The Sustainable Building Material Index (SBMI) is a useful methodology for understanding the nature and scale sustainability impacts associated with a building material and products. The approach is innovative in that it includes socio-economic aspects, which are not included in current building product assessment tools. It however it does not provide the level of detail found in life cycle approaches and level of diagnostic functionality achieved in social or environmental life cycle assessment.
It provides a rapid way of capturing, presenting and comparing key sustainability impacts of building materials. This makes highly relevant for Architects and Clients wishing to support sustainable development. It will also be useful to governments wishing to achieve beneficial social and economic impacts through construction and infrastructure investments.
Building product assessment data
In a developing countries environmental, social and economic data related to building materials may not be readily available or accurate. Environmental databases for materials, such as those used for lifecycle assessment in Europe and the US, also do not exist. Industry-specific social and economic statistics, similarly, may exist or be readily accessible. This means that data used for assessments of building materials must be sourced directly from building material and product manufacturers. Detailed data and calculations are also required to ascertain ecological footprint and human development index impacts (Malmqvist et al., 2011).
Building product manufacturing system
The SBMI therefore uses proxy indicators for ecological footprint and human development impact to make the process of sustainability assessment practical (Hertwich et al., 1997). In addition, a limited set of key sustainability indicators are used in order to ensure assessments can be carried out rapidly and cost effectively. Criteria are generated through an analysis of the building manufacturing industry as a system, with inputs, outputs and social and economic impacts, as illustrated below.
SBMI criteria
This analysis provides a proxy set of indicators shown in the tables below. The first table lists ecological indicators and provides a proxy for ecological footprint impact of building materials. The second table lists human development indicators and provides a proxy for human development index impact of building materials.
Measuring performance of these indicators on a product manufacturing site enables provides an understanding of the sustainability impacts of processes associated with products. A assessment of the impact per building product can also be established. This is calculated by dividing annual ecological or human development impacts of the manufacturing process by the number of products produced over the same time period. This calculation, while useful for measuring sustainability performance of manufacturing processes, does not support comparisons between different materials. This requires the application of the concept of a functional unit.
Functional unit
The functional unit concept was developed within the life cycle assessment methodology to support environmental impact comparisons between products. ISO 14044 defines the functional unit as the ‘quantified performance of a product system for use as a reference unit‘ (ISO 2006).
In the building industry, a functional unit can be described in terms of a ‘final useful constructed elements‘, such as an area of compliant wall assembly. ‘Compliant‘ refers to a requirement for the constructed element to meet specified standards and/or legislation, such as building regulations related to thermal conductivity, structure, fire and water resistance. In this way sustainability impacts can be established, and then compared, for the same functional unit, such as a square metre of compliant wall area, for different material. Sustainability impacts of materials such as bricks and concrete blocks therefore can be established and compared, as the basis of their comparisons (compliant brick and block walls) is the functionally similar. In this way the functional unit supports comparisons of different materials and products (Kellenberger, & Althaus, 2009).
A final stage in the development of the tool is the conversion of impacts per functional unit into a index which supports decision making. The index could consist of values from 0 to 5, with 5 being the worst performance and 0, the best performance. Best performance, or a 5, would be set by establishing targets or required performance for the specified criteria. Required performance targets may differ, depending on the context, with for instance, developing countries setting higher education targets that developed countries in order to promote improvement. Poor performance, or a 0, would be set by establishing the worst performance of currently used building materials. Respective index values between the 0 and 5 would then established by equally spacing intervals between these limits. This enables a report to be generated and an example of this is shown below.
