Zinc roofs: an evaluation based on test house measurements

In cool and cold climates, interstitial condensation in flat and low-sloped roofs is eliminated by the application of two separate measures: (1) avoiding water vapor from entering the roof from inside; (2) facilitating the evacuation of water vapor that entered by providing a ventilated air space below the roof cover. For decades, manufacturers of metallic sheeting defended the second option as the only one acceptable for metallic roofs. Concerns about costs, however, intensified the interest in new solutions such as compact roofs. The article describes a long-term test building research on compact and ventilated metallic roofs. The outcome after 4 years of testing is both logic and remarkable. Air exfiltration, if any, dominates the moisture response of the compact roofs and increases the risk of moisture attack in ventilated roofs. Also no clear correlation was found between the presence of ventilation, the severity of interstitial condensation and the degree of underside corrosion of the zinc sheeting