Location: Santiago, Chile
Architects: Alejandro Aravena
Area:  5000 m²
Year of completion: 2005

Siamese Towers by Alejandro Aravena - Sheet1
Siamese tower_©https://images.adsttc.com/media/images/500e/c4df/28ba/0d0c/c700/03a1/slideshow/stringio.jpg?1414325767

Alejandro Aravena designed the Siamese tower in Santiago, giving an imaginative yet straightforward design approach to the client’s requirements. A tower situated in the south of Santiago would have to be futuristic and suited for the hot environment conditions of the region as well as reflect the digital era as a house of computers. A high-rise building is designed by the architect, which despite its outside appearance of being delicate and unconventional, is iconic, spacious, and sturdy. Even though little funding was available, the architect managed to design this building so that each building material and architectural feature had a purpose and added to the building’s overall character.

Siamese Towers by Alejandro Aravena - Sheet2
Section through the tower_©https://images.adsttc.com/media/images/500e/c507/28ba/0d0c/c700/03ab/slideshow/stringio.jpg?1414325789

One of the client’s main criteria was that the façade be made of glass, which had more drawbacks than benefits when used as an outside covering for the structure. The quantity of thermal gain from the environment would grow, not to mention the difficulty of utilising a computer in direct light, and employing engineered glass to regulate light and heat gain would raise the cost of the structure. As a result, the architect employed facades with the inner façade composed of asbestos cement supported by the grid of reinforced concrete grid, which helped to minimise light reflection and heat gain. While the outside curtain wall was composed of tempered glass, it was supported by a steel framework perimeter that was anchored to the reinforced concrete building’s interior structure. The 80cm gap between the two layers allows air to enter between the two facades and exit via the top aperture, generating a convection effect that prevents heat generated behind the glass façade from reaching the asbestos cement layer. This design feature reduced the cost of a single energy-efficient glass wall by approximately 30%.

Siamese Towers by Alejandro Aravena - Sheet3
Day – Night views of the tower_©https://images.adsttc.com/media/images/500e/c4ed/28ba/0d0c/c700/03a4/slideshow/stringio.jpg?1414325777 (Left)_©https://images.adsttc.com/media/images/500e/c4e9/28ba/0d0c/c700/03a3/slideshow/stringio.jpg?1414325779 (Right)

Another requirement for the structure was 5000 sqm of floor area on each level, which necessitated a height that made the structure appear chubby and monotonous. The plan was to divide the tower in half from the seventh storey, hence the tower’s symbolic name. This resulted in an adequate floor plate as well as the uniqueness of the structure. To lend character to the tower, one section was constructed of silver aluminium and the other was built of black aluminium; the difference in hues helps the structure stand out, especially at night when the lights are turned on.

Siamese Towers by Alejandro Aravena - Sheet4
Building within a building_©https://images.adsttc.com/media/images/500e/c4d8/28ba/0d0c/c700/039f/slideshow/stringio.jpg?1414325771
Siamese Towers by Alejandro Aravena - Sheet5
Architects initial sketches_©https://4.bp.blogspot.com/-lFeN_WjqiOw/VPJaTnvRvRI/AAAAAAAAKt8/nKO3Dhg1J0M/s1600/image10.jpg

The visually deceptive design leads the observer to imagine that the building is modelled from several angles. Even though the beams and columns of the interior facade structures are parallel and perpendicular to the ground, the glass frame on the exterior is angled in various directions. The building’s glass frame maximizes natural lighting and forms an angled exterior façade layer. The juxtaposition of the outside mullions and the angled articulation of the fibre-cement panels provide the building with a more dynamic aspect through the interaction of diverse material modules, while also emphasizing the slanted structure’s deception. The idea of a building inside a building is admirable and exquisitely executed, from the conceptual phases as shown in Alejandro’s preliminary sketches to the completed construction that is hardly viewed in a straight line.

Siamese Towers by Alejandro Aravena - Sheet6
Ground floor entrance and auxiliary spaces_©https://images.adsttc.com/media/images/500e/c500/28ba/0d0c/c700/03a9/slideshow/stringio.jpg?1414325773 (Top left) _©https://images.adsttc.com/media/images/500e/c4f6/28ba/0d0c/c700/03a6/slideshow/stringio.jpg?1414325782 (Top right) _©https://images.adsttc.com/media/images/500e/c4f9/28ba/0d0c/c700/03a7/slideshow/stringio.jpg?1414325784 (Bottom)

The building comprises nine floors, two basements, and two auxiliary structures on the first and second levels. The basement is two stories high and continues up the deck of the adjacent structures. The top is accessible to the general public through ramps. It is made of inclined planes of indigenous wood, influenced by the requirement for an economically sloping roof for the auditorium located below ground. The ground produces a continuous surface that allows for a ‘ground level’ entrance to the two main levels as well as several meeting places close to the structure, resulting in a third Siamese twin.

Siamese Towers by Alejandro Aravena - Sheet7
open communal spaces_©https://images.adsttc.com/media/images/500e/c4e5/28ba/0d0c/c700/03a2/slideshow/stringio.jpg?1414325769
interior spaces_©https://images.adsttc.com/media/images/500e/c4f1/28ba/0d0c/c700/03a5/slideshow/stringio.jpg?1414325780

The communal and informal rooms open onto or are positioned inside the perimeter’s ample natural light, whilst the office and classroom areas, which are located in the centre of the building, are designed with light management in mind. To minimise light bouncing off the displays, the rooms in the building where computer studies are performed are kept semi-dark. The tower’s base was buried, which reduced the need for openings. The nine-pointed region created between the two buildings is expected to be a key public mobility and structural centre.

Large perforations at the base and tops of the glass envelope promote convection currents to air the region, absorbing the unavoidable heat gain caused by the strong Chilean sun. Understanding the value of both in-person and online interaction,  the inner wall reduces light for the latter, while the air gap and adjustable panels help encourage thermal comfort without the need for expensive air conditioning. Siamese Towers is an example of a completed challenging architectural task. It is the result of current technology and mathematical calculations coming together to create a distinct and eye-catching tower.


  1. https://en.wikiarquitectura.com/building/siamese-towers/
  2. https://www.archdaily.com/1277/siamese-towers-alejandro-aravena
  3. https://www.building.am/buildings-index/siamese-towers-santiago-chile/
  4. https://archidose.blogspot.com/2009/08/the-siamese-towers.html
  5. https://www.elementalchile.cl/wp-content/uploads/071005_PRAXIS_SIA_60-67_LOW.pdf

Srushti is an aspiring architect who believes that every structure and place contains an underlying story that can be experienced by everyone. She is a modest observer who uses her keen understanding to comprehend the world. This exposition is constantly pushing her in order for her to absorb and learn, unlearn and relearn.