Tiled roofs air permeability: experimental and numerical investigation

Abstract

The construction sector accounts for more than one-third of the global energy consumption. Ventilated roofs and facades are among the adopted strategies to improve the efficiency of the building envelope: air flowing in cavities under the cladding layer, in fact, is particularly effective in hot summers for the reduction of the incoming heat flow due to solar radiation. Regarding roofs, satisfying results were obtained through the realization of a 5-10 cm air gap under the covering layer which allows better thermal performances of the roof and a reduction of the energy consumption for air conditioning. Although most of products and techniques applied are based on the assumption that air enters only from the eaves line and exits at the ridge one, it is demonstrated that in case of discontinuous mantles, a great contribution derives from air entering from the overlaps. As a matter of fact, air entering from the eaves line is strictly dependent on the wind direction and benefits are evident only when the wind is perpendicular. In all the other cases, buoyancy forces due to air heating under the mantle cannot provide such a consistent contribution. Tiles overlaps’ air permeability allows the wind to enter from multiple directions with consequent greater ventilation of the substrate. Experimental research regarding the performances of pitched tiled roofs was conducted at the TekneHub laboratory of the University of Ferrara and the results are here presented. The tests carried out aimed at investigating the behaviour of different configurations of tiled roofs both from a thermal and an energetic point of view. Three configurations were compared: one was a completely sealed roof (sealed), one had sealed eaves and ridge lines but unsealed tiles overlaps (laid) and the last one was a ventilated roof (vented). The comparison between the sealed and the ventilated roof confirmed the improvement of the performances when in presence of an air cavity. The ventilated roof was then compared to the laid roof to assess the actual contribution of the air permeability of the tiles, and results clearly showed a great contribution, even in case of low wind.