The Great Tropical Greenhouse
The Great Tropical House, completed between 1905 and 1907, remains one of the largest steel and glass structures in the world. Designed by architect Alfred Koerner and structural engineer Heinrich Müller-Breslau, it is considered Koerner's most significant work. Despite being over a century old, it continues to exemplify advanced architectural and engineering achievements of its time.
The building measures 60.04 meters in length, 29.34 meters in width, and approximately 25 meters in height, covering a floor area of 1,728m² and enclosing a volume of 36,200m³. Its central planting bed alone spans 1,000m², with an earth depth of 3.50 meters. Beneath the central bed is a cellar room containing radiators for heating, supplemented by three rings of heating pipes integrated into the glass roof. These pipes, with a small diameter, are discreetly hidded from view.
The structure features steel three-hinged arches on the exterior, while the glass façade is suspended on the interior. This design not only minimised heat loss but also optimised the building's aesthetic and structural integrity. For maintenance, three galleries encircle the interior and are accessible via the glass tower located at the rear of the building.
The steel structures of the greenhouses survived the Second World War intact. However, in the autumn of 1943, the blast waves from nearby bomb explosions shattered most of the glass panes. This devastation left the tropical plants exposed to freezing temperatures, resulting in the loss of the majority of the collection.
Despite this, some tropical plants reportedly survived, as dedicated employees safeguarded them in kitchens and living rooms until conditions allowed for their return. This resilience highlights the commitment of the staff to preserving the garden's unique botanical heritage during a period of immense hardship.
Reconstruction of the Botanical Garden's greenhouses began in 1949, with the Victoria House reopening in 1950. By 1958, nine greenhouses were once again accessible to the public. The reconstruction of the Great Tropical Greenhouse, a significant milestone, commenced in 1963 and was completed on 22 May 1968 at a cost of 3.45 million marks (equivalent to approximately 10 million euros today). The project included extensive modernization of the building's technical facilities.
During reconstruction, the original silicate glass roof was replaced with acrylic glass, chosen for its advantageous properties, including reduced UV absorption, lower thermal conductivity, lighter weight, and improved malleability, allowing for larger panes (1 m × 2 m). However, a key disadvantage of acrylic glass became evident on 31 July 1969, when a fire in the upper dome caused significant damage to the plastic glazing resulting in over half of the plant life being killed. The affected area was repaired before the onset of winter, and the greenhouse reopened in June 1970.
The heating system was also upgraded during the refurbishment. An air circulation system with 16 fans was installed in the vaulted cellar, distributing warm air via shafts at three different heights and cycling it six to eight times per hour. To maintain optimal humidity levels, a sprinkler system with 66 nozzles was added, capable of dispersing 130 liters of water per minute. Additionally, 96 high-pressure mercury vapor lamps of 400 watts each were installed to supplement lighting.
During the 1960s renovation, the heating system of the Great Tropical House was thoroughly modernized. An air circulation system with 16 fans was installed in the vaulted cellar, distributing warm air through shafts at three different heights and cycling it six to eight times per hour. To maintain adequate humidity, a sprinkler system with 66 nozzles was added, spraying 130 liters of water per minute. Additionally, 96 high-pressure mercury vapor lamps, each with a power of 400 watts, were installed to enhance lighting conditions for the tropical plants.
By the early 2000s, the Great Tropical House required extensive refurbishment due to deteriorating conditions. In March 2004, the building was temporarily closed when rusted ceiling light suspensions posed a safety risk. In January 2006, heating damage in the neighboring Victoria House nearly caused a catastrophic loss of plants, highlighting the urgent need for repairs to the Great Tropical House. Many of its cracked glass panes had only been temporarily glued, and the heating system was at risk of failure.
On 16 February 2006, the Berlin House of Representatives approved a comprehensive refurbishment project with a budget of 16 million euros. The funding was provided by Freie Universität, the Stiftung Deutsche Klassenlotterie, the Berlin Senate Department for Urban Development's environmental relief program, the BMBF's university construction program, and the European Union's European Regional Development Fund.
To prepare for renovations, the plants were relocated to other greenhouses and a specially constructed temporary greenhouse. Renovation work began in August 2006, focusing on structural repairs and modernization. The Great Tropical House was ceremonially reopened on 16 September 2009 and opened to the public the following day.
