El Fil Verd has completed a sustainable, cork-clad passive house on the edge of the Garraf Forest near Barcelona.


Milena Villalba

The House in the Forest occupies a steeply sloping, north-facing plot on the edge of Spain’s Garraf Natural Park, close to Barcelona. The brief to architect El Fil Verd was for a low-energy, cost-effective, detached dwelling that would form a close connection with its site.

Conceived as a passive building, the three-storey structure is partially buried to complement the site topography and take advantage of ground’s insulating properties. The plan comprises two wings, which open-up to the north. The street-facing facades are devoid of openings for reasons of privacy. Located on the ground floor are the main living spaces and a bedroom. A second bedroom, together with a large terrace, solarium and garden occupy the first floor.


Aerated concrete blocks were chosen for the external walls for their lightweight and highly insulating properties. The facades are clad with thermo-treated natural cork panels, which provide further insulation and help the building to blend in with the surrounding landscape. Pine softwood treated with natural stains is used for the exterior joinery. Inside, lime and silicate paints are used throughout, while the exposed floor slabs are finished with quartz crystals.

Ground and first-floor plans; section

Environmental design is central to the project, with the building oriented north-south to take advantage of solar radiation in winter and natural ventilation in the summer. The partially glazed south-facing façade is conceived as a solar heater. In the winter, solar radiation penetrates the interior and is transformed into heat, increasing the temperature.


The Trombe-Mitchell walls function as ‘solar chimneys’ on hot days, extracting warm air from inside and replacing it with fresh air from the outside. In colder months they function as hot chambers, trapping heat and transferring it back to the interior by convection and radiation.


Deciduous trees planted in front of the south façade provide protection from intense summer solar radiation. A pond located close to the building helps to cool the summer air. The project also makes use of roof-mounted photovoltaic panels and grey and rainwater recycling.

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