A radiative cooling system consisting of unglazed flat plate radiators, water as heat carrier and a reservoir is presented. The radiators are twin-wall sheets made of a modified PPO (polyphenytenoxid) resin, which are proposed as low cost roof integrated modules. The thermal performance of a system with a radiator aperture area of 5.3 m(2) and reservoir volume of 280 l has been investigated in experiments for Oslo climate. A parameterisation for the cooling performance of a tilted radiator surface for clear and cloudy atmospheres is proposed and applied to model the experimental results. The impact of the tilt angle, the aperture area and the reservoir volume on the cooling performance has been studied in simulations. The feasibility of a radiative cooling system designed for a single-family house at southern latitudes has been modelled. Except for mid-summer ambient temperature and high relative humidity, the simulations show that the radiative cooling System seems to cover the demand. (C) 2003 Elsevier Science Ltd. All rights reserved.