A Hot Box–Cold Box Investigation of the Corrosion Behavior of Highly Insulated Zinc Roofing Systems

This paper investigates the effect of roofing systems on the humidityinduced corrosion of zinc sheeting in highly insulated zinc roofs. Ten types of roofing systems (U< 0.25 W/(m2K)) were tested in a hot box–cold box apparatus. The measurements and investigations include the relative humidity under the zinc sheeting, the corrosion type, the corrosion product, and the corrosion rate. The influence of a well performing air-vapor retarder below the insulation on the underside corrosion of zinc sheeting is slight for zinc roofs with a good cavity ventilation, but significant if the ventilation is poor. For nonventilated zinc roofs, installing a perfect air-vapor retarder under the insulation only is not sufficient to control the sheeting underside corrosion. Further introducing a dry capillary and sorption active material between the sheeting and the insulation greatly reduces that corrosion.