The air space consists of a hollow “diaphragm” which lies between the load bearing wall structure and cladding, in direct communication with the exterior - as previously men- tioned - from the foot to the top of the building. The thickness of the space is generally about 3-5 cm, although it can increase with the installation of piping and cables. To obtain effective ventilation, it is fundamental that the space maintains a constant thickness from base to top and that it has a regular and continu- ous contour. Particularly important is that it does not have elements which interrupt horizontal continuity and thus create local convective movement in contrast with the principle upward movement of air. The fundamental role of this air recycling cavity is that of enhancing thermal comfort, however, sound- proofing also plays an important part. In summer, the upward move- ment of air reduces the entry of radiant energy inside the building. In winter, air movement together with the cavity’s damping function, reduce the effect of internal-external heat dispersion. Furthermore, in winter the upward movement of air favours the evacuation of water vapour from both inside and outside the building, condensation on surfaces (or within the various layers of wall package).
We have highlighted the need for the air space to be in direct communica- tion (all the way up) with the outside environment. It is also important to apply protective grills at the bottom and top (to prevent small animals from entering), and comple- mentary architectural elements (cornices, flashing, etc.) to help prevent water from entering the air space, which would greatly com- promise its specific function. If all these conditions are respected, the presence of the cavity brings about indisputable advantages like the evaporation of water deposited in the masonry during construction, the con- stant elimination of water vapour from inside during winter, and the cooling down of the building’s outer skin dur- ing summer due to the upward move- ment of air which develops within (and also due to the outer cladding screening solar radiation). Lastly, the shaft of ventilated air helps to make the façade airtight thanks to the notable reduction in the differ- ence of pressure between indoors and outdoors, owing to wind action.