Considered as one of the most important architectural construction works of the 20th century, its merit lies in the fact that, from an engineering and architectural point of view, never had a suspended building been built with those characteristics before. At the 1975 World Conference on Architecture and Public Works in New York, on prestressed concrete, the Colon Towers were considered as "The building with the most advanced construction building technology up to 1975," using this material.
The Colon Towers are on an irregular 1,710 sqm site of a specifically important location, the center of Madrid, and the background for important urban views. The project was expected to be adapted to a predictable urban context that never arose due to successive changes of criteria by the City Council.
To compensate the expropriations on the Towers' allotment, the City Council decided that "the building should be an architectural unit with a powerful verticality." Given that the municipal regulations set a volume limit but not an explicit height limit, Estudio Lamela found that if a single tower were to be built as suggested by the City Council, the streetscape would have been seriously harmed by the insertion of a building with massive proportions. For this reason, our Studio proposed the duplication of the volume to lower its height. Ultimately, following long debates with the City Council, it was finally accepted that the project would consist of two lower towers instead of one tall block.
The towers were initially to be primarily for residential use, although permission was granted for supplementary business uses on the lowest floors. The analysis of the program s requirements and its adaptation to the existing allotment showed our Studio that there was an irresolvable contradiction between the requirements brief and the use of conventional structures. This problem, unsolvable by conventional means, led to the apparently utopian idea of suspending the towers, which would permit a double structure by means of which the two parts could be made independent. Finally, the complex consisted of three almost independent buildings: the plinth and the two towers.
The structural system of towers was designed entirely in reinforced concrete, using high-resistance post-stressed concrete. This enabled the Studio to move away from the most widespread technique for suspended building that used steel structural headers, and instead adopted a suspended architecture solution: the slabs forth standard floors are supported around the perimeter by external braces which are not in traction as in the case of hanging architecture, but instead are compressed against the post-stressed concrete structure of the header beams. This upper structure, inside of which is the equipment machinery, bears the load of the 21 suspended slabs, transmits it to the core where it finally descends to the foundations in the ground.
The City Council ordered works to stop after they had begun and demanded their partial demolition, alleging that the Towers exceeded the maximum permitted height by 9 meters. Estudio Lamela argued that the disputed meters were part of the structural headers of the suspended system, and that as structural elements, they were permissible. Because of losing the suit, the City Council had to compensate the developers for their lost time and decided to grant certain concessions, permitting the primary use to be for offices and allowing an otherwise unlawful portal on the basement level to give the ground floor further commercial usage.
The original walls were bronze-colored prefabricated bent anodized aluminum sheeting. The window frames were in the same material and color, with light bronze-colored glazing. In 1989 Estudio Lamela took on the remodeling work for the Colon Towers and the facade became a double skin, with a new colored glass facade set flush with the inner plane of the tensors to improve the its occupancy conditions, the building's thermal and soundproofing as well as improving its energy control. The main reason for the renovation work, however, was the need to install an exterior fire escape for compulsory safety reasons. This additional staircase was set between the two towers, servicing a series of escape walkways that connected all the floors.
Estudio Lamela set out to reshape one of its most emblematic buildings while attending to the requirement of its possible reversibility, that is, an operation that would enable the owner to restore the original image of the towers if so desired.