1st November, 2009 - Posted by admin - Comments Off
Professor Geoff Hammond and Craig Jones of Bath University produce the Inventory of Carbon & Energy (ICE), an inventory of building materials giving their embodied energy and carbon dioxide. It is a very useful resource. But NoHighBuildings takes issue with the methodology they choose for assessing recycled materials. It is the recycled content approach. They say
Using the recycled content approach the incoming metals to the building could be split between recycled and primary materials. If this gives 40% recycled metals then the recycled content is set at 40%. This is a start of life method (i.e. start of life of the building) for crediting recycling. Using this method the materials entering a building takes the recycling credit (thus upstream of the building/application).
This approach is particularly relevant to metals. This approach may be compared with their treatment of the carbon footprint of timber. They do not count the carbon held in timber for it’s lifetime. They quote a paper by A. Amato “A comparative environmental appraisal of alternative framing systems for offices”. This paper says
In measuring embodied CO2, what is being sought is the CO2 burden to society which consequent upon society’s use of a particular material. The deduction of a CO2 value sequestered by the material during its manufacture from the total embodied CO2 burden is not appropriate just because a material is deemed renewable and is surely only appropriate when a world wide steady state has been achieved between consumption and production.
This alludes to the fact that if a new building uses timber from renewable sources, it diminishes the stock of renewable timber so that other buildings will need to use timber from non-renewable sources. But precisely this argument can be used for recycled steel or aluminium. Until all consumption is sourced from recycled metal, any extra that is used causes the production of virgin metal somewhere in the world.
On this score the footprint of BedZED (See Embodied carbon ignoredEmbodied carbon ignored) will be even greater than 675 Kg CO2e per square metre of floor space (see below in topic “Embodied carbon ignored”).