LCA is a technique which assesses the environmental impacts of a building component right the way through its life. It is becoming increasingly important as more and more specifiers are required to consider the environmental impacts of the products and materials they select, taking into account where the material comes from, how it is used or converted into a product and its use in a building, right through to its disposal or re-use/recycling. It considers the impact of a material or product’s use during 3 specific phases:
Please click on each of the phases above for more detail.
Wood and wood products generally have a low environmental impact compared with products manufactured from other materials. Indications suggest that most wood products will score A+ or A in the forthcoming BRE Green Guide.
Production phase
The energy used in the extraction and production of a material or product is called ‘embodied energy’. Generally speaking, the higher the embodied energy, the higher the CO2 emissions. Compared with the high emissions and embodied energy of alternative materials like steel, concrete, aluminium and plastic, wood has low embodied energy and, thanks to the carbon sink effect of the forest, negative CO2
Even when materials like steel or aluminium are recycled, the process often requires huge amounts of energy. By comparison, where the wood industry does require energy, it is one of the highest users of biomass power generation, often making a net contribution to national grid networks. The impact of materials transport is taken account of within the LCA calculation.
In-use phase
European governments are increasingly using legislation to improve the thermal efficiency and reduce the energy consumption of new buildings. This has an impact mainly on the building’s overall envelope performance and is equal for all materials.
However, wood’s natural thermal efficiency means timber systems can be more cost-effective in constructing energy-efficient buildings than cement block, brick or alternative materials. In addition, triple-glazed windows can be more easily produced in wood than in other materials and wood floors will provide better thermal insulation than concrete floors.
It is especially favoured in cold climates, where, with careful design and considered use of insulating materials, low energy consumption reduces heating costs whilst providing comfortable living conditions, often in sub-zero external temperatures.
A Swedish study undertaken in 2001 compared the embodied energy and CO2 emissions from the construction of two similar houses, one made from timber, the other from steel and concrete. The difference of 2 300 MJ/m2 energy used in the materials and construction of the houses is enough to heat one of the houses for 6 years, while the 370 kg/m2 difference in CO2 emissions is equivalent to the emissions from 27 years’ heating – or driving 130 000 km in a Volvo S80.
"Two thirds of energy used in European buildings is accounted for by households; their consumption is growing every year, as rising living
standards are reflected in greater use of air conditioning and heating systems."
EU Commission: Better Buildings: New European Legislation to Save Energy, 2003
End-of-life phase
Wood and wood-based products have unique end-of-life properties. In addition to recycling by-products like sawdust, chips and off-cuts into particleboard, many other panel products are manufactured from recycled wood. However, beyond this, wood is increasingly used as a substitute for fossil fuels, providing a renewable energy source which simply returns to the atmosphere the CO2 it originally removed.
Generally wood products perform well, not only because growing trees absorb CO2, but also because of low energy inputs for processing and good thermal properties in use. Taking care over efficiency of use and disposal can reduce the impact of landfill and improve LCA results. For details on recycling schemes visit www.recyclewood.org.uk
