Optimization of a Combination of Thermal Insulation and Cool Roof for the Refurbishment of Social Housing in Southern Spain

Social housing built in the middle of the last century in Spain suffers from poor thermal insulation conditions that cause situations of discomfort and energy poverty. For this reason, the energetic refurbishment of the envelope of this social building stock is necessary to overcome these situations and reduce energy consumption aimed at achieving interior comfort for its occupants. The goal of this work is to optimize a constructive solution that combines cool roof techniques with the use of thermal insulation applied to the refurbishment of the roof of buildings belonging to a quarter of social housing in Seville, Spain. The optimization analysis is based on the computation of the energy performance of the roofs when the energy retrofitting measure is applied, considering a variety of combinations of solar reflective coatings and insulation layer thickness, performing a dynamic analysis that accounts for the aging effect of the cool coats on the monthly roof energy performance and on the economic balance for the whole life cycle (LC) span. Economic and energy optimization analysis show that a suitable combination of cool roof emissivity and insulation layer thickness produces significant savings in the operational energy and in the economic profitability of the proposed retrofitting measure: the optimum combination obtained provides for the entire life cycle timespan an energy savings of 5.71 GJ/m2 and a cost savings equivalent to the 63.1% of the total costs when compared to the non-refurbished roof. The application of a time-dependent pattern for the changes on time produced by the aging effect on the cool roof emissivity, and its effects on the optimization of the combination of cool roof and insulation layer, can be considered novel in literature, both from an energy and an economic point of view.