The Autonomous House, a model for suburban sustainability  

by Brenda and Robert Vale  

A truly environmentally conscious house would use no fossil fuels and create no environmental pollution.

The Autonomous House represents an attempt to produce such a house near the centre of a small English town, where the shops and services are accessible on foot.





The house is self-sufficient in energy, water supply, sewage treatment and waste water disposal, and is connected to no mains services except the telephone, and electricity, so that it can export surplus solar power to the National Grid.


The total cost of the house, including the photovoltaic generating system, but excluding the land, was £145,000 (approx $NZ 360,000 $Aus 300,000).

This cost was comparable with that of a conventional house of similar size

The floor area of the heated space is 176 m2, but the total
area of the house,  including a full cellar and a double height double glazed conservatory, is 290 m2.


The Autonomous House was the first grid- connected solar house in the U.K.



The site has an annual rainfall of about 570 mm and approximately 3344 degree days to a base temperature of 18oC. (1)



Water demand is reduced by the use of a waterless composting toilet serving the two bathrooms, meaning that the sewage is turned from a "waste" into a useful garden fertiliser.





For the year beginning July 28, 1994 the Autonomous House used a total of 3,115 kWh/year of electricity, of which 1,615 kWh/year, or 52%, was generated from the photovoltaic array.

The carbon dioxide emissions from the Autonomous House relate only to its 
mains electricity use;

It also uses a few hundred kg of wood, but wood is a net zero CO2 fuel) and amount to 5.0 kg/m2 per year, (885 kg for the whole house) compared to a conventional U.K. house which will have a CO2
emission of around 100 kg/m2 per year (8,200 kg) (6).

Even in its uncompleted form, without the heat pump, the autonomous house demonstrates a 95% reduction in domestic CO2 emissions compared to a conventional U.K. house, suggesting a considerable increase in sustainability.


Water consumption is limited to showers rather than baths, and there is only grey water garden watering.

The services in the Autonomous House are provided at no financial cost to the user, but they are, effectively, rationed, because they are limited to what the house can collect from its site, be it water or solar radiation.






The first group of autonomous houses to be built in Britain is under construction about 5 kilometres north of Southwell.






The houses are owned by a cooperative, and rented to the individual members, with a series of constraints written into the leases covering such matters as the number of fossil fuelled vehicles (one car or van only) that may be owned by each household.

The work has taken typical U.K. dwelling types, from a one-bedroom flat to a four bedroom detached house, and looked at the design, construction and specification changes that would be needed to achieve the specified targets.






Possible savings are increased by the fact that roads in such subdivisions could be made without drainage systems, relying instead on porous construction to return surface water to the soil.















If people can be persuaded to adopt sustainability in the home, they are likely to adopt it at work and in other areas of life; the converse is less likely.  It is possible to allocate CO2 emissions to food energy quite simply by assuming that the food production and distribution system uses one third natural gas, one third oil and one third electricity.

• lime whitewash was use internally and German organic paint externally in place of conventional paints;
• the excavations were backfilled with broken brick from demolition sites;
• rather than with newly-dug stone;
• the concrete blocks for the cellar were made of waste ash from the local power station;
• the driveway was made of mining waste;
• the porch was roofed with recycled slates and the bricks for the external walls were fired with landfill gas from decomposing garbage.
• All heavy materials were sourced as close as possible to the site to minimise transport energy demands. 

The Autonomous House is traditional in construction and appearance, but thermally heavy (720 kg of useable mass per m2 of floor area, whereas a conventional U.K. masonry house will have about 200 kg/m2 of available mass) and extremely highly insulated (the roof insulation is 500 mm thick, for example) to retain heat in the building fabric and to make use of incidental heat gains from the sun and the occupants.

A small 4.5 kW woodburning stove is provided in the ground floor hall as a source of auxiliary heating, and to provide a focal point at the entry. Living rooms are placed upstairs to gain better daylight above the dense planting on the site perimeter, with bedrooms and bathrooms on the ground floor.

The house is designed to have a life of at least 500 years so it is detailed to minimise maintenance, with no exposed external woodwork except the window frames.

Site and services.
The total site area is about 600 m2, so the house could be built at a density of over 16 per hectare (nearly seven per acre, a relatively high suburban density).

