Whole-life costing and life-cycle assessment are both becoming more common in the construction industry, the former to analyse the economic cost of a building, the latter its environmental impact. This article seeks to show how they can be used together to improve a structure's sustainability, with three recent case studies.
The two tools were developed to address different concerns, but they have much in common. Both analyse the following stages in a building's life-cycle: production of components, construction, repair, maintenance and replacement, demolition and recycling. Life-cycle assessments also consider the extraction of raw materials. Both use data on quantities of materials used, the service-life of the materials, the maintenance and operational implications of using the products, and the end-of-life proportions to recycling (and sale value) and disposal.
The key difference is that whole-life costs do not consider the process of making a product; they are concerned with the market cost. Life-cycle assessment does consider production. Also, whole-life costing is usually discounted to present value over time; environmental impacts are not.
Life-cycle comparisons and the Ecopoint system
Comparing the whole-life cost of buildings is relatively simple, but it has been less easy to make environmental comparisons because of the wide range of data available. To simplify the process, in 1998 the BRE developed a scoring system for environmental impacts, known as Ecopoints.
Based on the Methodology for Environmental Profiles of Construction Materials, Components and Buildings, the system covers the extraction, processing, manufacture, transport, use and disposal stages of a product's life-cycle. A profile summarises the environmental impacts arising from these stages into 13 categories, including climate change, atmospheric and water pollution, and raw materials consumption. Some of these categories have a greater overall impact than others, so to calculate the Ecopoints score, each is multiplied by a weight that reflects its importance. The weightings were developed after consultation with the public sector, construction materials producers and manufacturers, property professionals, environmentalists and academics. Ecopoints are based on UK-generic figures and manufacturers can obtain Ecopoints for their own brand. The system was devised so that the annual environmental impact caused by a typical UK citizen is 100 Ecopoints. A higher score means higher impact. The system is used in the case studies overleaf.
These studies examine three situations where a combined approach to whole-life costs and life-cycle assessment data has usefully aided the design process. In each case, the same service-life and specification have been used for the whole-life costs and the Ecopoints score. This ensures consistent comparison. Two of the studies are PFI schemes; the third presents a design team working for an owner-occupier that has a commitment to procure a state-of-the-art sustainable office building.
Study 1: Kvaerner's PFI hospital bid
Kvaerner Construction was invited to tender for a new hospital building by an NHS trust. As part of the bidding process, Kvaerner carried out whole-life costing of key elements of the building. Early investigations, in conjunction with the BRE, demonstrated potential whole-life cost savings of 5% on the 30-year service period.
The client output specification required Kvaerner to demonstrate its approach to "green building principles". So Kvaerner combined whole-life costing and life-cycle assessments. The graph, right, shows the whole-life cost, expressed as a net present value, and the environmental impact of two options for the internal walls. These are:
In this case, the cheapest option also had the lowest environmental impact. The life-cycle assessment results therefore served to reinforce the choices identified by whole-life cost analysis and the client was reassured.
Study 2: Choosing materials for Swindon's Princess Margaret Hospital
Carillion is lead partner in the construction of the PFI Princess Margaret Hospital in Swindon. It has used both whole-life costing and sustainability information to develop the materials specifications. Targets have been set for lifetime savings of 30% in CO² emissions and 50% in waste generation.
Carillion analysed a number of building component options to investigate the potential for whole-life cost and environmental savings on future buildings. One of these options was to improve the insulation of the building envelope. It found that a 50% improvement of the roof insulation provision above the design brief would cost £21 000, but save £27 000 on the capital costs of radiant appliances on the top floor and £213 000 in running costs over the building's life. Having finalised the building design based on this financial case, Carillion was keen to investigate complementary environmental data to this costing information.
The environmental impacts of different U-value options were investigated using Ecopoints. The type of insulation is important for the Ecopoint score, so both polyurethane and mineral wool insulation were modelled for the walls, roof and floor (table, right). The building was assumed to have mechanical ventilation, which has an impact on heat loss figures. In order to achieve a U-value of 0.22 W/m2ºC – half the U-value for roofs in the Building Regulations – the thickness of insulation was roughly doubled in each element of the building.
The exercise showed how the heat lost through the building envelope can be reduced by about 17 000 Ecopoints when the U-value is decreased. The number of Ecopoints embodied in the building envelope rose as extra insulation was used in the model, but the overall Ecopoints for the building over its lifetime decreased for both insulation types.
Carillion has benefited from a structured approach to obtaining sustainability information from materials suppliers. The company collected information direct from manufacturers, which produced wide-ranging, qualitative data to assist in the selection process. This approach is allowing Carillion to optimise the costs and environmental performance of the design options available.
Financial management arrangements need to be flexible to allow the benefits from trade-offs between embodied and operational performance to be realised. Carillion has achieved this within the constraints of its PFI project. However, further effort is required to overcome the deeply ingrained business culture that compartmentalises capital and maintenance funding which is more difficult to overcome on traditional projects.
Study 3: Wessex Water's "green" headquarters
When Wessex Water commissioned a new operations centre in Bath, it wanted state-of-the-art sustainable construction. Architect Bennetts Associates and cost consultant Davis Langdon & Everest were required to ensure that the design of the structure and the materials fulfilled the client's brief.
Detailed whole-life cost assessments of building elements were carried out by DL&E. The BRE provided environmental assessments of the same elemental options and worked closely with DL&E to ensure that the same quantities and lifetimes were being considered. The environmental assessment results were presented in the form of Ecopoints.
Selecting the floor and ceiling finishes provided an example of the application of whole-life cost and life-cycle assessment comparisons. On comparing Ecopoints for ceiling and floor finishes, it was clear that more overall environmental impact occurs from the floor finishes than ceiling finishes. In fact, synthetic carpet backing alone was found to have higher Ecopoints than some ceiling finishes. This led the designers to evaluate three further carpet backing options for reduced environmental impact. The single score was usefully combined with whole-life costing data. The simplicity of the rating also allowed the design team to appreciate the significance of making this particular effort.
The benefits to Bennetts Associates, and Wessex Water, have included making design decisions based on consistent environmental information; and improving the efficiency of the design process by identifying design decisions with the greatest environmental impact and which will yield greatest benefits from further investigation of procurement options, within a specified budget.
Downloads
How the two wall options compared
Other, Size 0 kbEnvironmental comparison of floor finishes
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Postscript
For more details on whole-life costing, see www.wlcf.org.uk. For life-cycle assessment, see www.bre.co.uk/envest
