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© SHF / Stephan Falk
Windows on the Lustgarten side

October 11, 2018

A thousend windows for a palace. Technical requirements for perfect vision.

by Hans-Dieter Hegner

The impact made by the Baroque facade of the Berlin Palace in its urban setting was and still is one of the main motivations for reconstructing the historic building. The design by architect Franco Stella envisions the original facades being reproduced with great accuracy. The eastern aspect, by contrast, is pleasantly understated, with an impressive composition of high-quality precast exposed concrete elements made from white cement.

The appearance of the facades will be dominated by windows. The building has over a thousand of them – roughly half of which are historical in design, the other half, modern. They are generally double box windows, which means they can overcome particular technical challenges. From the outside the historical windows function as part of the recreated facade, but inside they have to fulfil all the modern requirements for energy efficiency, daylight levels and security. These windows are vast: the largest window on one of the entrance gates, for example, measures 5.5 by 9.5 metres. Wooden windows of this size usually demand sustainable materials, good planning and special finishing and mounting. Equipped with electric motors for opening them automatically and controlling the various blinds or curtains between the panes, these windows are full-blown machines.

The reconstructed windows are, of course, brand new. Their design had to tick a number of boxes. The architectural stipulations for manufacturing and materials were just one side of the coin; the windows also had to meet the strictest requirements set by the Staatliche Museen zu Berlin concerning the interior climate, UV protection and light management. Sensitive Asian cultural goods made of paper or textiles cannot tolerate any sun. Moreover, it was important to safeguard the valuable exhibits from the risk of break-ins and ensure that they could be monitored – not to mention the high degree of soundproofing required for the Humboldt Forum; after all, museums and event venues have to be sealed off from all the noise of a large city.

Workmen installing the windows. © SHF
View on the windows of the Lustgarten Gate, April 2017. © SHF/Stephan Falk

But the construction of the windows also had to satisfy technical requirements that would make them fit for the future. Ultimately the Palace aims to do its bit for energy efficiency by shaving 30 per cent off the levels specified by the German Energy Saving Ordinance. That means the windows have to be exceptionally efficient at saving energy. A high degree of resistance to wind and driving rain was critical, not only for the windows themselves but also at the point where they join the facade. In addition, the Stiftung Humboldt Forum, which will be running the building, needs to ensure that the windows will hold up to constant use and be easy to maintain.

The first key consideration for the reconstruction was the selection of materials. It was clear from the start that the windows would be made of laminated white wood. Various woods were tested not only for their resistance, bulk density and robustness, but also for whether they discharge resin and can be preserved. Finally it was agreed to use European white oak. The wood was certainly slightly more expensive than foreseen in the budget, but later generations will thank us for choosing a material that is so sustainable.

With the fittings, it was important to choose ones that could be used up to 20,000 times over a lifespan of at least seventy years. Personally, I am assuming that they will still be working perfectly in two hundred years.

In order to ensure that the windows are not just aesthetically pleasing but also high-functioning components of the Palace, the Stiftung Humboldt Forum has commissioned a surveyor to supervise the project, from the initial choice of wood through to the final mounting. So now we’re absolutely certain that the view from Berlin’s most beautiful windows will generate the most wonderful emotions, delighting their users for many years to come.

Hans-Dieter Hegner was appointed to the Executive Board of the Stiftung Humboldt Forum im Berliner Schloss in early 2016 with responsibility for all construction-related matters. With a background in structural engineering, he previously headed a division in the German Federal Ministry focusing on civil engineering, sustainable construction, construction research, and other issues related to building culture.

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