Spanish architecture firm OHLAB has recently completed Paseo de Mallorca 15, a residential complex on a V-shaped corner site in its native Palma, Mallorca. The project is defined by a unique textured facade of sliding panels with a lattice of natural wooden slats. This adaptable brise soleil serves as a secondary outer layer, effectively filtering the intense Mediterranean sunlight to lessen solar heat gain on the building while preserving outward views from the apartments onto the cityscape. The design, according to the architects, draws inspiration from the pergolas and shutters peppered about the Mediterranean island.
Mallorca is one of the five inhabited Balearic islands located off Spain’s southeastern coast. Palma, a city with roots as a Roman port, is located within a large bay on Mallorca’s southern coast. OHLAB’s new residential project is situated along the Riera of Paseo Mallorca, a recently-developed and lushly-vegetated pedestrian walk that winds through the western side of the city to connect a large park with a museum and port to the south.
The building is designed as an extension of the Paseo. One enters the complex from the street into a space marked by a green wall of Spanish cane, typical of Mediterranean riverbeds. This leads to an inner vegetated courtyard that extends over multiple levels and, according to the architect, acts as 'an inner lung of vegetation and trees.' Here, a waterfall extends to the basement level and helps cool the exterior space in the summer through evapotranspiration. Lighting and vegetation reach the basement, which houses a communal pool, gym, and spa. The courtyard serves as a vertical axis through the building, allowing for cross-ventilation in each of the apartments. The building is finished in a simple palette of fine materials that harmonize with the Mediterranean location, including solid doors made of local stone, aged bronze pieces used in the interiors, as well as wood and concrete facades.
Designing a Passive House building for a warm climate
Mallorca’s climate experiences hot summers and mild winters. Paseo de Mallorca 15 was designed in accordance with the strict, yet voluntary, Passive House standards for energy efficiency. These standards serve as a guide for reducing the ecological footprint of construction and aim to create buildings that require minimal energy for heating or cooling. The project was meticulously planned to meet heating and air-conditioning demands of 15 kWh/(m2y), representing an estimated 90 percent reduction in air heating and cooling requirements compared to typical residences of this scale in Mallorca. Passive House standards particularly influence the design of building envelopes, which must be continuously insulated and airtight.
A building with two skins
The building volume is enveloped in two distinct facade types. The first features a sort of double skin with large windows on the inner portion and an outer permeable layer made of wooden slats. This facade encases the daytime areas of the apartments, situated on the sun-drenched east elevation facing the public Paseo. The windows allow residents to enjoy the views, along with the shade provided by the outer moving panels in the summer, which can be slid open to welcome the winter sun. As it is operated by individual apartment owners, this facade serves as an often-changing organic layer. The second facade type consists of a thick and more opaque skin clad in glass reinforced concrete (GRC), located on the bedroom side of the building, facing the quieter side streets to ensure privacy.
A permeable facade for views
The facade of the daytime areas is positioned closest to Paseo Mallorca, offering unobstructed views of the river and surrounding gardens. This facade was designed with large windows externally protected by a wooden lattice. A small balcony between the windows and the lattice allows for the adjustment of the position of the wooden panels and facilitates cleaning and maintenance of the glazing. The wooden panels filter the incident light on the glazing, protecting it from direct solar radiation. Double glazing with a chamber and a solar factor G coefficient was selected for the windows to meet the stringent energy calculations of Passive House.
Seville-based Grupo GUBIA designed, manufactured and installed the wooden envelope of fixed and mobile lattices, a patented envelope system called the GUBIA Facade Sliding System. According to the manufacturer, the exterior wood used in facade is sourced from FSC and PEFC managed forests. The proximity to the sea was a crucial factor in specifying heat-treated Scots pine wood of European origin for the 350 fixed and sliding panels. This species offers excellent outdoor performance, further enhanced by applied heat treatment to minimize contraction and expansion.
The wood utilized in the project is thermally treated wild pine, known as Thermo-D, where the 'D' signifies durability. It's coated with natural waxes in cream form for protection. Each slat is meticulously crafted, rounded at the edges, planed on all sides, and sealed with water-repellent pigmented wax. These treatments not only shield the wood from moisture but also maintain its breathability. This process results in a semi-transparent finish, showcasing the natural grain of the wood. Gray cream was chosen for the lattices, while a richer chocolate hue was selected for the facade linings.
These carved slats, measuring 42x42, 42x68, and 42x90 millimeters, alternate on a matte silver anodized aluminum frame with varying separations, creating a visually diverse array of modules. The wood sections are connected using rods and stainless steel AISI 316 spacers, ensuring both the straightness of the pieces and the spaces between them. To fix the modules in place, a proprietary system of guides and stainless steel bearings has been developed. These are mounted on 15-millimeter-thick CNC-machined aluminum plates, secured to the perimeter of cantilevers using chemical bolts.
Three continuous grooves, covered with boards of the same wood, create an organic and changing veil on the building's exterior, reflecting its inner life. This veil serves as an optimized filter based on solar studies, adapting to various climatic needs while drawing inspiration from traditional Mallorcan pergolas and blinds. The facade lattices, along with cross ventilation and a heat recovery system, play pivotal roles in maximizing the building's energy efficiency.
Behind the wooden lattice are large windows crafted from red pine wood 'sepi', meeting the required Passive House construction standards. This wood is stained dark chocolate for improved maintenance and durability, contrasting with the exterior slat facade. The choice of this material and its finish aims to infuse warmth into the interior, highlighting the natural and noble materials used throughout the project.
The balconies needed to be thermally separated from the interior structure to prevent thermal bridging. This was accomplished using a linear structural connector equipped with built-in thermal insulation, positioned between the perimeter of the slab and the balconies. Known as HIT-HP/SP MVX anchors, these connectors provide support for shear in both directions and negative overturning moments. They are installed in approximately one-meter-long sections, with their placement specified in plan based on the load requirements for each connector.
An opaque concrete facade for privacy
The facade in the bedroom and bathroom areas, considered the most private zones of the homes, features an exterior finish of ribbed GRC panels. These panels include openings to provide lighting and ventilation to the rooms. They are stud-framed with a thickness of ten centimeters and contain interior thermal insulation encapsulated within the GRC.
The installation of the GRC panels occurred after the completion of the structure, with each panel supported by anchors on each floor. Behind the panels, a layer of polyurethane foam with a thickness of five centimeters was added, along with an exterior brick enclosure measuring 11.5 centimeters in thickness.
To ensure air tightness, a vapor-regulating and airtightness membrane was applied to the interior face of the brick enclosure, extending from the lower to upper concrete slab. This membrane helps limit air infiltration into the homes and underwent testing to correct any identified airtightness issues.
Inside the homes, a partition with thermal insulation made of rock wool and double hollow brick with a thickness of seven centimeters was constructed. It is internally finished with a lime mortar coating, allowing for the embedding of installations such as mechanisms and light points.
