Performances of highly insulated compact zinc roofs under a humid-moderate climate - Part I: hygrothermal behavior

Four flat compact zinc roofs with a U-value less than 0.25 W/(m² K) were investigated under a humid-moderate climate. Two roofs had a heavyweight deck, the other two a lightweight deck. The heavyweight roofs exhibited a satisfactory thermal behavior. The small amount of moisture accumulation in the insulation did not result in a measurable degradation of thermal quality of the zinc roofs. It was found that the moisture situation at the sheeting underside was much better in the heavyweight roofs than in the lightweight roofs. However, in the heavyweight roof with a perfect air-vapor retarder, a large number of wetting/drying cycles at the sheeting underside were measured in winter. Strong sheeting undercooling was also observed in the four roofs during the test period. The results show that it is possible to build low U-value compact zinc roofs with a perfect thermal performance.