Ventilated glass facades

The glass that covers the entire facade plays a role in continuous wall in which the openings can be exposed, highlighted, or hidden in the homogeneous surface. The glass surfaces can therefore also correspond to blind walls of the building and the function of the wall is to protect the internal layers and of an aesthetic nature. In the past, glass walls corresponded to a strong heat dispersion or an accumulation of heat due to the greenhouse effect, now there is the possibility of creating facades with ventilated systems that have the advantage of responding to the requirements of insulation, lightness and architectural value.

Benefits

• Aesthetic and architectural characteristics of the facades.
• Realization of the coating with dry methodology, which allows, over time, to guarantee the replacement of elements in a timely manner, without intervening on the entire wall.
• Energy saving, which determines excellent performance and the elimination of thermal bridges.
• Excellent response to rain and atmospheric agents, with elimination of condensation.
• Acoustic insulation determined by the stratigraphy of the ventilated wall.

The panels and their thermal insulation are fixed to the walls through substructures anchored to the perimeter surfaces of the building and in the cavity the air circulation generates the chimney effect which allows for improved energy performance.
Like light duvets that can protect us from the cold, ventilated walls cover the entire building, eliminate thermal bridges and offer an excellent response to the harmful effects of humidity.

Composition of the ventilated wall

• External insulation on the perimeter wall of the building.
• Ventilated air chamber.
• Substructure supporting the external cladding, usually made with a network of metal/wood supports or with point supports
• External glass facing.

Among the insulating materials, mineral ones are preferable and the anchoring elements must be specifically designed to contain heat loss. 

Characteristics of external insulation

• Ensured flatness of the surface, usually achieved by using rigid insulating panels.
• Breathability, to avoid condensation, even with the insertion of vapour barriers.
• Anti-mold and durability resistance features.
• Fire resistance, to prevent the chimney effect from facilitating the spread of fire to the entire surface of the building.
• Resistance to UV rays and high temperatures.

Ventilation gap
The ventilation layer, present between the insulating layer and the external cladding, uses the chimney effect that is generated by the temperature differences and natural convective motions by virtue of which the hot air, which has a lower density, tends to go upwards, while the cold air goes downwards.
The glass walls are partially able to reflect the heat to the outside and the residual heat is dissipated by the air chamber which generates a convective motion of the air, the so-called “chimney effect”.
This is caused by the difference in air temperature in the cavity and is regulated by the openings at the base and top; the operation is activated by the heating which, through the external wall, is transferred to the cavity generating the upward motion, allowing, thanks to the ventilation of the wall, a decrease in temperature. The cavity also serves the function of energy containment during the winter season and the external facing protects the internal layer, maintaining the internal temperature of the building in balance, leaving it dry and free of thermal bridges.
The gap, usually between 3-5 and 7 cm, it must be sized both to avoid excessive convective motion and channels that are too narrow and prevent proper ventilation.

Supporting substructure and related anchors
The substructure is usually made with a network of metal or wooden supports, of the upright, crosspiece, upright and crosspiece type, or with point supports. The substructure and its anchoring hooks must be sized and evaluated in relation to the weight to be supported and the limit conditions, determined by the wind and seismic agents.
The technology with which the fixings are made can be visible or hidden; it is a dry system with special stainless steel hooks.
The UNI 11018:2003 standard (Cladding and anchoring systems for mechanically assembled ventilated facades) dictates the characteristics of the systems that must be equipped with adjustment elements to ensure the flatness of the installation, usually thanks to elements in aluminum or stainless steel or zinc-titanium. Among the types of fixing, hyperstatic, diffused, with frame uprights are preferred to isostatic, point-type ones (clamps, brackets)

External coating
Among the cladding systems, glass sheets can provide extraordinary aesthetic effects by providing lightness and transparency because they allow for the creation of surfaces in which the opening elements of windows and French windows are inserted into the continuous facade. These systems can be created using prefabricated structures with exposed or concealed, completely invisible, aluminium profiles. The sheets can alternate glass surfaces and surfaces of other materials or glass surfaces with different colours and surface treatments, and carry transparent, semi-transparent or mirror-type glass elements. Thanks to the new characteristics of the materials, it is possible to obtain stratified glass capable of filtering solar radiation.
It is possible to obtain effects of total coplanarity that completely hide the substructure frame from view and the glass can be particularly efficient both from the point of view of thermal insulation and from that of acoustic insulation. These walls maintain the characteristics of protection from atmospheric agents, they favor the breathability of the buildings, thanks to the cavity that preserves the internal structure from humidity.
This technology is based on the modularity of the elements used and, in the event of damage to the external facing, each individual slab can be replaced.
Among the most innovative systems, they also offer the possibility of creating facades that exploit solar energy to generate electricity, through photovoltaic technology.
The windows can be solar control and low-emissivity glass, which allow for better environmental comfort and significant energy savings, with the enhancement determined by the large glass surfaces and the benefit of passive solar gain.
Laminated glass reduces the possibility of accidental breakage, protecting people and property. There are also special self-cleaning glass, used in the surface layers of laminated elements, to contain management costs and characteristics over time.

Performances

Behavior in water
Glass walls preserve and protect from the action of water by insulating the underlying walls, also preserving the underlying insulation. Any filtered water is disposed of through the cavity. The formation of condensation in the interior is limited and eliminated thanks to the breathability of the insulation, the thermal action determined by the combined effect of the insulation and the ventilation chamber.

Fire behaviour
The cavity, the insulation, the supporting substructure and the relative anchoring hooks, the casing, must guarantee both individually and as a whole good behaviour in the event of fire, complying with the Circ. 5043 of the Ministry of the Interior.

Behavior in the wind
The plates used, in their shape and size, but also the fixing and anchoring systems, must be checked for both compressive and tensile stresses, as well as for fatigue resistance.
For calculation and sizing, always consider the worst climatic conditions, using the greatest possible precautions.

Thermal and acoustic insulation
The external insulation and the ventilated cavity guarantee good thermal comfort in every season. Compliance with the DPCM 5/12/1997 is obtained by the reflection, absorption and acoustic transmission, thanks to the stratigraphy of the ventilated facade. To determine the thermal transmittance value of the vertical walls, the checks should take into account the seasonal variations, considering the reflections determined by solar radiation and the effect of ventilation and the insulating layer, evaluating the possibility of modulating the air intake and exhaust grilles.