INTRODUCTION. The requirements set down by the management of the labour unions Union General de Trabajadores and Comisiones Obreras (Syndicate Headquarters) are based on the total independence of the use and layout of the spaces assigned to each one of the unions, the reason why the project features two independent accesses and office spaces that are totally differentiated for each one of them. The only share the assembly hall and the installation spaces of a general nature, for obvious reasons of dimensions and technical efficiency. Besides the conditioning factors mentioned above, equality in surface and orientation for each one of the labour unions is a basic requirement. In this way, the ground floor is destined for the general spaces of access, control and reception of users, plus the more generic administrative activities, besides containing the assembly hall that is common to both unions, for evident reasons of ease of access. The first and second floors are fully assigned to the administrative spaces of each one of the unions. The complexity of both unions running independently, equally separated and joined by the light, has been possible thanks to the orientation, as the situation of the building on the plot coincides with the north/south orientation in its diagonal, a crucial element in the internal order of the spaces in this project.
JUSTIFICATION OF THE COMPOSITIONAL SOLUTION ADOPTED. The basic conception of the building starts from a concrete plinth that houses the common zones and accesses. On this rests a metallic containing the administrative zone, which is projected symmetrical in the diagonal as this is the north-south orientation and thus provides each labour union with the same hours of sunlight during the day and with the same available surface. In this way, on the basis of the premises expressed above, the building is designed as a ground floor operating as a general plinth inside which is the common assembly hall and the general distribution and reception spaces of each one of the unions, composing a space over a triple height that houses part of the general concrete plinth and the distributor space of the offices of the first and second floors. In this main distribution space there also appears on the ground floor a common courtyard adjacent to the entrance of the space assigned to each one of the unions, plus a second courtyard situated on the plinth of the first floor and playing with the visual union of the two distribution spaces of each union, allowing the light to penetrate and light up each main distribution atrium. This means that both general distribution spaces of each union are joined by the light and the visuals. The first and second floors, with a metallic structure, are recessed in their floor plan with regard to the limits of the concrete plinth of the ground floor and are destined only for administrative spaces and offices, always with facades giving to the outside and with the openings protected by fixed awnings in perforated sheet metal that can be orientated according to need, while the interior spaces over a double and triple height are left to the layout inherent to each labour union. The analysis of the requirements in the programme of uses, together with the surfaces assigned to each one of the labours unions, and after studying the possibilities offered by the site, led to the construction of the new headquarters for the labours unions. The building is aligned with the facades of the straight angle of the plot and forming a corner on said angle, maintaining the sharp corners of the site free for surface car parking also independent from each other. To sum up, the building is approached as two juxtaposed edifices. A first volume of larger dimension in reinforced concrete and a second one, in more reduced dimensions, which is juxtaposed on the first one. Besides the dimensional differences, the basic duality of the building, both are differentiated by the treatment and consideration of the openings: in the former there are hardly any and they are reduced to the entrances from the outside, while the latter has a protection grille that also operates as the organisational modulation of the openings, which are more numerous and smaller in dimension than in the former.
GENERAL CONSTRUCTION CHARACTERISTICS. The ground floor is composed a plinth built from screen walls in exposed concrete. The first and second floors correspond to the metallic box formed by heat-profiled pillars in the shape of a closed box and an enclosure in metallic fretwork sheet metal on the outside, with awnings in micro-perforated fretwork sheeting. Inside, the enclosure of the box on the first and second floors, together with the distribution atrium, is resolved by means of a cladding in laminated U-Glass and wood panelling lacquered in white. All the internal partitions of the offices are flexible in their installation and assembly system in order to facilitate any future changes in the use of the building, and so this flexibility has conditioned the metallic façade in the layout of a large number of vertical openings.