Towards sustainable homes through optimization: An approach to balancing life cycle environmental impacts and life cycle costs in residential buildings

In this study an optimisation model that is intended to minimise life cycle cost, subject to a set of environmental impact constraints, was put forward as a design support tool that embraces the principles of both inter-generational and intra-generational equity and has the potential to move the residential building industry towards sustainability. A literature review, which laid the foundation for the research, revealed eight key foci of current attempts at sustainable architecture: (i) site selection and building orientation; (ii) material selection; (iii) construction methodology; (iv) energy consumption; (v) water consumption; (vi) waste management; (vii) indoor environmental quality; and (viii) cost. With the aid of a case study, two of the structural components (walls and floors) and three of the envelope components (insulation, windows and cladding) were compared on the basis of six environmental indicators to demonstrate the mechanics of the model. The indicators used were embodied energy, solid waste generated, an air pollution index, a water pollution index, global warming potential and ecologically weighted raw resource use. The life cycle cost for each of the alternatives was also compared. It was found that the structural changes had an overall negative environmental impact at an increased cost and thus were not considered feasible alternatives. Changes to the envelope components produced more interesting results. There were two main conclusions from the case study results: (i) more innovative components are needed in order to improve upon the base house and (ii) operational energy is the main issue that needs to be addressed if lower life cycle environmental impacts are to be achieved at lower costs under prevailing conditions. Thus, energy efficiency in the use phase and the quest for low cost energy sources that have lower environmental impacts become critical. The main strengths of the model are its flexibility and ease of use. The greatest limitation is lack of environmental impact data on (i) more innovative component options and (ii) mechanical systems choices. With the improvements outlined, the full potential of the model as an effective design tool geared towards increased sustainability in the residential building industry may be realised.