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Cities are Built of Steel and Cement. How Can We Make These More Sustainable?

Without concrete, stone, metals and plastics there would be no cities. It follows that sustainable cities should use materials efficiently.

Sustainable Materials Without the Hot Air coverEverybody knows that we use raw materials inefficiently but there are great knowledge gaps in what to do about it. There is much talk of the "closed loop" economy and these days, at least in Europe, the term "resource efficiency" has gone some way towards replacing "waste management" because it sees waste as a resource not as something to be disposed of.

But the authors of Sustainable Materials Without the Hot Air, Julian Allwood and Jonathan Collen, want us to go further upstream. They want us to look in detail at the production of materials and then to crunch numbers to figure out what is the most effective way to reduce their environmental impact.

The subject is incredibly complicated but the authors adopt a forensic and systematic approach to simplify it for us. They want us to concentrate our efforts where it matters most which, in terms of materials efficiency.

It turns out, for example, that we should not be worrying about plastic bag use (responsible for less than one hundredth of a percentage point of national greenhouse gas emissions) so much as on industrial emissions, i.e. those connected with materials production, which comprise 35% of all energy/process greenhouse gas emissions. That's more than buildings (31%) and transport (27%).

Of industrial carbon emissions, the single material responsible for the most emissions is steel production (25%), followed by cement at 19%. Combined, that's nearly half of all industrial emissions, and bear in mind that these two are the principal materials for building city infrastructure.

So anyone with an interest in reducing greenhouse gas emissions from cities should pay attention.

The authors identify a further three priority materials for action: plastic, paper and aluminium, making this decision purely on the basis of associated carbon emissions.

They begin by examining the standard ways to save energy in the production of cement and steel such as with energy efficiency, recapturing process heat, developing new process routes, carbon sequestration and renewable energy use. They then go on to look at more fundamental issues such as designing for minimal material use, for end-of-life reuse, and options for reducing demand and encouraging circular processes.

The book is a revised edition of the same authors' Sustainable Materials With Both Eyes Open published in 2012, which I also happen to have. Its new name is clearly intended to ride on the success and popularity of David McKay's highly recommended Sustainable Energy Without The Hot Air. The books aren't quite the same though. Whereas McKay's is clearly aimed at consumers as well as policymakers and is utterly comprehensive, I believe the title for this new book to be misleading because it does not cover all materials and because it is not comprehensive in its approach, partly for the reason explained above.

Briefly comparing the two editions I cannot see a great deal of difference apart from the addition of a short chapter which critiques progress since the first edition and offers some case studies.

This brings me to my quibbles, which must be kept in proportion to the overall worth of this book, yet illustrate the disadvantages of this focused approach upon only the five (and principally the two main) materials, and only upon one criterion of sustainability, i.e. related carbon emissions.

Firstly, I would have thought that any discussion of cement and concrete would include reference to sustainable alternatives such as hempcrete (not mentioned at all), and secondly to the benefits of using materials which lock up atmospheric carbon in the body of the building, such as timber products. People are already building high-rise structures of timber frame, which is a great way to not use carbon-intensive cement and steel and substitute carbon-negative materials.

In this respect I expected the section on I-beams to include timber I-beams, which it does not. Timber does not appear at all in the index, and neither does hempcrete.  There are also plenty of other indicators of sustainability besides carbon emissions which could be factored in to decision-making.

Anyone relying exclusively on this book for pointers to sustainable building materials would be misled. Since potential readers might be expecting a book with the title Sustainable Materials to point them to substitutes for materials with high environmental costs, this is a serious oversight.

This is despite the fact that the book makes a noble attempt to make its content relevant to decision-makers depending upon what professional practice they are engaged in, such as product designers, manufacturers, industry specialists, retailers, accountants, etc.; the penultimate chapter explains which parts of the book would be most relevant to them.

Really, the book should be titled: Sustainable Steel and Cement. It would still make a huge contribution to the field.

Nevertheless, the book's main message, build more with less, should be heard by everyone.

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David Thorpe is the author of 

His book Passive Solar Architecture Pocket Reference Book is due out in the autumn from Routledge.