A new experimental apparatus. "Cold Plate", was designed and built to quantify heat and mass transfer processes for green roof samples inside an environmental chamber. The "Cold Plate" apparatus addressed shortcomings in the existing data sets available for green roof energy balance calculations. Experimental data collected in this apparatus show that evapotranspiration controlled the intensity of all other heat fluxes, depending on the plant and environmental conditions. Also, under the described laboratory conditions, the uninsulated green roof samples with plants showed an average heat flux reduction of 25% compared to samples without plants. This reduction was due to the plants providing extra shading, additional water storage and better water control mechanisms. (C) 2011 Elsevier Ltd. All rights reserved.