Bunyesc Arquitectes has transformed a house in northeast Spain into a low-energy building by adding a new polycarbonate plastic facade.
The Lleida-based architecture studio aimed to improve living conditions in the old house, which is located in the town of Pessonada, by improving the building's thermal efficiency.

To achieve this, the team installed eight-layer polycarbonate panels to the outside of the building's south-facing stone wall. The aim was to significantly increase the level of insulation and also allow the building to passively store energy from the sun.
"This facade modification makes it possible to reach a pleasant indoor climate, by capturing the solar heat/energy and gradually transferring it indoors," explained architect Josep Bunyesc.
The polycarbonate layer acts as an external layer of insulation, but also gives the exterior wall a much greater thermal mass, allowing it to slowly release heat into the building over long periods of time.
"Due to the state of disrepair of the south facade it was not possible to significantly enlarge the size of the windows. Therefore, it was difficult to capture the solar energy and increase the heat gains," Bunyesc told Dezeen.
"But this change transformed the stone wall into a large solar thermal collector."

In the winter, the angle of the sun means that a great amount of solar radiation is absorbed by the polycarbonate. Contrastingly, most radiation is reflected from its su...