LCA benchmarks in building's environmental certification systems

The paper deals with the definition of reference values (benchmarks) referred to the Life Cycle Assessment (LCA) indicators used in the environmental certification systems of buildings (Green Building Rating Systems, energy-environmental certifications and environmental labels) highlighting their potentiality and criticality. The environmental certification systems more and more often consider the use of indicators based on LCA methodology which allow to draw attention to environmental performances of building in terms of impacts during the whole life cycle, from the raw materials extraction to the disposal. Today, the environmental impact measure obtained, could be interpreted through the comparison between similar solutions, due to the absence of thresholds which indicate the eco-efficiency of buildings: the benchmark applied to the LCA indicators becomes the threshold value through which measure the real environmental performance of the object analysed. It is a variable value because it depends on the evolution of technologies and construction practices. The environmental certification systems are the first ones which develop a process to define benchmarks because they have to assign a rating score to the indicators in order to obtain the certification. Through the analysis of principal certification systems, characterized by the use of LCA methodology within the score criteria, the different benchmarks methodologies (related to the LCA indicators) are identified and explained. Benchmarks are typically developed through linear interpolation systems, statistical analysis or the modelling of a reference building. In particular the analysis refers to the Green Building Rating Systems (GBRSs), such as DGNB, LEED, and BREEAM, and the energy-environmental certifications (Minergie-Eco). It is showed how the benchmark, into the certification systems, assumes different meanings: it could be the starting standard value (reference value), or the improvement value (target value) or the minimum value to obtain the certification. Starting from these differences and peculiarities, the paper demonstrates potentiality and criticality of the methodological approaches used, in order to understand the role of benchmark in the development of new policies and environmental strategies.