The condensation risk of the top envelope of low sloped roofs with air ventilated cavity has an important factor in the designing phase of these building structures. The significance of sky radiation plays an important role in the radiation heat exchange specifically during night-time (winter and transient periods) with regard to heat loss and condensation risk at the top roof envelopes. Basically, the design principles and current development of standard requirements have limited and simplified implementation of this phenomenon. The importance of a relevant design of these types of roofs are being addressed as highly important issue in the building application to predict its reliable hygrothermal performance. In this context, the paper presents results of numerical study, where thy sky radiation effect is carefully taken into account. It provides a numerical analysis on the minimalization of the condensation risk at the top envelope of low sloped roofs with naturally ventilated air cavity. Based on this, a performance prediction of thermal properties degree and its influence due to condensation risk occurrence is obtained, where real climate data for location of Brno, Czechia, is specifically employed. The results demonstrate hour's quantity of condensation risk occurrence in terms of thermal resistance correlation for data obtained through the whole climatic year.

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