Life Cycle AnalysisThe concept of life cycle analysis – also known as “cradle-to-grave” analysis is hugely important to all disciplines of environmental thinking, including green building. It considers the full range of environmental consequences – good or bad – assignable to materials and resources, caused by its entire existence. This includes the creation, extraction, processing, transportation, use and disposal of a product. The item’s environmental “footprint” is considered on balance – almost all products will reveal positive and negative traits upon complete examination.
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Coal makes a good example of a resource with negative environmental impacts throughout its life cycle: coal mining has disastrous consequences just as the combustion of coal. Many products may seem harmless to manufacture and use, but are not biodegradable and clog landfills as waste. Nuclear energy may seem relatively safe and benign until consideration is given to the radioactive waste that cannot be disposed of.
A recent concept of “cradle-to-cradle” takes an additional step and considers the re-use of a material or product after its initial use is complete.
A good example of life cycle thinking related to green building is to consider wood, a very common building material. Wood is a natural and renewable material, and it is biodegradable. It is important to consider the source of the wood – it may come from well-managed, sustainable forestry practices, or it may be extracted through ruinous land- and habitat-destroying logging operations. It may even come from a threatened rain forest. Certification programs are in place that enable consumers to purchase wood only from responsible suppliers.
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Harvesting, processing and transporting wood uses energy resources. The more processes the wood undergoes in creating a product, the lower the positive benefits of wood from a life-cycle analysis point of view. Many wood products use adhesives and chemical treatments that can be toxic and problematic. Wood is a product of which the waste of its manufacture – trim waste, sawdust, and the like. -- can be used to make other products (particle board, for instance) or burned as fuel, for energy.
Wood comes from trees, of course. Trees and all plants are beneficial as living things -- acting as the earth’s “lungs”, they take carbon dioxide (a greenhouse gas) from the atmosphere, and give off oxygen. For as long as the wood exists, living or not, a quantity of carbon is contained and “lock in”. The carbon is eventually released back to the atmosphere, either through bio-degradation (rotting in a forest or a landfill) or burning. In the case of burning, the wood may be used as a renewable biomass energy source, fueling boilers that provide power.
It is important to consider that the carbon released to the atmosphere by wood is carbon that was taken from the atmosphere in the first place, so the net carbon “footprint” on the atmosphere is essentially zero, on life-cycle balance. Compare to a fossil fuel resource, where carbon is unlocked from permanent storage deep in the earth, and inevitably ends up in our atmosphere.
Considering the carbon that is locked in to the wood used to construct an all-wood building can inform us that the building may be operated (heated, cooled and illuminated) for years before its net, life-cycle carbon footprint climbs above zero!
“Cradle-to-cradle” thinking emphasizes the planned re-use of a material at the end of its first useful life. Extremely green buildings can be planned to use reusable materials installed in ways that are easily disassembled for re-use in newer buildings or otherwise. The re-use of timbers from older building frames to make newer buildings is a standard and age-old practice based only on cost-savings, that illustrates “cradle-to-cradle” thinking by giving the material a new life.