Design and calculation of the internal roof drain system structure in terms of thermal protection and moisture condensation

Abstract

A field survey of roof structures of several administrative buildings in the temperate climatic zone showed the presence of condensate in the zone of the internal drain. The fact of overmoistening of the roof structure raises doubts about the operability of the roof aerators installed on these coatings, designed to remove condensate from the roof layers. The inefficiency of using roof aerators can be explained by the process of condensed moisture freezing in the structure during the cold season thus cannot be removed by aeration. Two types of structures of the internal roof drain system used in construction from the point of view of condensate formation are revealed. The difference between the types is the degree of water vapor permeability of the junction layer between the pipe and the coating plate. An impermeable solution can be made by mounting a steel flange at the junction of the pipe and the coating plate. The vapor-permeable solution is made in the form of a simple sealing of the gap with polyurethane foam or other permeable materials. A calculated analysis of the temperature fields and the humidity conditions of the two types of internal roof drain structures showed that the use of polyurethane foam or its analogs in the gap is not enough to protect the roof structure from condensation. This solution leads to condensation inside the structure at positive outside temperatures (less than 2 °C). The design with steel flange at the junction of the pipe and the coating plate is free from these drawbacks and can be used at lower outdoor temperatures.