Approaches for the assessment and improvement of performance of antisolar surfaces

Solar reflectance and thermal emittance are key parameters to evaluate the solar heat gains through opaque building elements. A high solar reflectance allows building surfaces to minimize absorption of solar energy, whereas a high thermal emittance allows returning to the environment most of the solar energy that is however absorbed by any actual surface. Therefore, summer overheating of buildings can be prevented by selecting external coatings with proper values of both properties. In this work, the role of radiative properties is explained in quantitative terms and standard test methods for their measurement are briefly presented. The behavior of some typical cool roof surfaces is then analyzed, in order to point out the limits of qualitative selection criteria and demonstrate the need of quantitative approaches to enable product comparison and development. Eventually, the perspectives offered by the use of advanced materials and coatings are also highlighted.