Energy conservation in buildings is becoming an issue of great importance. Space cooling is getting important in most countries and different techniques have been developed one of which is radiative cooling. A prototype roof component, exploiting radiative cooling, was built and tested in the outdoor test facilities of the Centre of Renewable Energy Sources in Greece. The component comprises a radiator, which is utilizing water as the fluid medium and its cooling performance was investigated. This paper presents the construction of the component, the experimental set-up and the results taken during the monitoring procedure. (c) 2005 Elsevier Ltd. All rights reserved.