A sloped-roof structure, having only one ventilation airspace, is studied in this paper. In this sealed cold-roof system, the underlay foil forms a nonventilated airspace above the thermal insulation, which improves the thermal performance of the roof. The internal moisture loads can be transported by diffusion through the highly vapor-permeable underlay to the ventilation cavity. The sealed underlay system works also as an additional resistance against air leakages. The thermal and moisture performance of the sealed and conventional roofs were studied in field experiments done in a test building in southern Finland. Different roof sections have been studied for three heating seasons. The experiments show that the sealed roofs have as good a moisture performance as conventional roofs. With similar air leakage paths and pressure differences, the sealed underlay system could decrease the leakage airflow rate by 15% and the total heat losses through the ceiling by 23% when compared to a conventional roof.

Authors: Tuomo T. Ojanen

Citation: Thermal Performance of the Exterior Envelopes of Buildings VIII

Keywords: December, Florida, 2001