Stone

Although prefabricated concrete panels incorporating stone claddings are not something new -as an example to highlight the Hotel in Plaza España, designed by the architect Enric Garces, and built in 1990-; we want to draw attention on the appropriateness of the solution today.

As we mentioned in the wake of the SBG Schönburg building in Bern, the open-joint claddings are in crisis -not because of their performance, which nobody questions, but merely due to formal reasons.

Rain screen facades solved with thin claddings are a good solution regarding watertightness and the sun radiation protection. Besides that, they permit a wide range of image variations and so are supposed to be a gift for most of the architects. However, for some of them, all those open joint claddings give somehow a sense of lack of robustness; the wall is just a veneer, a vail. 

Composite façade panels are nothing new. They are there, waiting for the moment when the market will be ready to welcome them since the last decades of XX century.

The technology is already developed and essayed as those materials are perfectly used in many other applications. Maybe the cost, maybe the origin of the material (glass-fiber reinforced polyester), maybe we have not found yet its advantatges in building construction.

It is not easy to solve the entire envelope of a building, both façade and roof, with a continuous mantle of slopes varying from 0% to 100%. Tightness in the façade plane, where gravity acts in our favour, has been entrusted to geometry and drainage. However, this solution is not possible on the roof. The changes of slope in a topography of rounded ridges generates practically zero slope planes, which can only be resolved with absolutely waterproof materials.

This façade is not watertight and it is not airtight. Depending on the density and size of the stones, it protects against direct sun radiation but without managing the visual relationship with the outside. It considerably blocks the entry of light, gives privacy and protects from intrusion. If it is true that, together with a drained cavity, it would constitute a watertight envelope, but it seems that this is not the case here.

It is not possible to talk about facades without mentioning a very unique façade for the moment when it was built, and that even today continues being a reference.

The first point that draws our attention is the constructive system of own design, lightweight, based on a system of mullions (similar to a curtain wall). Despite the verticality imposed by the system, clearly visible from the outside elevation, the interior gives a fairly conventional image of blind parapet and horizontal windows. 

This is an excellent proposal for solving façade composition with a rectangular format checkerboard pattern (the blind and hollowed areas only touch at the apex), avoiding the presence of the slab.

Those who have faced this situation will know how difficult it is to unite at a vertex two openings on different floors, separated by a slab, without showing the thickness of this structural element.

The new building for the Dexeus Institute in Barcelona is one of the cases in which the openings completely divide the façade into horizontal strips. Consequently, the façade is not mechanically interrupted by the main structure but by the openings.

The Hotel Omm facade seems to us an interesting case study in many regards. It was a wise strategy to orient the openings towards the main avenue, Passeig de Gràcia, thus avoiding prying eyes from the building on the opposite side of the street as well as direct solar gain. Also, the bold materialization of this strategy involved transforming the outer layer of a rain screen façade into a series of lightweight walls that emerge from the façade as fish scales.