Energy cost analyses were conducted for both the 2.5 cmand the 5 cm insulation on the green roof, cool roof and traditionalroof to allow for comparison. R-values are additive for materialsin series, allowing us to calculate the transmittance of heat fromthe bottom of the soil through both the concrete and insulation.This additivity allows us to consider the insulative properties ofthe composite design of the roof. A conductance model based on asimple 1-D heat flux equation can be used to solve for the powerrequired to heat or cool the building, as shown in Eq