Normalized Total Global Cost for environmental sustainability assessments: a BIM approach

The design of the energy efficiency of the building stock requires an interdisciplinary approach oriented to the optimization of the integration of building fabric, building services and on-site renewables energy sources (called “fabric/plant/renewables” system) in order to achieve the performance standards NZEB. Optimization can be referenced to the Total Global Cost of intervention which evaluates not only the cost of initial investment, but also the benefits in terms of operational energy savings, as well as maintenance, replacement, disposal costs and possible residual value of assets at the end of the life cycle of the construction. In addition, more and more frequently the project actions have to be compared with the general goals of environmental sustainability. This paper introduces an evaluation method based on an indicator defined from the authors: the Normalized Total Global Cost (NTGC) with respect to the environmental sustainability scores, as calculated in accordance with the methodology of Protocollo Itaca. This approach has been tested on a case study located in Gioia del Colle (Italy), a single-family house built in the '70s,. Different intervention solutions were proposed, which were compared both in terms of reduction of energy requirements and greenhouse gas emissions, both in terms of NTGC. The results have demonstrated the utility of BIM approach not only as part of expensive energy evaluations, but especially with regards to the more complex performance analysis scenario required from Protocollo Itaca. The NTGC, therefore, could be an indicator of economic sustainability for comparative analysis of several design solutions applicable to the design practice. This paper highlight the importance of the BIM approach as an incentive to the application of integrated performance-based design methods. However, BIM systems still require a significant development in terms of implementation of design methodologies and performances verification for sustainability evaluations, especially with regard to the encoded national methodologies.