 The house is in the centre of a town, and all mains services (water, electricity, gas, sewerage and telephone) are available in the street.

 However, the Autonomous House provides its own servicing as much as possible, both to demonstrate a lower-cost alternative to the privatised monopolies that supply these services in England, and to reduce the environmental impact associated with large-scale centralised systems. 

Rainwater is collected from the house roof and that of the conservatory to form the only water supply. This water is stored in 20 recycled Israeli bulk orange juice tanks, each holding 1,500 litres, in two of the four bays of the cellar. It is filtered before being pumped to the house, and wastewater (containing only soap) is allowed to seep back into the soil via an underground soakaway pit.

Electricity is generated by 20 m2 of polycrystalline photovoltaic panels mounted at a slope of 45 degrees and facing due south (because the site is in the northern hemisphere) on a pergola of untreated English oak running across the rear garden.

The 2.2 kW panel array is grid-linked through an inverter, so that surplus solar electricity can be supplied to the local community, and power can be drawn from the grid at night or on overcast days.

Electricity is used for water heating, cooking, lights and appliances and water pumping and sewage treatment.

Resource use
A "typical household" in the U.K. uses 3,000 kWh of electricity per annum for lights and appliances alone, (2), about 36.6 kWh/m2/year just for electricity. The Autonomous House, by comparison, uses only 8.5 kWh/m2/year of non-renewable energy for its total energy needs, or 1,500 kWh of mains electricity.

Over the winter of 1994-1995, from the end of October to the end of February, the house used 315 kg of wood for space heating, which represents about 1,400 kWh of delivered energy, or about 8.0 kWh/m2 of heated area. The temperature in the living room reached a low of 16oC in mid-January, 1995, and then rose to a maximum of 27oC in the very hot August of 1995.

Water consumption was 34 litres per head per day, made up of 21 litres of cold water and 13 litres of hot.

These figures can be compared to an average U.K. house as shown in the table below.

The planned installation of a heat pump for domestic hot water supply, taking heat from the exhaust air of the sewage composter, will reduce the annual CO2 emission and the annual fossil fuel consumption of the Autonomous House to zero.

Compared to international examples, the performance of the autonomous house in use is impressive.  

      However, some of this performance is achieved at the expense of what may be perceived as current living standards.

Living in the Autonomous House.
For example, the Autonomous House has a limited range of electrical appliances - no dishwasher, no freezer - and those that it does have are used in unconventional ways; the washing machine for instance is used only with cold water and no heating, (cold water detergents are not readily available in the U.K.).

Average winter indoor temperatures in the living areas are in the region of 18oC, rather than the 23oC of the Brampton Advanced House in Canada, but the lower air temperature is mitigated by the high radiant temperature resulting from the thermally massive construction.  

The low indoor temperatures are not unique to the Autonomous House, and do not appear to be linked to its deliberately simple technology. The extremely expensive "high-tech" Self- sufficient Solar House built by the Fraunhofer Institute for Solar Energy Systems in Freiburg, Germany, recorded minimum temperatures in the living room of about 15oC in November and January of the 1993-1994 winter. (11).

The occupants of the house commented:  "A significant period for assessing the effect of living without a conventional heating system was provided by the 18 foggy days without any sun, caused by inversion weather conditions on the Rhine plain in February. The room temperature fell noticeably lower than the predicted 18oC limit. It was too cold in the house, but still bearable. Our tea consumption increased - a very efficient form of interior heating - and we went to bed earlier than usual. This made it very clear to us that the house was completely dependent on the sun.

Having to wait for the sun was an unusual but valuable experience in a world in which we are accustomed to getting everything that we want immediately." (12)  

 Whether it is possible to achieve sustainable development while meeting the ever-increasing demands for services that are implicit in the lifestyle of the western world is an open question.

The question becomes even more complex if rising world population and the desire of developing countries to achieve higher material living standards are taken into consideration. It may well be that the Autonomous House points the way forward to sustainability by offering its occupants not "more" comfort and services, but "enough".

A hundred autonomous houses
The local authority, Newark and Sherwood District Council, has now called, as part of its official housing policy, for a hundred autonomous houses to be built in the area by the end of the century.  

