The construction process itself generates significant quantities of waste: about a fifth of all waste arisings are attributable to the construction phase. This waste is generated at every stage in a normal construction project, from initial winning of resources such as aggregate, through processing, packaging, transport, use on site, repair and disposal.
A significant portion of these arisings can be designed out of a project with careful selection of materials. For example, a steel frame building generates waste from ore mining, processing, transport and smelting before the foundations are laid but a timber frame building carries no such environmental burden. However, it is important to give careful consideration to such decisions and to avoid sweeping assumptions. If the steel is manufactured from scrap, as a large proportion is, then there is a net reduction in waste (although there is still a considerable energy burden) and timber sourced from unsustainable forestry practices can have a dramatic detrimental effect on biodiversity. For any particular material, there is often a wide variation in the environmental impact of production by different manufacturers. It may therefore be necessary to assess the environmental performance of a number of potential suppliers. Reduction of waste arisings at this stage is dealt with in the materials section.
Waste and environmental pollution from transport of materials to the construction site can be minimised by specifying local producers wherever possible. This also makes it simpler to check up on the environmental performance of suppliers and provides a useful incentive for prospective suppliers to demonstrate their environmental credentials, as their products may then be specified for subsequent sustainable construction projects in the area.
The reduction of environmental impacts from the construction process itself requires an additional level of control over all aspects of construction. One useful way of addressing these issues is to consider the construction project in exactly the same way as any other manufacturing or production process and to apply the principles of waste minimisation on this basis. A typical waste minimisation project of this sort would consider the inputs, processes and outputs of the production process, as well as any utility inputs such as energy, water etc. One difficulty with applying these principles to construction is that each project is unique, which can lead to problems when assessing the effectiveness of a waste minimisation approach. However, if the right measures and benchmarks are chosen, these difficulties can be overcome.
The efficiency of a construction project is usually measured only in terms of cost per square meter. This measure is something of an over-simplification but it does provide a useable foundation for other measures which can be compared across projects. Floor area provides a somewhat crude but nonetheless useable denominator with which a single house can be compared with a housing estate, or an office block. However, it does not allow comparison of a house with a bypass, for example. Such comparisons require an agreed standard of environmental performance across the various divisions of the construction sector. This standard does not yet exist but there are already visible moves toward it in accreditation schemes such as BREEAM.
For the purposes of sustainable construction as it exists today, comparison between these divisions is not important. If the construction of one house can be reliably and meaningfully compared with another house, this will represent a significant milestone. Using floor area as a denominator, it should therefore be possible to develop useful indicators of performance, which can then be used to manage and reduce waste arisings from construction. These might include:
embodied energy / m2
total transport mileage / m2
energy used during construction / m2
waste generated during construction / m2
Other indicators might include:
percentage recycled material by weight
energy efficiency of completed building
Gathering and analysing information that would normally be overlooked reveals trends that show the potential for cost savings and for reductions in the environmental impact of construction activities. An example is the proportion of waste generated on site that has not been used. Waste arisings from construction include off-cuts, packaging and other legitimate wastes but also include material which has simply been spilled, dropped or run over before ever being used. Indeed, some of this material never even makes it into the skips: sand, for example, is often seen in large, spreading mounds with tyre tracks through it. Once a waste of this kind has been identified, steps can be taken to address the issue. Specification of pre-mixed mortar removes the requirement for sand and simultaneously leads to an improvement in quality. Similar examples of cost and environmental savings are found in the project examples and more will be added to the site as they arise.
More information is available from www.sustainableconstruction.co.uk