Optimal Energy; the twenty year house?

22/07/2010

We face ever-increasing pressures on finite global resources due to the rise of the throw-away society and a growing world population. We need more than ever to embrace both recycling and reuse, but are we recycling in the most sustainable way, or just the cheapest? What can the ‘make-do and mend’ mindset teach us about the future of the construction industry? James Thomson, a structural engineer with international engineering consultant Buro Happold offers some interesting ideas.

An aversion to waste comes most strongly to the public consciousness whenever threat infuses a society with need. In such times our ability to extract the maximum utility from our resources is magnified. This is apparent throughout history, not least in the rates of industrial recycling in the USA and UK catalysed by the Second World War when they peaked at levels both countries have struggled to match since. In the face of population growth and an impending resource crisis it is reassuring to note that one of the key tenets of global sustainability is as old as civilisation itself; ‘how do we do more with less?’.

Leaving nothing to waste

Waste averse societies emerge in the poorest parts of the world where necessity becomes a powerful driver towards efficiency. In Cairo's slums the Zabbaleen community process and sell the city's refuse with a rate approaching 90%; a figure worth comparing to San Francisco's aspirations to achieve a recycling rate of 75% by 2020. When there is global identification of a gathering resource crisis, 'doing more with less' might be aspirationally redefined by the globally conscious engineer as 'doing the most with the least'.

The built environment is a major part of per-capita energy consumption and almost every component of the buildings we create derives their embodied energy from fossil fuels with gas fired brick-kilns, coal-fired cement kilns and iron smelting works creating the raw materials which form the basis of modern construction. Driven on by hefty landfill taxes, recycling in the UK construction industry is increasing, but this news must be cheered with caution. The recycling industry is not philanthropic, but a lucrative business which can mean that profit making takes precedence over sound sustainable processes.  Recycling is not inherently sustainable.

The wrong recycling?

Energy degradation of materials during recycling is critical. Bad recycling is like burning a walnut table for fire-wood; technically reuse but not to its greatest potential. UK landfill taxes provide an impetus for recycling which often ends up rewarding cheap untenable recycled outputs rather than efficient re-use. Finding the cheapest end product to make from construction and industrial 'waste', thereby avoiding disposal charges, means that much of the UK and Europe’s recycling is concentrated in processes that convert high-energy materials into low-energy outputs e.g. reducing concrete (high-tech, high embodied energy) into crushed rubble for road construction (low-tech, but still high embodied energy). In this process, energy is lost, entropy increases and we degrade our valuable available resources.

Energy efficient reuse of concrete at anything like its true energy value is impossible as its chemical formation of complex bonds cannot be efficiently reversed to the original value. Compare that to a ton of steel which can be melted down, re-worked, rolled and made into a new beam with an energy consumption of around 65% that of new steel. Of course, in reality the most energy efficient solution is to re-use rather than recycle. With careful design and an eye to the future a bolted steel building frame can be 'deconstructed' rather than demolished and its components re-used with negligible input of energy.

The lifespan of a building

Many modern buildings have a design life of fifty years, indeed it isn’t uncommon for an engineer to see a building they have worked on demolished within the first half of their career. As the Pantheon, the Coliseum, and Hagia Sophia in Istanbul show, concrete structures can last for millennia. We invest huge quantities of energy in concrete construction, a resource investment which rarely pays off in utility.

There is an argument that says we build structures to be too permanent, or at least fail to optimise buildings for their true design life. The change over the last century in the UK from a manufacturing to a service based work force means that we need far fewer factories but more office space. New needs entail renovation or frequently the demolition of building stock. With every demolition of a building conceived without thought for its reuse, great quantities of embodied energy are thrown away.

To do more with less we have three options: to only use construction materials which can be efficiently re-used or recycled, to use materials which in the first place have lower embodied energy or to accept that our society has a propensity for the new and design buildings with shorter design lives. We should, of course, do all three, and recent explorations of new building concepts in Birmingham point to some intriguing possibilities.

New(s)paper projects

In a bid to demonstrate the potential of low-energy materials, the Paper Project set out to demonstrate the construction potential of waste by creating a five metre tall structural prototype made entirely from recycled newspaper. Engineering ingenuity was harnessed to the inherent strength of the material to demonstrate that things our society routinely regards as waste have great potential for the built environment.

Newspaper, when rolled into struts, behaves very much like bamboo, a material used to create some incredible structures in Columbia. Both materials are very strong in axial compression and tension but poor when subjected laterally to other forces. Similarly, the poor durability of bamboo (and newspaper!) requires a system of weather protection or its use in internal locations to render it as a practical contender.

Newspaper is already re-used in the construction industry as cellulose fibre insulation but the possibilities for structural use merit consideration. Lessons abound in Columbian vernacular architecture where bamboo houses were proved safer and more durable to concrete equivalents in the devastating 1999 Columbian Earthquake. The ductility of bamboo meant that low-rise structures swayed rather than broke and softened rather than cracked. Composite panels of thick rolled newspaper sections, rendered for weather proofing could provide lightweight, sufficiently durable and low cost alternatives to cement-based constructions.

Just enough energy to perform

Companies such as Buro Happold are already exploring the possibilities inherent in cardboard construction. For their Japan Pavilion at the Hanover Exposition in 2000, cardboard tubes were formed into a large gridshell. The structure was intended to be temporary and its required design life was duly matched to an appropriately durable material. In the UK, Buro Happold’s work on the Westborough cardboard school in Essex has demonstrated that cardboard construction can provide high-quality, economic, medium life buildings that fulfil a need with an appropriate investment of embodied energy.

Our society can often obsess about ‘building to last’ when in reality style dictates that we buy clothes for a season, a mobile phone for a year or create a building for a decade's use. If we can't change society to a less 'throw-away', consumerist culture, perhaps we can address these short shelf life needs with more appropriate raw materials. If we can learnt to design appropriately, and accept that a rapidly changing society only needs a given building form for a decade or two, then as a global society we open up a huge number of low-energy building materials which really will enable us to do ‘more with less’. This really is just the beginning…