The project, which was instigated by Nick Martin, the builder of the Autonomous House at Southwell, and designed by Brenda and Robert Vale, consists of five earth-sheltered single storey houses set into a slight south slope on the edge of the small village of Hockerton.

This project starts to meet the Newark and Sherwood District Council target of 100 such houses by the end of the century.  The houses are designed to need no space heating. Energy, water and sewage treatment will be provided by autonomous zero carbon dioxide systems.
Food will be grown on site using permaculture techniques.

The status of the Hockerton Housing Project as of October 1997 is that it is under construction and will be completed on site early in 1998.  

Research - 3 new UK housing categories.
Following the success of the Autonomous House, and the start of construction of the Hockerton Housing Project, Brenda and Robert Vale are carrying out research on behalf of the Building Research Establishment and Newark and Sherwood District Council into the design of three new categories of housing for the U.K.;

• "Zero heating" (needing no space heating),
• "Zero Carbon Dioxide" (no net CO2 emissions in use) and 
• "Autonomous" (as the others but with its own water and sewage treatment systems).

Initial findings from the research suggest that for a three bedroom semi-detached house (the commonest type in the U.K.) the "Zero Carbon Dioxide" target could be achieved at no extra cost compared to living in a standard house.

This means that all new housing throughout the U.K. could be built with zero emissions. If this is possible in the U.K., with its low levels of solar radiation and its relatively cold winters, it would be much easier in Australia or New Zealand.  

The Autonomous Subdivision.
The implications of low-cost autonomous houses for the costs of infrastructure provision in new subdivisions are interesting. An autonomous subdivision would need only relatively cheap electricity supplies (for two-way exchange of solar electricity with the grid) and telephones, rather than the conventional situation of water, sewerage (and possibly gas) in addition.

The conventional services are expensive to install (historically the costs of stormwater drains, sewers and water supplies have amounted to about 15% of the cost of a house plot over the last nine years in new Auckland subdivisions; by comparison the cost of installing an electricity supply is only about 2% of the cost of a house plot.) (13) These reticulated services have high up- and down-stream costs (charges to the householder, water purification, sewage treatment) in addition to the costs of the pipes.

A recent estimate of these costs states "The average infrastructure cost for every new block in the outer suburbs of Sydney and Melbourne is now estimated at $50,000," (14) This figure probably includes road costs as well as services.

It looks likely that the additional costs per house for autonomous systems could be covered by savings in reticulated services, with the added advantage of no running costs for the householder compared with the conventional situation.  The current cost of the stormwater, water and sewerage services for a single section (or block) in an Auckland subdivision is $NZ7,800. (see reference 13) The additional annual charge is about $NZ50 per month. (15) This would capitalise about $NZ5,000 as a mortgage, so the cost of autonomous water and sewerage could be up to $NZ12,800 without any extra cost to the householder.

There would be the added attractions that the charges would not increase annually, and that the cost of water and sewerage would reduce to zero once the mortgage was paid off.

Since the cost of a composting toilet, a drainage field for grey water and a 25,000 litre rainwater tank in the Auckland area is about $NZ10,000, it would seem that autonomous servicing, at least for water and sewage treatment, is not only better for the environment, but also cheaper than the conventional system.  

Suburban Food Production Reduces Energy Use
Another important aspect of suburban sustainability is that of food production. Using the recommended daily calorie allowances given by the Food and Agriculture Organisation of the United Nations, and assuming no wastage, a household of two adults and two teenagers will eat food with an energy content of 12.8 kWh per day. (16)

However, this is the calorific value of the food as food. To grow the food, transport it to a processor, and then to the consumer also consumes energy. Calculations made using U.K. data from 1968 showed that the energy use attributable to the entire U.K. food supply system was five times the energy content of the food itself. (17) This would increase the energy input to a household due to food consumption to 64 kWh per day, or nearly 24,000 kWh per year.

It has been suggested recently that the current energy multiplier for food in Australia is more likely ten times the energy content of the food, (18) due in part to the increased consumption of processed and "convenience" foods.  

