A Loam Structure on a Large Scale: Alnatura Office Building in Darmstadt

The Alnatura campus, which covers an area of 5.5 hectares, has arisen over the past few years on the former grounds of the Kelley Barracks in southwest Darmstadt. The company’s headquarters form the heart of the complex; its 10,000 m² offer space for up to 500 employees as well as a vegetarian restaurant that is located on the ground floor and open to the public. The client is specialized in the sale of organic groceries and has been pursuing an ambitious sustainability strategy for some time. Therefore, the request for an ecologically sustainable new building came as no surprise. At the same time, the structure was to cost no more than any other office building.

At first glance, the three-storey structure measuring around 90 x 40 m calls to mind an enormous industrial hall. This impression comes primarily from the west and east façades, which are completely glazed. In contrast, level-high windows alternate with massive rammed-earth walls on the north and south-facing longitudinal sides of the building. These walls conceal a reinforced-concrete skeleton that acts as the framework for an office concept that has, presumably, never been realized before: all the working spaces are accommodated in a single open-plan space that extends over all three storeys, including the skylit atrium. Only the furnishings and curtains delimit individual zones devoted to meetings and concentrated work. Other, closed-off conference rooms are located on the ground floor. As the client is a consistent proponent of desk-sharing, up to 500 employees can work at approximately 400 workspaces in the building. The open-plan office is topped off with an asymmetrical gable roof borne by huge glulam girders interrupted by a band of skylights that runs the length of the centre of the roof.

A Sandwich of Rammed Earth and Foam Glass

Each of the rammed-earth elements in the exterior walls measures 3.5 x 1 m and weighs around 4.5 tonnes. These were manufactured in a temporary field factory accommodated in an old parking hall for tanks; the hall was located on the lot and later torn down. The façades have an overall thickness of 69 cm, which comprises an external rammed-earth shell 38 cm thick, an inner shell of 14 cm and a 17-cm layer of insulation in between. The latter consists of foam-glass gravel made of recycled glass. In this case, the insulation was inserted into the wall elements while the loam was being rammed. The loam surfaces are visible on both sides of the wall. Inside, they have been treated only with a glaze of casein paint, which reduces abrasion. Exterior erosion-control elements at intervals of 30 to 60 cm will help keep the loam from washing away with rainwater.

Further information:

Call for tenders and object surveillance: BGG Grünzig, Bad Homburg
Landscape architect: Ramboll Studio Dreiseitl, Überlingen
Enery consultant: Transsolar Energietechnik, Stuttgart
Tamped clay construction: Lehm Ton Erde, Schlins