Manti permeabili per tetti traspiranti

That the ventilation in the roof effectively fulfils the cooling function of a building is a well-established concept. However the common opinion associates the working of a ventilated roof only related to the “chimney effect”, neglecting the fact that in discontinuous coverings (such as clay tiles coverings), most of the heat is dispersed by ventilation through the joints of the tiles, with beneficial effects. This paper reports the results of several experimental activities in this regard. We monitored the summer thermal performance of full-scale roofs, built according to the current requirements of thermal transmittance, with different types of coverings (clay tiles, copper) and height of air gap (3 cm and 6 cm). Results show that clay tiles roofs are more effective than copper roofs in cooling the internal environment, and that in roofs with low thermal transmittance, it is of little convenience to invest in elevated air gaps. A tracking smoke test of the air movement into the roofs showed that most of the air entering into the gaps of clay tiles roofs then escapes through the joints of the tiles. Laboratory tests allowed to quantify this airflow and to correlate it to the amount of heat removed by ventilation in a clay tile roof