A pump returns the potable water in the storage tank to the house where it is used for drinking, cooking, showers, and dishwashing. It is not used for toilets or laundry. There is usually a small shortfall of potable water (Table 1) which is supplemented with water from the next door neighbor's municipal supply at this stage. Augmentation from the 'non-potable' or wastewater supply is being studied.
Water quality of the potable supply is tested every two weeks. It is visibly clearer than municipal water and other results indicate that it is lower in metal content and coliform count. Cryptosperidium and benzene have not been tested yet.
The Waste Treatment System Conventional equipment like a flush toilet, clothes, and dish washing machines are used in the house and all blackwater, greywater, and vegetable scraps go into a concrete 'Dowmus' composting tank under the backyard. The Dowmus system works on a simple biological cycle, the secret to which is the worm. Large numbers of composting worms perform a biological ballet to convert quantities of organic household waste into a rich compost. No chemicals are applied and there is no odor noticeable.
Effluent leaving the waste composting system is sterilized using ultra-violet light. There is zero coliform count. The effluent is pumped back to the house for toilet flushing and to the laundry. Overflow from the Dowmus and from the potable supply is pumped to the head of the yard and it trickles as a tiny creek through to a miniature reed bed. This forms the small 3 m2 wetlands in the back garden whose function is to absorb stormwater before it leaves the site. It has also become an urban sanctuary for at least two frog species, other insects, and native birds.). Stormwater also seeps by gravity down the site into the wetlands. Little storm and wastewater actually exits the wetlands or the site unless rainfall is continuous and heavy.
It is thought that the composting system will reach equilibrium in 6-9 months at which point the water is expected to be as clear as the potable rainwater supply from the kitchen tap. Effluent monitoring is now taking place for turbidity and color, for salt and nitrates, and for bacteria, viruses and parasites. It is anticipated that the 'non-potable' supply will be as high in quality as the potable rainwater and that a formal permit will eventually be issued by the local Council.
The Costs of Retrofitting Sustainable Services
Capital costs for the terrace house renovation were A$45,000. Net recurrent savings are $1235 per year yielding a payback period for the investment of 36 years. Assuming a useful life of 20 years for the capital equipment and a discount rate of 7% per year, the net present value (NPR) of the sustainable house is negative, that is, minus $35,107. In terms of technology and installation prices, the exercise is not attractive in a purely economic sense (Abrahams and Walker 1996). One reason is that the owners had already paid for the existing infrastructure when they purchased the dwelling and were effectively paying twice for the same services.
If the investment analysis and the same assumptions were applied to a new house, the NPR of the project becomes positive at +$16,500 (Abrahams and Walker 1996). Such investments are likely to become even more attractive in the future as solar cells become more efficient and cheaper and as the costs of providing conventional services increase.