Final review: STACKED BALCONIES


A perforated concrete facade with randomly positioned openings wraps the skeleton of the Piraeus Tower. The homogenous texture of openings breaks with the strong verticality of the skeleton and introduces a notion of mass, pronouncing the strong presence of the tower at Piraeus port.

The openings are occupied by three different types of windows:
Type A: A simple window
Type B: A box-type window consisting of a simple window in combination with a exterior glass panel. This window type operates as a natural ventilation device. The hot air in the buffer zone rises and evacuates air from the interior spaces.
Type C: A balcony between a recessed window and exterior glass panels. The balconies create natural ventilation as well, but only if several of them are stacked on top of each other forming a vertical shaft.

Each opening is assigned a window type according to the three main environmental parameters: Noise, sun and wind. The data describing these parameters is translated into image maps. Using the RGB additive color model, all information can be condensed into to a single image.

The window types are assigned as described in the last post:

A script evaluates the parameters for each window position. A lot of noise or wind demands a box-type window that offers more protection than just a simple one. Where the sun intensity gets more important than noise pollution or wind forces, a simple window is preferred because it diminishes the danger of overheating the interior as there is no heat radiation from a heated thermal buffer space. The balconies are only placed in areas without strong noise so that they always offer a calm recreation space. Once the window types are assigned, there’s a recursive function that analyses the stacking of the balconies that is required to contribute to the natural ventilation of the building. Only stacks of at least three balconies are admitted. The remaining balconies are reassigned and become openings of type A or B.
Then an other script places the exterior glass panels in front of the balconies. These glass panels have their own rhythm that is independent from the rhythm of the openings. The glass screen becomes an autonomous layer added to the perforated concrete facade. These two facade layers are working together and against each other at the same time. The resulting panel pattern gets analyzed and recursively modified within the script: Where there are columns of at least six panels on top of each other, the proportions of the thermal buffer required to produce a chimney effect allow an increasing depth of the balconies.

A heatmap illustrates the ventilation covering of each floor by analyzing the distances to the next ventilating window. This feedback allows to detect problematic zones with a lack of ventilation. In turn, parameters can be changed in order to achieve a satisfying result (red area limited to the core of the tower).

The south eastern facade turned out to be the most delicate in terms of ventilation covering due to it’s high percentage of type A windows. That’s why the fire escape stairs are located at this facade. The shaft of the stairs operates, like the stacked balconies, as a climatic device contributing to natural ventilation. The path of the stairs is defined a script within the engine: The stairs avoid balconies and cover the areas on the facade that are the least ventilated. It introduces a fourth window type, the stairs type, that fills the ‘gaps’ on the south eastern facade.

Further possible reactions to an unsatisfying heatmap feedback are relaunching the initial random window repartition, changing the number or the dimensions of the openings or change the ratio between small and large openings. The latter is usually set around fifty-fifty in order to create the typical facade image of the stacked balconies creating stepped shafts.

The plinth with it’s regular window interval is wrapped with glass panels as well. These glass panels are placed by a random based engine that takes in count three layers of information contained in a single gradient map (curtain effect gradient, noise protection, passage openings). A script places the panels by evaluating the map to calculate chance of a panel being placed for each possible panel position.

All these steps lead to the following facade proposal. The stacked balconies create a distinct drawing on the facade of the Piraeus Tower and turn it into an iconic landmark.



The concrete facade is made out of precast insulated elements, which are attached to the existing slabs. The exterior glass panels are hold in place by articulated metal beams that make the transition from the rhythm of the concrete facade to the rhythm of the glass panels. These beams penetrate the concrete facade and are fixed to the existing slabs as well. A cross bracing that allows to absorb the lateral forces is achieved by polygonal beams that follow the contour of the balconies joining the cantilevered beams.


Grasshopper canvas



Grasshopper screen shot


Grasshopper file
Pin up pdf A0 1
Pin up pdf A0 2


1:10 partial model





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