In this paper, the thermal performance of a ventilated roof component is investigated during the winter period. The ventilated roof component consists of a conventional roof structure-reinforced concrete with a layer of thermal insulation-an air gap that allows the movement of the ambient air and an external layer made of a prefabricated concrete slab. The experimental results of the ventilated roof component during the winter period are presented and its thermal performance is analysed. The effect of key construction parameters like the height of the air gap and the use of a radiant barrier in the air gap is also investigated. Analysis of the results showed that the performance of a ventilated roof component is comparable to a conventional structure during winter. The ventilated component is shown to be in compliance with Greek regulatory requirements in terms of U-value. (c) 2005 Elsevier Ltd. All rights reserved.