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 humidity-induced corrosion of zinc sheeting in highly insulated zinc roofs. Ten types of roofing systems (V <0.25 W/(m2 K)) 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.