Cool Roof coatings cannot be included in the U value calculations of any building. Coatings, which are applied at .5mm or .7mm thickness, has very negligible R value to function as an insulation.
Cool Roof coatings work on a completely different principle. Solar Reflective Index (SRI) of a coating is a clear indicator of how much Solar Heat Gain (SHG) can be reduced. Higher the SRI, Lesser the SHG.
Solar Reflectance Index
The Solar Reflectance Index (SRI) is a measure of the roof's ability to reject solar heat, as shown by a small temperature rise. It is defined so that a standard black (reflectance 0.05, emittance 0.90) is 0 and a standard white (reflectance 0.80, emittance 0.90) is 100. For example, the standard black has a temperature rise of 90 deg. F (50 deg. C) in full sun, and the standard white has a temperature rise of 14.6 deg. F (8.1 deg. C). Once the maximum temperature rise of a given material has been computed, the SRI can be computed by interpolating between the values for white and black.
Solar reflectivity expresses the degree to which a roof reflects the visible, infrared and ultraviolet rays that comprise solar energy. Surfaces with high solar reflectivity reflect more infrared and ultraviolet rays.
Infrared emissivity refers to the roof's ability to give off its absorbed heat. Highly emissive surfaces are cooler than non-emissive surfaces since they have the ability to shed more absorbed heat at a faster rate.