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Model housing

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Technical & practice: A small Nottinghamshire housing development is pioneering ideas about communal sustainability

The Hockerton Housing Project is one of the few built examples in the uk which addresses sustainable housing, as distinct from the creation of separate sustainable houses. Though only a terrace of five units, this development has a wider relevance for Britain. Not only are the houses designed not to require fossil fuel-generated heating, they are also totally self-sufficient in water consumption. And through means such as permaculture the design significantly reduces dependence upon supermarkets for food production.

The architects were Robert and Brenda Vale, working with developer Nick Martin who also constructed their Autonomous House in nearby Southwell. In the technology of ecological design the Hockerton project is altogether more ambitious, and aesthetically it is also little more adventurous. Located to the south of the village of Hockerton near Newark, the project is sufficiently far from the village centre to avoid pressure to conform in terms of urban character, yet not far enough into to the countryside to require total visual camouflage.

The 10ha site chosen by Nick Martin is close to the ideal of a fertile village fringe. Sitting in a lush valley and screened by thick hedges, its modest scale belies its grand sustainability ambitions. The aim was to produce a prototype of ecological self-sufficiency using earth-sheltered principles linked to passive solar gain, on-site water collection and treatment, and extensive waste recycling.

The target was to construct housing within normal housing cost yardsticks: it should generate no atmospheric CO2 emissions from space heating (monitored by bre); it should be pollution-free in operation; and it should harvest and recycle its own water (monitored by bsria) and produce a balanced and socially co-operative community.

Owners of the houses make a commitment (as they do at Findhorn) to help meet the objectives of the estate. Each adult commits themselves to providing eight hours per week to support activities - half for food production, site maintenance and ecological repair, half for various forms of commercial promotion of the project and its ideas.

The construction agenda

Houses have no central heating. Solar and casual gains generate sufficient space heating throughout the year to avoid the need for fuel-consuming heat sources. Double-height conservatories facing south-west transfer enough solar energy to the building fabric to maintain a stable temperature of 19-21degreesC. The high-density construction uses masonry cross-walls, solid floors and earth-sheltering to the north. Between the concrete structure and the earth there is 300mm of cfc-free expanded polystyrene insulation.

The thick cross-walls and solid floors absorb and re-emit energy to create temperature stability (the crosswalls also acting as effective acoustic barriers between dwellings). Summer temperature peaks are reduced by exhausting air through high-level Velux windows in the shaded conservatory roofs and by solar-assisted through-ventilation. In these regards, terraced- house forms are essential for low-energy design.

Houses are wide-fronted with shallow-plans. This allows for maximum passive solar gain with good light penetration to the rear of the building (helped by high ceilings) and also the maximum of earth-sheltering for northern protection.

This does raise questions of cost and buildability. To address buildability, the design standardised the construction using 3m-wide bays and prefabricated concrete floor units. The linear configuration of the development allowed simple, progressive construction with lifting vehicles operating from the concrete base. Simplicity in construction helped keep costs down.

Construction began in August 1996. The first family moved in in February 1998 and the rest of the families over the year as construction progressed - acceptable speed for what was largely a self-build project.

Each house is designed to exploit the potential of natural, traditional materials. The use of standard off-the-shelf products encouraged the development of modular construction, with some economy of scale for purchasing the repetitive high-performance triple-glazed windows and doors (U=1.2W/m2k) Conservatories are double-glazed. All windows use low-emissivity glass.

Materials of construction were selected against the following criteria:

structural integrity and high thermal performance

minimal embodied energy in manufacture, balanced by long-term energy performance

minimal environmental and health hazards, that is non-toxic products and materials

minimal impact on land and resources

environmental policies of manufacturers

readily-available, low-to-medium technology materials

local supply where possible, to minimise transport energy.

Systems performance

With a zero CO2 target, the management of naturally-generated heat became important at every level of design - orientation, construction, servicing and operation. The early decision to use heat-recovery technology allowed the integration of heat pumps, pipe runs and exchanger units within the strategy for construction. The houses use Baxi air management systems to recover heat from stale air which is mechanically-extracted from wet areas - toilets, bathrooms, kitchens - while introducing equivalent volumes of pre-heated, filtered air to the main area of each house. The air-to- air system recovers up to 70 per cent of heat from exhaust air, operating continuously at low speed. The unit has three speeds, however, with a maximum capacity of 400m3/h per house.

A 0.7kW air-to-water heat pump provides domestic hot water via a heat exchanger, using excess heat from the conservatories. Since each house has a 1500 litre hot water tank there is the ability to store gains for up to a week between top-ups.

An aerogenerator was always part of the scheme design. So far there have been three planning rejections but approval is now hoped for following a change in politicans in the recent local elections. The aerogenerator will be connected to the grid, the ambition being zero net annual use of grid electricity rather than electricity-autonomy.

Water conservation has not been ignored. The roofs of the five houses catch an annual 150,000 litres of water, fed via copper gutters into underground tanks. Water is passed through filters followed by ultra-violet treatment for potable water supply. It is estimated that with 20 people in the development this collected volume of water could exceed demand threefold. Storage capacity is 25,000 litres, enough for around 250 days.

Non-potable water is collected from the back of the houses, the road and surrounding fields, channelled to a sump and thence pumped to a 150m3 reservoir, providing around 100 days capacity. From there it is sand-filtered and piped to the houses for all bathing, washing of clothes and flushing of toilets.

Water demand is limited by using low-flush toilets, showers instead of baths, flow restrictors in showerheads and detergent-free clothes-washing to reduce rinsing. Grey water is fed to the nearby lake via septic tanks and reedbeds. Although only just over a year old, the lake already supports six species of breeding waterfowl and fish have been introduced for eating next year.

Hockerton is no normal community. These families are living out an ecological ideal. The planning authority, concerned that the name of sustainability was being exploited to achieve development consent, attached conditions to ensure that project-related work as well houses would be created.

The Hockerton project is one prototype for new build in the twenty-first century. This is not high-tech building but modest, realistic terraced housing. The development represents an important transition from the autonomous house to autonomous housing. The ideas are being further developed by Robert Vale using the semi-detached house as a model, since this appears to offer greater replicability than terraces in Britain.

Brian Edwards is a professor at Huddersfield school of architecture.

Site visits and information from Nick White, tel 01636 816902, email hhp@hockerton.demon.co.uk

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