Roof-spray cooling systems have been developed and implemented to reduce the heat gain through roofs so that conventional cooling systems can be reduced in size or eliminated. Currently, roof-spray systems are achieving greater effectiveness due to the availability of direct digital controls (DDC). The objective of this paper is to develop a mathematical model for the heat transfer though a roof spray cooled roof that predicts heat transfer based on existing weather data and roof heat transfer characteristics as described by the transfer function method (TFM). The predicted results of this model are compared to the results of existing experimental data from previously conducted roof-spray cooling experiments. The mathematical model is based on energy balances at the exterior and interior surfaces of the roof construction that include evaporative, convective, radiative, and conductive heat transfer mechanisms. The transfer function method is used to relate the energy balances at the two surfaces that differ in amplitude and phase due to the thermal resistance and thermal capacitance characteristics of the roof. The model is shown to yield relatively good predictions of heat transfer rates through the roof. The calculation method shows promise as a relatively simple means of predicting heat gains based on calculation procedures that are similar to those frequently used by practicing engineers.