The closed cavity facade system from the Permasteelisa Group has been installed in Germany for the first time on the LEO building in Frankfurt.

The LEO building in Frankfurt is covered by a technologically advanced cladding created using operable modules of the closed cavity façade, engineered and produced by Gartner GmbH, the German subsidiary of the Permasteelisa Group. Gartner’s MFree-S closed cavity façade has helped transform the LEO building into a green building, with energy savings amounting to 60 per cent.

The MFree-S is a closed double skin façade, which has also been equipped with parallel opening windows for the first time anywhere in the world to allow for natural aeration. Bright glass fibre reinforced concrete units shaping the external cladding provide a contrast to the dark aluminium profiles of the window frames. Elegantly combining the new construction and the pre-existing building, the façade design creates a homogeneous striking appearance.

While refurbishing and modernising the building constructed in 1986, the Frankfurt-based architects Schneider+Schumacher also connected the two pre-existing opposing 17-storey and 9-storey wings by means of a 67-metre high diagonal building creating an overall U-shaped structure, and expanding the building’s floor area by 15,000sqm to a total of 47,000sqm. The window openings in the pre-existing buildings have been enlarged to allow more daylight to enter the office rooms.

Following the renovation, the final energy demand for heating and cooling in the LEO building declined by 60 per cent to about 90 kWh/m²a and primary energy demand for heating was reduced by 70 per cent to 28 kWh/m²a.

Gartner GmbH cladded the LEO building with a 10,000sqm MFree-S system, 13,000sqm glass fibre reinforced concrete units and 5,000sqm mullion-transom stick system and steel mullion-transom stick system façades. This building envelope is a key contributing factor for the LEED gold certification of the LEO building by the U.S. Green Building Council.

Key benefits of the MFree-S façade include fully closed cavity improving transparency while providing heat, sun and noise protection; highly transparent low iron glasses eliminate need for dark or reflective coatings for sun protection; 94mm façade cavity containing highly efficient sun protection systems with sensitive control and light control; hermetically sealed façade cavity preventing soiling of the inside of the glazing and the surfaces of solar control louvers; exterior glazing consisting of 6mm impact pane, with inside double glazing achieving a Ucw value of 1,0 W/m²K and a g value of 0.1 including sun protection; constant flow of dry and clean air flowing into the closed cavity units avoiding condensation; and dehumidified air preventing condensation on the external pane during variations in temperature.

The parallel opening windows of the LEO façade can be opened electrically to allow for natural aeration and smoke evacuation in case of fire. A sensor installed in the electric engine of the individually numbered windows reports every single opening to the building management system, which switches off the air-conditioning system of the relevant room during natural ventilation to minimise energy consumption. The sun protection louvers with light control, which are integrated in the façade cavity, can be operated even when windows are open.

Gartner has additionally cladded the LEO building with bright glass fibre reinforced concrete units partly with deep profiles and partly with smooth surface to create a changing surface structure for generating special light effects.