Ventilation in Traditional Coverings an Analysis of The Hygrometric and Thermal Behavior

The use of ventilation technologies for roofs has become widespread in several countries in order to reduce the energy loads on air-conditioning systems. In a number of Southern European countries ventilation systems are characterised - from a technological point of view - by the fact that they are made of tiles lifted by means of wooden elements or insulating sandwiches. This brings about the presence of a ventilation chamber whose thickness varies from 2 to 6/7 cm. Nevertheless such values contrast with the data derived from the analytical models based on the classic ventilation theory and make it necessary to have higher ventilation chambers. This article is based on the results from the tests carried out on 5 types of ventilated coverings on an experimental building for a whole year. It shows that the discrepancy can be ascribed to the high air permeability characteristic of the covering mantle. The tests make it possible to prove the reduced applicability of the classic ventilation theory [Hens,1999] and provide data on the hygrometric and thermal behaviour of ventilated coverings for a whole year. In particular, the most significant results are as follows: - during the winter ventilation determines considerable increases (25%) in the thermal flows transmitted towards the outside. The results are much worse than for comparable non-ventilated coverings; - during the summer ventilation determines a remarkable decrease in incoming thermal flows towards the environment. The decrease is not directly related to the ventilation section, but seems to be influenced by the permeability in the mantle; - again during the summer the simple increase in the insulating layer in the non-ventilated covering results in an improvement comparable to that of ventilated coverings; - from the hygrometric point of view ventilation acts as a humidity dissipator only for short periods during the day and only for some periods of the year.