Designing public spaces from sustainable resources

Planners and designers can help to minimise carbon emissions through their choice of materials and the resources they incorporate into the design of public space.

Recycled glass in the surface of the Blue Carpet square in Newcastle

Public spaces need to be constructed from sustainable materials if they are to contribute to the lowering of a city’s carbon footprint in the way that is already a core consideration for building design. Databases are being developed for material carbon and embodied energy values and the environmental quality of public infrastructure.

An updated Green guide to specification from BRE provides greater guidance on the choice of construction materials and includes some aspects of landscape for public realm construction. We need to look in more depth at how we monitor these values and the transport cost of local against imported materials and recycled against manufactured materials.

The same arguments apply to resources within the public space network. Space can be allocated to encourage low carbon forms of travel through facilities such as electric vehicle recharging and cycle hire and parking. Solar or wind power can be used for lighting. And civic space can provide sites for power facilities such as communal energy plants and district heating.

There is a need to review how we use extracted finite mineral sources and transport them, both from the UK and abroad. Carbon footprinting will help establish the whole-life and carbon cost comparison between materials like Chinese granite kerbs and locally produced kerbs made from recycled aggregate. There is definite economic value in supporting local UK-based industries.

A more rigorous appraisal of materials will be required than has been the norm so far. Decisions at both a city and site scale should be informed by whole life or whole quality assessment - not just an assessment of environmental or cost/maintenance performance. For example, some materials may perform well in one respect, such as rainwater permeability to deal with wetter winters, but poorly in another, such as radiant heat reflection in hotter summers. Over a public space’s lifetime the total environmental, economic and social impact should be considered to inform the choice of design and the materials used.

Opportunities to use low embodied energy materials for public realm projects should be considered and promoted during the preparation of design briefs or codes for sites. A whole-life costing approach ensures decisions are based on capital, management and environmental costs of the materials chosen. Priority should be given to materials that reduce embodied energy and carbon costs. Design briefs and guidance should highlight the importance of considering a whole-life costing approach to material choice.

Recycled and low-energy forms of materials can also provide new opportunities for design. In Newcastle the Blue Carpet art project has created a new public space outside the Laing Art Gallery using recycled bottle glass.

Cement manufacture is a major contributor of greenhouse gases, responsible for about 5 per cent of all global carbon dioxide emissions. Cement can be replaced with alternatives such as ground granulated blast furnace slag. Slag can replace cement at rates of up to 90 per cent, with a usual maximum replacement level of 70 per cent. This reduces the CO² emissions of concrete by up to 50 per cent. It is common practice in the UK for ready mixed concrete companies to produce concrete with a cementitious component of 50 per cent slag and 50 per cent Portland cement. Costs are no higher and durability is not compromised.

The performance of materials across the seasons in a changing climate is also important to consider. Research has begun to consider the impact on local microclimates of different pavement material types and colours. Cool materials and colourings for surfaces are now commercially available in both white and non-white forms and have been shown to be at least 15oC cooler than counterparts.

Surface materials should be carefully chosen to minimise absorption of heat in areas that suffer from the urban heat island effect. Studies show whiter pavements reflect more heat than darker or greyer ones.

Studies have also modelled the temperature effects of changing from darker to lighter surfaces in terms of reducing energy spent on cooling and medical and lost-work expenses caused by poor air quality. If urban surfaces were lighter in colour, more incoming solar energy would be reflected back into space, cooling the surfaces and ambient air.

Priority: maximise the potential of public space
Tags: public space, cities and towns, neighbourhoods