Cost model for optimum thicknesses of insulated walls considering indirect impacts and uncertainties

•The Reliability Based Design Optimization provides optimum thicknesses under reliability constraints.•Uncertainties impact significantly on the necessary thickness to be used.•A new proposed cost formulation considers indirect costs and brings up the unexpected difference in cost.•The payback periods show the difference in the time recovery of the investment considering indirect costs or not.

Nowadays, insulation is increasingly used for houses and buildings for its economic and environmental advantages. The performance of an insulated construction depends mainly on the thickness and the properties of the used insulation material. However, this performance is subjected to various uncertainties related for instance to the manufacturing process of the material and to the different workmanship errors that affect the thermal resistance of the insulated construction. In practice, these uncertainties are still rarely considered in energy analysis. Nevertheless, beyond a given level of uncertainties, the insulation system does not perform as expected which induces additional unexpected costs related to energy and pollution. This work aims first, at showing the impact of these uncertainties on the reliability of the insulated construction and second, at developing a new formulation of the global cost for the design of insulation system considering additional costs related to user and environment. The proposed cost formulation allows us to provide a better estimation of the payback period. Three configurations are considered with different insulation schemes in order to show the impact of uncertainties and indirect costs on the insulation performance.