This paper analyzed the energy balance of extensive green roofs and presented a simple but practical energy balance model. Field experiment justified the validation and accuracy of this model. Experimental results demonstrated that within 2411 of a typical summer day, when soil was rich in water content, solar radiation accounted for 99.1% of the total heat gain of a Sedum lineare green roof while convection made up 0.9%. Of all dissipated heat 58.4% was by the evapotranspiration of the plants-soil system, 30.9% by the net long-wave radiative exchange between the canopy and the atmosphere, and 9.5% by the net photosynthesis of plants. Only 1.2% was stored by plants and soil, or transferred into the room beneath. (C) 2010 Elsevier B.V. All rights reserved.