ABSTRACT
In metal roofs, interstitial condensation is one of the main malfunctions. Metal sheeting in fact has a thermal resistance close to zero and cannot buffer moisture. As a consequence, condensation typically results in water droplet accumulation and dripping. Since decades, the industry proposes two rules of practice to prevent the problem: a vapor barrier below and a ventilated air space above the thermal insulation. A performance based analysis shows that both measures may function most inadequately if acceptable air-tightness is not guaranteed and condensation by clear sky radiant cooling is not neutralized. The research advances some new priorities in metal roof design: air-tightness, non-vented compact solutions and the use of a sorption active support below the sheeting.
