Green benefits

The designers of the new global headquarters for the energy giant Endesa in Madrid used laminated glass with structural or advanced polymer interlayers for a unique glass flat roof, in an example of deriving maximum energy efficiency, sustainability and a striking design.

The 32,300 square-foot roof tops a huge glass atrium that uses a natural ventilation system. The London office of the New York-based architectural firm Kohn Pederson Fox worked with Rafael de La-Hoz Arquitectos on the project, which brought together 1,300 employees previously scattered across several Madrid locations. The client sought climate control for maximum comfort and as much natural daylight as possible.

The design was based on the Spanish tradition of an internal shaded patio or courtyard, but updated for a modern solution and today's business environment, said Cristina Garcia, senior associate partner at KPF. The atrium, which acts as transition and social interaction space and serves as a buffer between the external environment and the thermally controlled office space, had to provide daylight but also energy efficiency in an environmentally responsible manner.

"Glass was the only way to get this big, central space to work aesthetically," said Garcia. "Yet the glass could obviously only be used if it was totally safe. There could be no risk under any circumstances of panes of glass falling out onto the people in the lobby."

The construction required exceptional strength and rigidity, in a trapezoidal shape rather than a domed or double-point (triangular) construction. It is believed to be the first time such a large suspended low-slope, single-pitch roof has been built entirely with glass.

A traditional PVB interlayer would have deflected under the accumulated load of such a large roof, Garcia said. The solution was to use the new advanced interlayer to provide enough strength so the suspended laminated glass could be fixed, with a series of drilled points, to a steel grid.

The roof bears stresses including maintenance workers walking on it to clean it, heavy winds and snow loads. If individual panes break, the interlayer keeps the panels intact and adhered to the rest of the structure. The interlayer retains strength even in intense summer heat.