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Assessor's Report

Zero CO2 Housing Competition

A brecsu/riba competition to encourage sustainability in designs for a riverside housing development produced a variety of innovative solutions, including a tree-house development and a coppicing scheme for a self-sufficient fuel source.

Thirty years ago, Robert and Brenda Vale were living on a small- holding in the fens near Ely while working on the Autonomous House project based at Cambridge University School of Architecture. Self-sufficiency was more of a buzz word than sustainability, but the impending energy crisis ensured that their proposals for energy conservation and the use of renewable energy sources became well-known.

Thirty years on, the deep-green agenda has a new sense of urgency. Although the limits to fossil-fuel resources may be less restrictive than were originally envisaged, the tolerance of eco-systems to deal with the pollution resulting from prolific energy usage are much more serious. The acceptance of global warming resulting principally from carbon-dioxide emissions has led to a new interest in the Vales' 30-year-old ecological message.

Last year, the Building Research Establishment published its General Information Report No 53, Building a sustainable future - Homes for an autonomous community. The report represented the culmination of two research projects by the Vales and incorporated a design guide for sustainable housing and specifications for zero CO2, zero heating and autonomous standards for dwellings. To publicise this guide brecsu, in conjunction with the riba, set up an ideas competition to look at the development of housing, in accordance with this brief, on a riverside site in Newark, Nottinghamshire. Competitors were asked to reconsider strategic issues such as car parking, layout and density as well as house design solutions falling within the strict energy and environmental targets set out in gir 53.

The 45 entries received were reviewed by a team of assessors comprising Peter Clegg and Richard Parnaby (riba assessors), Paul Evans and Martin Cook of brecsu, David Pickles of Newark & Shearwood Energy Agency, Nicholas Falk of urbed and David Gale of Gale & Snowden Architects. Peter Rickaby of Rickaby Thompson Associates and Nick Baker of the Martin Centre in Cambridge were asked specifically to comment on the competitors' response to energy issues in the brief.

The assessors were impressed by the variety of architectural and urban solutions proposed, and the fact that, by and large, those schemes which had a strong and successful architectural identity also appeared to meet the energy criteria for the competition. Eight schemes were chosen to go through to the second round of assessment and, in the intervening period, Peter Rickaby undertook a more comprehensive energy analysis of all shortlisted schemes. The reported energy-efficiency strategies were reviewed for viability and credibility. Stated construction U-values were considered (but only recalculated if they were not credible) and competitors' performance assessments were reviewed. All of the shortlisted designs appeared to be capable of achieving at least the 'zero CO2' target of less than 100 kw hrs/m2/yr. Most of them achieved figures of around 80 kw hrs/m2/yr and one appeared to achieve the 'zero heating' energy target of 50 kw hrs/m2/yr.

The second-stage assessment was undertaken by Peter Clegg, Richard Parnaby, Peter Rickaby, Martin Cook and Paul Evans, together with three new assessors, Max Fordham of Max Fordham & Associates, Paul Finch of The Architects' Journal, and Keith Ross, head of housing research at the Building Research Establishment. The jurors found it relatively straightforward to reach a consensus on the placing of the winning entries.

While most of the shortlisted entries achieved densities of around 200 habitable rooms per hectare, the architectural solutions varied considerably. The winning scheme was the only one of the entire 45 entries to dare to build high, in this case only up to six storeys - something that might have been explored in more detail, since the north-west facing riverside site means that overshadowing from tall riverside structures was minimised. Many entrants chose to build along the length of the river with the linear terraces varying from two to four storeys, but few seemed to explore satisfactorily the relationship of the riverside walk, and the possibilities of breaking the terrace form to link the inner site visually to the river.

The alternative format of building terraces almost perpendicular to the river led to some interesting courtyard-type schemes, but provided a more difficult planning challenge in achieving vehicular access.

The most common technical solution to the energy requirements was to combine superinsulation and air-tightness with passive solar design and mechanical ventilation with heat recovery (mvhr). The remaining energy requirement was then satisfied from renewable sources as far as possible. This was a sound strategy, well-rehearsed in gir 53. Very few of the submissions included a credible natural ventilation strategy, and many of them resorted to the 'black box' solution of an mvhr system without really addressing the issues of how such a system might be integrated into the building. Most of the schemes exhibited an engagement with the problems of reducing fabric heat losses, but failed to acknowledge that the consequently increased importance of ventilation loss requires a similar effort to be focused on air-tightness.

The shortlisted submissions contained many interesting and innovative ideas for heating dwellings using renewable energy, but only the winning scheme convincingly addressed the problem of matching demand to the likely renewable supply. Most entrants addressed the issue of space heating, but few seemed to appreciate that, in a well insulated house, hot-water usage can be the largest thermal load. Many of the designs relied on solar collectors or photovoltaics, but the wide range of panel areas suggested a lack of awareness of the amount of useful energy this technology could provide. Few schemes had sensibly located photovoltaic arrays and there seemed to be a lack of appreciation that the use of electricity for lights and appliances in housing is generally the largest source of carbon-dioxide emissions. Although the brief, appropriately, laid emphasis on the significance of energy use in housing, other issues such as water use, the recycling of waste products and consideration of transportation energy and food production figured highly in many schemes.

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