The reduction of heat losses in building constructions gains more and more significance as further energy savings will be demanded in the future. Heat loss occurs in inverted roofs due to the drainage of warm rainwater beneath the thermal insulation boards. This rainwater cooling effect has to be considered as an additional heat loss ?U, which must be added to the designed U-factor for the roof construction. An improved inverted roof construction with reduced heat losses has been developed. It was the idea to install a second drainage layer above the insulation boards, which has to be water resistant and vapor permeable at the same time. The water-repellent layer, consisting of loose-laid overlapping sheets of a special nonwoven fleece MK, replaces the usual separating layer laid between the insulation and ballast. The water-repellent layer prevents most of the rainwater from reaching the waterproofing membrane beneath the XPS boards, thereby almost completely eliminating the rainwater cooling effect. The scientific investigations, which led to official regulations in Germany and other European countries, are presented.

Authors: Holger Merkel, Ph.D.

Citation: Thermal Performance of the Exterior Envelopes of Buildings VIII

Keywords: December, Florida, 2001