The Y Lego concept, submitted by Sebastian Irarrazaval Architects, Chile, is organized around three ideas:

1. The proposal of a modular unit that maximises cross ventilation by eliminating corridors and providing double orientation to every space.
2. A building structure that can adopt different configurations, much like Lego® blocks, in order to adjust to different sites conditions and urban objectives.
3. A structural approach that maximises the steel's potentials for lightness and high performance under tension.

Since the construction site is located in a humid tropical region of Brazil in the city of Recife, the general objectives for Y Lego are to improve thermal conditions through abundant natural ventilation, to reduce solar radiation and to raise the building above ground level to reduce humidity. To achieve this, a 3.5 meter module with a "Y" shape plan enabled the architects to limit corridors and to have a double orientation for every space. The spaces are of similar design throughout the module, each having a core where services are allocated, but allowing flexibility to reconfigure the room in a variety of ways to suit its use. Adjustable to different sites conditions and urban objectives.

Given the need to create a prototype than can be replicated in different sites Sebastian Irarrazaval proposed an open unit than can join with other units in different shapes and create infinite configurations. The module's "Y " shape works like Lego® blocks. This flexibility allows the building to be structured to fit the demands of different sites. Given the poor soil conditions of the Recife site, there is a need to minimize foundations. Consequently, the architects propose a hanging structure criteria, where the stories are hung from beams located at the top of the building, limiting the building's contact with the ground. These beams distribute the building's mass among three concrete cores.

A "Y" shape plan enabled the architects to limit corridors and to have a double orientation for every space. It works like Lego® blocks, providing flexibility that allows the building to be structured to fit the demands of different sites (example left).

A System Of Open Pores The central principle undertaken in the concept is that of passive strategies for reduction of heat absorption that will minimise the need for supplemental cooling systems. The initial concept does not consider mechanical cooling systems or the installation of photovoltaic or eolic systems. The building's double wall design, made of perforated steel plates, enable these systems to be installed later within the walls, reducing initial construction costs. In general terms the project fulfils the above mentioned principle in two stages:

The complex is conceived as a large system of individual open pores, including several patios that allow ventilation without major interference from surrounding pores. By this means natural ventilation passes through these various pores as well as under the building. The air then travels upwards by way of the patios which act as thermal chimneys. The patios, evenly distributed throughout the building, allow the ground to be dried when the sun is directly received, creating an evaporative cooling effect that can cool the module interiors.

The site's development includes a mixture of high- and medium-rise buildings within the complex to allow conduct of prevailing winds throughout the complex, further enhancing natural ventilation.

Double-skin perimeters prevent direct sun radiation yet permit ventilation.

2) Individual dwellings: Each dwelling is designed to include a large perimeter to support natural cross ventilation. This perimeter is projected as a double-skin system that prohibits the reach of the direct sun radiation over the facades, yet permits ventilation. On the other hand, this is designed to house any auxiliary conventional equipment (mentioned previously) for ventilation and/or air-conditioning within the gap between the two skins, eliminating aesthetic damage to the facades. The minimal use of partitions within the interior further supports this cross ventilation.

The structural challenge posed by the building's architecture is that all the resistant elements have to be pure and have a structurally precise function. The building has either six or 13 stories for housing. Its vertical structure is based on structural walls of reinforced concrete allocated both in the central core and on the extremes. The horizontal structure is composed of two primary longitudinal W shape beams supported on the concrete wall at the top of the building. Consequently lower floors are attached to hangers suspended from the beams in the upper level. Also in this level, transversal steel beams are supported by the walls in order to guarantee good performance of the cantilevered elements.

For the same purpose, diagonal beams are located in the central part of the extremes. The primary beams are 50 cm high by 30 cm wide and can support between six and seven stories. For the 13 story buildings, it will be necessary to place two primary steel beam systems: one in the middle and the other on the top of the building.

Composite slabs on steel decks are used for the floors to create rigid diaphragms that distribute the dynamic forces. These diaphragms are supported on secondary steel beams in every floor to avoid large displacements. Taking into account the low bearing capacity of the site's soil, the structure is anchored using a foundation system of three slabs, one central and two extremes, connected with foundation beams. For the six story building, the slab is around 50 cm high and for the 13 story building, it is 80 cm high. Pillars can be included, but it is expected that the foundation beams should be rigid enough for the stability of the building.

Construction techniques are simple, mainly dry and based on the repetition of regular elements. Non structural elements are composed of dry wall, and module floors are finished in ceramics.

Each module has a core where services are allocated, and walls are movable to flexibility in reconfiguring the room in a variety of ways to suit its use