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Green specification

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TECHNICAL

The best green specification guide so far in the uk - probably.

Launched yesterday by Construction Minister Nick Raynsford, the 'Green Guide to Specification' is the second edition of a document that began its life within the Post Office as a guide to specifying its own buildings. It is now jointly authored by the Post Office, bre and Oxford Brookes University.

The guide is special in several ways: it is based on a very wide range of measured data; it presents comprehensive range of elements - walling, flooring, etc - on a common scale for ready comparison; and it strikes a user-friendly, pragmatic balance between the over-complexity of looking at every environmental particular and the over-simplicity of a black-list.

The common scale is:

toxicity (in manufacturing, in combustion)

primary energy

emissions (CO2, VOCs, Nox, SO2)

resources (minerals, water, oil feedstock)

reserves

wastes generated

recycling (percentage of recycled materials contained, percentage capable of being recycled, percentage currently recycled in the uk, energy required to recycle)

percentage cost range (£/m2)

replacement interval (years).

For every type of building element, eg external walls, there is a table of 20-30 construction options. Each are rated against the scale above, but simply, as A (best), B or C (worst) in terms of environmental impacts (see illustration). And by drawing together various interest groups from the industry, the authors have obtained consensual weightings for combining the items on the scale to arrive at an A-C summary rating for the construction option overall too.

Inevitably, some of this has to be taken on trust, but there are explanations to guide the specifier. The first help comes from the structure of the document, organised by types of element into:

high-mass elements (external walls, roofs, upper floors)

medium-mass elements (internal walls and partitioning, windows)

low-mass elements (wall insulation, roof insulation, floor surfacing, floor finishes and coverings, doors, paint systems, suspended ceilings and ceiling finishes)

Broadly, mass is the key. The designer's priority is to focus on the high-mass elements. But that is not universally true. Allowance has been made for 'functional units', ie that, say, a tonne of masonry does not have the same walling function as a tonne of steel. (Where needed for comparison, a four-storey office is assumed to define the functions.).

Each element table is prefaced by explanatory notes on the element's relative environmental importance in the building and on why particular construction options rated well or poorly. Comparisons were made for a 60-year building life, allowing for cycles within this of repair refurbishment and replacement.

The authors point up various areas missing from the guide, eg substructure, or clearly lacking information, eg paints. They also point to the need for revision every few years. A very useful piece of work in progress.

'The Green Guide to Specification - an Environmental Profiling System' for Building Materials and Components. Nigel Howard, David Shiers, Mike Sinclair. BRE. From CRC 0171 505 6622. 48pp. £35; launch price £28.

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