Assessing sustainable construction

Although assessment criteria are available, there is no robust methodology that can objectively quantify and assess all three dimensions of sustainable construction, i.e. all the environmental, economic and social aspects.

The science of assessing the environmental impacts of construction and buildings is however, relatively advanced and tools such as life cycle assessment (LCA) are available to quantify and manage the environmental impacts of construction and buildings. 

Life cycle assessment

LCA is now recognised as the most appropriate tool to assess the environmental impacts of the built environment. In the UK, the Building Research Establishment has developed an LCA methodology, called Environmental Profiles, for assessing the life cycle environmental impacts of buildings and building products. This methodology is employed in many of BRE’s environmental assessment tools including BREEAM, Ecohomes and Envest. For further information visit the BREEAM website.

All materials used in construction have some impact on the environment but it is how these materials are used to construct buildings and how those buildings perform over their life time, that is the most important factor for achieving more sustainable construction.

A comprehensive building LCA study therefore should include quantification of the following:

• The environmental impacts associated with acquiring the raw material and processing this material into finished construction products. These are called embodied impacts
• The in-use impacts of the building which will include its energy consumption and the maintenance and/or replacement of various parts of the building. These are called operational impacts
• Impacts from the deconstruction and ultimate disposal of the building. These are called end-of-life impacts

Although LCAs can be extremely complex, in simple terms they involve quantification of all the basic inputs to (and outputs from) the construction and operation of a building over a defined timeframe. Inputs include raw materials, energy, etc. and outputs include waste and emissions to air and water. These inputs and outputs are then aggregated to assess different environmental impacts such as global warming potential, ozone depletion, resource depletion, waste, etc.

Recent building LCA studies have concluded the following points that need to be considered when assessing the environmental impacts of buildings:

• It is important to consider the structural efficiency of the materials used. Comparing environmental impacts on a unit weight basis can prove misleading
• For most building types, the operational environmental impacts far exceed the embodied impacts. For example, for an office building with a 60-year design life, the operational impacts exceed the embodied impacts by a factor of between five (for naturally ventilated) and 12 (for air-conditioned)
• The durability of products is important particularly those that will require replacement during the life of the building. For example, a low impact product that needs to be replaced every five years may be worse than a higher impact product that only needs to be replaced every ten years
• Maintenance impacts can be significant over the full building lifetime. High embodied impact products, with a low maintenance requirement may be preferable when assessed over the whole life cycle
• Flexible and adaptable buildings can accommodate change of use more easily therefore extending the life of buildings and extracting greater value from the resources invested in it
• End-of-life impacts such as building demolition and disposal need to be considered. Products that can be reused and recycled when a building has become, redundant have a better environmental profile than those that are simply landfilled

LCA and steel construction

The steel production and construction industries strongly support the use of LCA and have collected and developed high quality LCA data on all common steel construction products. This data can be used in full building LCA studies and has been used in several LCA studies that have been undertaken to understand better how steel can be used to create buildings that have low, whole-life environmental impacts.