In recent years, various passive methods have come to be adopted in architecture design. The rooftop lawn is seen to have merit in the reduction in the air conditioning load of the building, as well as contributing to the mitigation of the heat island phenomenon. The roof spraying system is seen to be an effective method for the roof of low heat insulation performance, and can greatly reduce the heat load in the summer season. However, at present most of the buildings with an RC construction have the insulating material in the roof for providing thermal insulation in the winter season. There has been a trend to adopt the roof spraying system actively in even such a general RC building, but it is not clear how much actual effect it has. In this study, the authors conducted a measurement in an RC building with a rooftop spraying system and roof lawn in order to clarify the effects and problems on the thermal environment. (C) 2004 Elsevier B.V. All rights reserved.