Leibniz Institute for Astrophysics

Named after the first woman to discover a comet, the astronomer Maria Margaretha Kirch, the building is divided into three cantilevered arms that blend into the terrain while respecting the natural tree structure. The silhouette of the extension appears smaller than the room programme would suggest due to the base storey, which is partially dug into the slope, and the staggered upper storeys on top. From the outside, the entrance area appears to be single-storey - and therefore no higher than the neighbouring buildings, while the street-facing elevation is three storeys high. This means that the extension does not compete visually with the existing buildings on the campus. In addition, the shape of the building, which dovetails with the park, offers a further advantage: there are landscaped areas between the arms of the building, so that the rooms benefit from a high level of natural light with all-round views of nature

Behind the façade, the room programme is spread over three floors, ensuring good networking, short distances and optimal lighting for all rooms. The majority of the rooms consist of individual offices. In addition, the building integrates a canteen, a conference room and exhibition and archive areas such as the exhibition room for the observatory's historical equipment. All public areas are grouped around the centrally located foyer, which also provides access via a wide staircase to the two other floors with the research units, meeting and communication zones located there.

Due to the hillside location, the supporting structure of the new building, which is embedded in the landscape, was constructed in reinforced concrete and the base storey was clad in limestone. In the interests of sustainability and to create a link to nature, the architects supplemented this material concept with a timber façade as the outer shell of the upper floors. Wood was also used for the interior fittings and furnishings of the building, e.g. in the form of wooden frames for the windows in the public areas, whose colour scheme was developed in collaboration with the artist Friederike Tebbe.  The outer skin, glazed with a Keim pre-greying, adapts to the colours of the surrounding forest and anticipates the final colour scheme of the building.

In order to operate the extension as sustainably as possible, the roof was designed as an extensively greened flat roof and a photovoltaic system was also installed. This supplies the institute with regeneratively generated electricity. In addition, a geothermal system coupled with a heat pump draws energy from the ground via pipe systems laid under the forecourt to heat the premises. Rainwater seeps away directly onto the site via infiltration systems.

The mullion and transom façade of the Leibniz Institute combines several functions in one: it serves as a building envelope, ventilation opening, sun protection and fall protection. Its complex structure is made up of a series of different building elements, louvres, grilles, horizontal and vertical formwork, frames and recessed infills. This variety creates a visually small-scale appearance and at the same time fulfils a number of functional requirements. Ventilation, for example: large, almost floor-to-ceiling windows allow views, but are only opened for cleaning. Narrower, adjacent window sashes can be opened to allow fresh air in and exhaust air out. This solution allows continuous ventilation without wide window sashes colliding with desks or other furniture. Wooden louvres arranged in front also act as fall protection.
The basic principle of the façade combines frames with deeply recessed, different infill panels made of silver fir. While the frames are made of solid structural timber with a cross-section of 15 x 10 cm, the infills are made of 21 mm thick profiled timber in two different widths. The two materials were sourced from two different suppliers - Häussermann GmbH & Co. KG and Burger Holzwerk GmbH - were pre-greyed in the respective factories and delivered to the construction site, where the timber was cut to length and assembled.

In order to study and check the effect of the pre-greying and the changes during the ageing process, the architects had already built a 1:1 wooden façade model before construction work began "We left this outdoors for three years under natural weathering conditions. To this day, you can't see any ageing process or the removal of the pre-greying and the ageing process merge seamlessly, so that no difference can be seen between the treated surface and the natural patina," reports architect Ivan Reimann, the architect responsible for the project and managing director of Thomas Müller Ivan Reimann Architekten.

Häussermann first processed the profiled boards with a planing tool to achieve an optimum colour design for the façade infill elements. The cross-window louvres were produced with a rough-sawn structure on all sides with the requirement "visible on four sides". Pre-greying was then carried out with a single application of Keim Lignosil-Verano in the colour 4875, a silicate greying glaze. It simulates the greyed patinated surface that results from years of weathering of natural wood. As the product is subject to natural ageing, the visual differences caused by uneven weathering of exposed and protected surfaces are practically imperceptible. The surface of the solid structural timber was planed and subsequently profiled. The different colour application process resulted in a different appearance of the glaze compared to the profiled boards and lamellas. A second colour treatment was therefore necessary. The ends of the timber were repainted on site to round off the appearance.