CO2 emissions
One way to rank the environmental impact of different patterns of energy consumption is to compare their carbon dioxide emissions. In the U.K. the domestic sector of the economy is responsible for about a quarter of CO2 emissions, nearly twice those of the "commercial and public services" sector. (19) It consumes 30% of the country's energy, and this is not including its share of food or transport energy. (20) This means that housing is an essential area to tackle if the ecological impact of the built environment is to be reduced.

In Australia and New Zealand the housing sector also uses more energy than the commercial buildings sector, although its overall share of national consumption is lower than in the U.K. In New Zealand the domestic sector takes 13% of the national energy demand compared with 9% for the commercial buildings sector. (21)

In Australia the figures are 12% and 8% respectively (22) but the domestic sector is responsible for 17% of Australia's CO2 emissions, probably because of the use of coal for the generation of electricity, whereas in New Zealand where over three quarters of electricity generation is from renewables, the domestic sector produces only 6% of national CO2 emissions. (23) However, the domestic sector is more important than these simple figures suggest because it is where everybody lives.

It can be assumed that no coal is consumed directly in food production. Current CO2 emissions for the U.K. in kgCO2/kWh are:  natural gas 0.19 petroleum products 0.27 electricity 0.59 (24) average 0.35 kgCO2/kWh  The U.K. household food energy therefore represents over 8 tonnes per year of CO2 emissions. This is the same emission as would be created by driving 36,000 km annually in a Holden Commodore V8.(25) If the suggested current figure given above for Australia is used, the emission rises to 16 tonnes per year.  

How much the car adds to domestic emissions.
The introduction of the car provides another interesting consideration of domestic emissions. In Auckland, a highly dispersed city of single storey houses on quarter acre sections, the average commuting journey is 12.6 km, and transport produces 40% of Auckland's CO2 emissions, with the average household owning 1.47 cars. (26) In a year the household will travel over 9,200 km to work and back.

The range of fuel consumption of available cars on the urban cycle varies between 21 litres/100 km for a Bentley Continental, to 6 litres/100 km for a Daihatsu Mira, so the commuting emission will vary from 1.4 to 5.0 tonnes per year, with the wealthier household producing more carbon dioxide. (27)

An electric commuter car, such as the Finnish City Bee, uses 11 kWh of electricity to travel 100 km, with a range of 80 km. Used for the household's daily commuting trips such cars could provide all commuting, and other local journeys, from the output of a 10m2 grid-connected photovoltaic array. (28) The cost of the array would be about $NZ10,000, and the car would be a further $NZ20,000. (29) This would provide zero-emissions transport, with petrol, or perhaps bio- fuel, cars being rented as necessary for longer journeys.  

The figures above show the possibilities that are offered by autonomous subdivisions. Houses could have zero emissions, provide their own water and treat their own sewage. They could operate zero-emission transport for the majority of trips.

Finally they could use the suburban garden to produce at least a percentage of their food needs. In fact this last point is perhaps the most important.

The best thing anyone can do to reduce carbon dioxide emissions and increase sustainability in their individual life is to grow as much food as possible at home.  


REFERENCES  

1. Page J. and Lebens R. (eds) (1986) Climate in the United Kingdom. HMSO, London. p 245
  
2. Boardman B. et al (1995) "Executive summary" DECADE second year report Energy and Environment Programme, Environmental Change Unit, University of Oxford. p. 2  

3. Figures for space and water heating calculated from data in Bell M., Lowe R. and Roberts P. (1996) Energy efficiency in housing Avebury, Aldershot, UK. pp 23-24  

4. Figure for lights and appliances from reference 2  

5. Water consumption from Twort A., Law F., Crowley F. and Ratnayaka D. (1993) Water Supply (Fourth edition) Table 1.2 p 6  

6. calculated from data in Prior J.J., Raw G.J. and Charlesworth J.L. (1991) BREEAM/New Homes Version 3/91 Building Research Establishment, Garston, Watford, UK. p. 6  

7. Waterloo Green Home, Canada: data for non-renewable energy calculated from data given in Grady W. (1993) Green Home: planning and building the environmentally advanced house Camden House Publishing, Ontario. pp. 93 and 144  

