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Many contemporary architects are seeking to achieve a closer relationship with the environment. As a result, sustainability criteria and natural processes are starting to be taken into account in the design and construction of buildings.

Gabriel Pérez, a graduate in agricultural engineering from the University of Lleida, has completed a doctoral thesis that reflects this emerging trend. His study examines the use of green façade systems as a means of achieving passive energy savings. The research was carried out in collaboration with the UPC’s Department of Architectural Technology I and GREA Concurrent Innovation, a research group at the University of Lleida (UdL).

Vegetation and architecture have long been combined, but only in recent years have plants ceased to play a purely ornamental role to become one more element of architectural design, with specific economic and ecological functions such as reducing energy consumption. But the use of plants still raises many questions. According to Pérez, “vegetation is often viewed as a component that increases the initial investment and requires maintenance. There’s also a concern that plants may change over time – in terms of their form, weight, or capacities – and end up damaging buildings, even though this needn’t be the case.”

With these issues in mind, Pérez classifies vertical greening systems for buildings in order to highlight key differences and assess each system’s advantages and drawbacks. The first major distinction he draws is between green façades and living walls. Green façades are based on light metal structures (mesh, cable systems, or metal trellises), which are separated from the wall and serve as a support for climbing plants that cover the façade.

Living walls, in contrast, are green walls covered in plants. “Though they have greater visual appeal, they provide no environmental benefit, consume more, and need constant care,” says Pérez. They also cost much more and require support systems that are more complicated to put in place.

In view of these factors, Pérez thinks green façades, particularly double-skin façades, are the most suitable and sustainable alternative for vertical greening of building surfaces. The purpose of this type of system is “to create a green curtain, separated from the façade wall, that intercepts solar radiation and protects the building,” says Pérez. This kind of system “is simpler and easier to maintain and remove” than a green wall.

Green façades have the greatest potential as a passive energy-saving system for buildings because of the shadow effect they produce when they intercept solar radiation.
Pérez took into account that when plants transpire they consume energy and cause evaporative cooling in the adjacent space. This phenomenon creates a microclimate in the space between the green façade and the wall of the building, which acts as a thermal insulation layer.