Previous CIRs have allowed the use of a weighted average approach for the reflectance and for the emissivity of a roof material. A baseline reflectance is calculated by applying the minimum reflectance of the roof (0.65) and multiplying it by the percentage of roof it covers (75%). This calculation results in a baseline reflectance of 0.4875. Similarly, baseline emissivity can be calculated as 0.90 x 75% = 0.675. Can this weighted average approach be used for both of these values simultaneously? In other words, if a roof material covers 100% of the roof area, and its reflectance is 0.4875 or greater, and its emissivity is 0.675 or greater, does it meet the credit requirements? Will the weighted average approach also be allowed as it pertains to a roof\'s SRI under v2.2?
Per the CIR Ruling for SSc7.1 dated 12/05/01, you may perform a weighted average calculation for the reflectivity. Alternatively, you may apply the weighted average for emissivity instead of reflectivity, but not both (it would be too lenient compared to the original credit requirements). The weighted average approach can be used for SRI in NC v2.2. Applicable Internationally.