The lookout

Green roofs are used for improving urban environmental quality through reduction of storm water runoff, reduction of heating and cooling costs and of urban heat island impact. They’re still rare in Buenos Aires, especially for public or institutional buildings. However, there are few built projects in the city which can be considered successful examples of the implementation of this urban component.

The roof of the Di Tella University’s main building, located in a residential area of the city of Buenos Aires, is a particular example of green roofs. Extending for 1,600m2 and recently built at the rooftop of an existing five-story building, the new recreational area is only partly implemented as a technical green roof (700m2 meet the general technical conditions of a green roof and 900m2 offer diverse open spaces with no growing medium or plant cover). Here, the key objective was to provide more available open public space for the students and the university’s staff with the bonus of a breathtaking 360 degree view of the city.

Opened in 2013 as a new campus, the site didn’t really offer large green spaces or open gathering areas because its central space is occupied with parking lots. While in the process of changing this situation and with the urgent need of green areas, some professors of the architecture and landscape architecture’s university lists suggested to use the rooftop instead until new solutions would be given to redesign the parking (a competition is in progress with this goal).

The building was originally built in the early 1940s’ to house the installations of OSN (the national water system department) and it was renovated after a 50-year period of stagnation. Ceded by the national government to the municipal one in 1996, the site and the building were the object of renovation after the original uses were turned into educational and cultural. In 1999 it was bought by the university. A first master plan was designed by renowned Argentine architect Clorindo Testa and, based on this layout, a new and final project was delivered by RDR arquitectos in 2011 when the renovation works were already started. The completion and opening of the campus was in 2013. Two years later, the architecture office partnered with landscape architect Cora Burgin to create the proposal for the roof.

Both Burgin and the principals of RDR are professors at Di Tella University listed in the architecture department.

The project for the roof is related to the construction of new master classrooms, administration offices and a restaurant in the fifth floor, which in the past was the rooftop, only used as a machine room. This translated into the fact that the existing drainage system would be “moved up” one floor or at least one of the designer’s main concerns was that of preserving the existing system as much as possible. With this and the structure’s load limits set as priorities, the layout was a combination of engineering thinking and the desire for an urban oasis for students.

The area, which is a rectangle of 90 x 25 metres, was divided into spaces that respond to various possible uses such as relaxing areas, communal spaces and an open-air amphitheatre.

The planting plan is related to this differentiation; the nonaccessible areas are covered with a combination of sedum species which have minimum maintenance requirements and provide colours and textures. Some patches were to be covered with lawn for people to be able to sit and lay down. These lawn areas coincide with (and are built on) the slopes of the gable roof which was designed for the master classrooms in the new architectural project. The heights and shapes of this roof were given by the city zoning and the original proposal of architect Clorindo Testa. However, anticipating the need of walking spaces, the architects reduced the area of the gable roof by leaving available areas at three sides of the rooftop and resulting in a U-shaped esplanade.

When extending along the full extension of the larger side of the roof this esplanade turns into a generous three metre-wide promenade. Finished with concrete tiles and edged by a tall transparent curtain-wall, this linear piece becomes the mainconnector between the different spots. A continuous balcony opening onto the city, the large old trees planted in the nearby neighbourhoods, the River Plate Stadium (the largest in Buenos Aires) and looking northeast, the splendid river which actually gave name to it.

At the eastern side of the roof, where in the future will be placed an open-air dining area, a row of trees bloom in the summer and fill the air with perfume. Planted on a deep layer of earth of 20cm these Bahuinias (Candida’ variegated orchid-tree) offer a natural look to the roof. The location of the trees at this corner of the rooftop responds to the need of concentrating the higher loads at the edges of the slab and making them lighter at the centre. The planters were finished in a way that a row of Bahuinias seem to be coming out from a wooden prism, which can also be used as a bench. This nine-metre long piece covers and unifies the individual planters and, from an aesthetical perspective, adds a crafty image to the quite urban scene.

The placement of wooden benches all throughout the site is something that creates visual harmony and at the same time offers a variety of situations. The different shapes and lengths of the benches respond to different uses and positions. Two benches with backs, five metres long are placed close to some garden-like spots. Here the landscape architect decided to plant different kinds of sedum and herbaceous which provide colour and blooming year-round.

But it is in the open-air amphitheatre which creates the perfect ambience to rest and watch, where benches take over as an attractive set of outdoor furniture. Placed in three rows of seven 4.50 metre-long benches, this arrangement is a great spot to enjoy views and the breeze.

“We wanted students to have the option to sit around and appreciate the vistas, but also had to make sure that this would happen at the less windy part of the roof” explains Cora Burgin. For this reason, the design saves the northern side, which is the most exposed to the river winds for the machine room. Some of these installations existed and to be able to group the whole equipment at one single area, some more were moved here. In a poetic gesture and challenging any winds, the designers built a lookout - made with the same metallic structure used for the stairs that go down to the classrooms, this small belvedere reaches the highest level of the building, on top of the machines area, from where one can see even further the crowns of the urban woods and the river.

The lawn patches built over the gable roof have a deeper layer of earth than the rows of trees. The continuity of the green planes, which coincide with the two roof panels, allows visitors to feel immersed in a landscape of gardens and sky. Bruno Emmer, one of the lead designers of RDR architects, recalls a romantic drawing made by Amancio Williams, another renowned Argentine architect from the 1940s’ - a simple sketch representing a garden, the horizon, and a sunny sky. For Williams, this scenewould be the most desirable for an urban view. “In some way”, says Emmer, “This is what we wanted to achieve for this place: a view of plain green and blue.”

At the sides of every one of the lawn patches a series of stepping stones, made of geometrical concrete pieces, lead up to the highest point of the roof (except for the lookout). Framed by a thick border of ornamental grasses and low shrubs, these white pieces contrast with the relaxing green of this place.

As for the functional aspect of the project, the drainage system was the most important issue to solve. As aforementioned, the team decided to make use of the existing one, by connecting the new roof drains and new segments of downpipes to the standing drainage structure, already connected to the municipal system. In order to make the new construction and maintenance easier and more efficient, the landscape architects decided to have a“floating floor” underneath which are located the drains. The roof’s percent slopes are thougth out for the stormwater runoff to be conducted to these spots, placed along thefull extension of the esplanade. In order to assure regular checking tasks, some of the concrete tiles which make this floor are removable.

At those spaces where the planted areas are flat, a low retaining wall (whose height is the same as that of the floating floor) is perforated for the exceeding water to go through and reach the hidden drains. On the other hand, the lawn patches slope down toward a linear gutter which edges the full length of the patch and catches the runoff to be conducted to the drains.

Completing the project, the roof presents four sunken small backyards which can be accessed from the master classrooms and offices in the fifth floor. In the past these spaces used to be skylights. By keeping them at the same location and building the courtyards around them, the architects made a clear decision of preserving the original structure as much as possible and the gaining of natural light in the classrooms as a top priority. The vent pipes which come out at the roof level were covered with plate metal and appear as vertical sculptural objects. More importantly, they stand there to remind anyone of what a roof actually is.