by a number of small-scale one-off projects. These include a range of individual house types built at Energy World, Milton Keynes (1988);1 Brenda and Robert Vale’s Autonomous House (1994);2the Oxford Solar House by Susan Roaf (1995);3and the Integer House pioneered by the
C ONSTRUCTION
T HE G REEN A GENDA
5
SUMMARY
Given the threat to the global environment, there are four main issues that the large quantity of housing to be constructed in the near future will need to address. The first is conserving energy – ensuring that housing consumes less energy in its day-to-day use. Urban housing has inherent advantages in con- servation but there are key innovations to be made. These include the achievement of higher levels of insulation, garnering the benefits of solar gain and improving the efficiency of ventilation. The second issue is to develop the generation of energy from renewable sources. This is partly a matter for pub- lic policy but new means of gathering and generating energy can be built into houses or groups of homes. The third issue is water management. This is likely to become an increasingly serious concern and should mean changes in the way homes are used. Less water needs to be used and more collected and recycled. A fourth, overarching issue is the conservation of scarce resources and the protection of the wider environment. This has critical implications for the selection of suitable materials for house construction. At the same time, good design should ensure the promotion of a healthy and diverse environ- ment. Alongside these concerns there is a renewed emphasis on ‘off-site con- struction’. System building has a chequered history but new approaches may have benefits in reducing waste, improving quality and speeding the produc- tion of the many new homes needed.
Building Research Establishment (BRE) and realised in two demonstra- tion houses built in Wiltshire (1999).4Abroad, small settlements have been developed as low-energy prototypes such as ‘Sun village’ near Lund in Sweden5or the Solar Village at Amersfoort in Holland.6Similar settle- ments have been proposed for Britain and such communities seem to hark back to a long-held idyll of rural self-sufficiency. What these pro- jects have in common is that they are low destiny and sited in relatively remote locations. The innovations they embody are not necessarily applic- able to urban housing design.
The first major difference is transport. Research has shown that a family living in a very energy-efficient house in a remote location will use more energy overall than a similar family living in a wholly un-insulated traditional house in the inner city simply because of their dependence on the private car.7High-density urban housing makes a substantial contribution to redu- cing carbon emissions simply by engendering more efficient transport. The second major difference is inherent in the form of urban housing. It has been estimated that a two-storey house in the middle of a terrace uses 30 per cent less energy that the equivalent semi-detached house simply because of its smaller proportion of external walls. A flat will show a more or less similar reduction depending on its position in the block.8Urban housing, then, has inherent energy advantages over the low-density forms prevalent in the recent past. There are lessons, though, from the green agenda which can be appropriately applied to make these advantages even greater. Energy consumed in the use of housing can be reduced by mak- ing best use of orientation and by improving insulation and ventilation.
Passive solar gain
The orientation and design of buildings can result in considerable heat gain from sunlight. Some energy may be absorbed in the building fabric but the main gains are through glazed areas. Solar radiation is of short wavelength and can pass through glass – energy reflected off internal surfaces is of longer wavelength and cannot. Radiation cannot escape and heat thus becomes trapped in glazed spaces. Any large glazed area can trap solar energy within buildings.9However, conservatories are sig- nificant design elements which can be used to maximise the collection of solar gain. ‘Sun spaces’ – smaller glazed enclosures attached to the south faces of houses – can have a similar effect. This can include enclosed bal- conies placed at higher levels of buildings. Once gained, it is important that buildings have sufficient thermal mass to absorb the heat and allow it to be released slowly. This usually means high-density materials such as masonry, concrete or dense blockwork.
To the proponents of maximising solar gain, orientation is of critical significance. As Brian Edwards put it in his book on sustainable housing:
Since passive solar gain can make an important contribution to reducing energy consumption in housing (by as much as 18 per cent without house type change) orientation of dwellings should be up to 30° either side of south. Coupled with this, the area of glazing should be restricted on the north and enlarged on the south. As glazing areas are partly a function of room needs this results in houses of different layout according to the aspect… To achieve solar penetration between houses an unobstructed angle of 10° is needed on south elevations.10
The ideal, then, would be housing built in parallel rows all facing south and widely spaced enough to allow maximum penetration of sunlight in winter, though this would vary with latitude.
It would be difficult to form well-functioning streets on this basis since they would be fronted by living rooms and bedrooms on one side and by utility rooms on the other. South elevations can also experience very high heat gains in summer that necessitate shading and heat extraction measures. In hot climates it is customary to protect south façades from the sun. In the design of urban housing there are multiple constraints to address, and a range of priorities of which maximising passive solar gain is but one. The need to define coherent urban blocks, and to create well-defined spaces and streets which are safe, is probably of greater importance. This may mean compromises on solar gain. It is certainly important to avoid placing large glazed areas or main living rooms on north elevations but placing them on the east or west side is acceptable.
This should provide some solar gain while avoiding the high levels of exposure in summer.
Higher insulation levels
To conserve energy in the use of housing it is important to ensure that as much as possible of the heat produced within the home is retained.
Insulation acts as a barrier between the inside and the outside reducing the rate at which heat is lost. The means and methods of insulation have long been well understood. What has changes is the intensity. There has been a focus on raising the standards of insulation both through regula- tion and through the incentive of grants programmes. There have been successful experiments in creating ‘super-insulated’ houses. In these, insulation levels are very high – reducing heat loss so much that conven- tional heating systems can be dispensed with altogether. Sufficient heat is generated by the use of appliances and by human activity to make