8. Brampton Advanced House, Canada: data for non-renewable energy calculated from data given in Kokko J. and Carpenter S. (1993) "Performance of the Brampton Advanced House" in Applications and Demonstrations: Proceedings, Volume 3 Innovative Housing '93 Conference, Vancouver, Canada, 21-25 June. pp. 71-80  

9. Autonomous Solar House, Freiburg, Germany: data for non-renewable energy use calculated from data given in Carpenter S. (1995)
Learning from experiences with Advanced Houses of the world; CADDET Analyses Series No. 14. Centre for the Analysis and Dissemination of Demonstrated Energy Technologies, Sittard, Netherlands. p 201, based on the fact that the house needed 500 kWh of electricity from a portable generator Fuel consumption calculated from data for Honda 2.2 kW 4-stroke petrol generator supplied by Bowden Marine and Industrial Ltd., Avondale, Auckland, New Zealand, (3.7 litre fuel tank giving 2.8 hours of operation at full power).. Fuel consumption for this generator is typical of a range of small petrol driven generators.  

10 Wädenswil Houses, Switzerland: data for non-renewable energy calculated from data given in Hickling Corporation (1993) "Zero heating energy buildings, Wädenswil, Switzerland" p 5, in Hickling Corporation (1993) Comparison Analysis Report on Advanced Houses (Draft) prepared for EMR/Canmet, Hickling Corporation, Ottawa, Canada  

11. Voss K., Dohlen K.v., Lehmberg H., Stahl W., Wittwer C., Goetzberger A. (1994) "The self-sufficient solar house Freiburg: experience along the way to energy independence" European Conference on energy performance and indoor climate in buildings 24-26 November, Lyon, France. unpaginated  

12. Stahl W. and Stahl H. F. (1993) "Living in the Freiburg self-sufficient solar house" SunWorld Vol. 17 No. 4. December. pp 18-19  

13. data from Maplesden J. (1997) private communication. Harrison Grierson Consultants Ltd., Manurewa, Auckland  

14. Newman P. and Kenworthy J. (1992) Winning back the cities Australian Consumers' Association, Pluto Press Australia. p 4  

15. data from Metro Water, Auckland, 18 October, 1997  

16. calculated from data in Fisher P. and Bender A. (1970) The value of food Oxford University Press. p 22  

17. Leach G. (1975) Energy and food production International Institute for Environment and Development, London. p 8  

18. Treloar G. (1997) private communication. Deakin University, Geelong  

19. Department of the Environment (1992) The UK environment HMSO, London. p 30  

20. DoE op cit. p 214  21. CAE (1994) "Energy efficiency project workshop" Task Group Discussion Papers, Vol 1, Residential buildings/ Commercial and institutional buildings/Transport.

21. Centre for Advanced Engineering, University of Canterbury, New Zealand. February. p 3  

22. Department of Primary Industries and Energy (1995) National sustainable energy policy: a discussion paper. Australian Government Publishing Service, Canberra. p 38  

23. Australian data from Department of Primary Industries and Energy (1995) op cit. p 24. New Zealand data from EECA (1996) Monitoring Quarterly Issue 5 September 1996, Energy Efficiency and Conservation Authority, Wellington  

24. Figures supplied by Evans P. (1997) personal communication Building Research Establishment, Garston, Watford, UK. 11 Feb. The figure for electricity has reduced from a value of 0.832 in 1990 as a result of the increasing use of natural gas rather than coal for generation.  

25. calculated form data in reference 24 and DPIE (1994) Fuel consumption guide Department of Primary Industries and Energy, Canberra. p 14  

26. ARC (1996) Transport facts and figures data sheet Auckland Regional Council Environment, Auckland.  

27. calculated from data in references 24 and 25  

28. data on car from PIVCO, Finland; data on solar array assumes an output of 1200 kwh per annum from a 1 kW array in Australia or New Zealand conditions.
The 7.2 kW array at SEDA in Sydney is quoted as producing an annual output of 1527 kWh/kW in Clement J. (1997)   "The sustainable office" ReNew October-December 1997. p 25  

29. current solar array price from Solar Power Waiheke, Waiheke Island, Auckland; car price for purpose-built glassfibre 2+2 seater from Heron Motor Co., Rotorua, if ordered in lots of 100 at a time.