Freedom to Build Passive Houses: Art Museum in Ravensburg
The first museum at passive house standard in the world designed by the architects Lederer Ragnarsdóttir Oei (Stuttgart) is due to open in Ravensburg in March 2013. The new building clearly demonstrates that selecting the passive house option no longer automatically means saying good-bye to aesthetics.
Architects: Lederer Ragnarsdóttir Oei
Location: Burgstraße 9, D-88212 Ravensburg
Love triangles are known to be fraught with conflict. The new art museum does better than that: it is the result of a very harmonious love rectangle, according to the members of the Ravensburg project team. The parties of this rectangle included the City of Ravensburg, an art collector, a local building contractor (doubling up as investor), and – as the only "outsiders" – Stuttgart-based architects Lederer Ragnarsdóttir Oei.
The new construction was built by the contractor Georg Reich to the order of the City of Ravensburg and will be rented to the latter by the contractor for 30 years. The museum will primarily house the art collection owned by Gudrun Selinka and her husband Peter who died in 2006, which is mainly composed of works of German expressionism and the artist group COBRA of the period after World War II. The architects designed an appropriate home for this collection: a building integrated in the medieval city centre as though it had always been there.
Despite this cosy arrangement, the new construction had to satisfy stringent energy efficiency demands: the new art museum is the first museum in the world to fulfil the passive house standard. The investor was the primary initiator of this goal. On the basis of the argument that the operating costs would be significantly lower than for a standard building, the municipality was quickly persuaded by the plans. After all, the operation of the museum still means an additional cost of EUR 240,000 pa in the municipal budget – in spite of the passive house standard. Compliance with the passive house standard gives rise to an additional eight to ten per cent of the construction sum according to an assessment by the contractor's company.
New and yet familiar
The art museum is located at the southern edge of the historic city centre; immediately opposite, the terrain rises up sharply towards the castle hill accommodating the Veitsburg. The location was one of the less frequented spots in the city centre, but this could soon change: during the past four years, a "museum district" including museums dedicated to the history of the city, economics and toys, has been developed within a radius of 100 m around the new building. The art museum completes this area as the final and largest member (and only new construction) of the quartet.
The new museum building thrives on the tension between familiarity and subtle surprise effects. If it wasn't for the still shiny copper sheeting at the window frames and rainwater ducts, it would be hard to allocate the building to a specific decade. The façade material – 200-year-old bricks from a demolished Belgian monastery – looks timeless from the very first day. The minimal entrance yard with its "windows" of slanted glass louvres towards the street is obviously a child of the 21st century. From the south, the tall, closed museum structure calls to mind a warehouse that has lost its way from the Baltic Sea area and found a home in Upper Swabia instead. But even this image is disrupted again – through the wave-shaped edge of the unusual barrel roof at the upper façade end, which is referred to again later.
Stringent concept on cramped site
With 800 m² of exhibition space, the art museum is among the smaller museums in the country. (For comparison: the Brandhorst Museum in Munich, also a publicly financed collector's museum, is four times as large.) The space is split over three levels: on the ground floor, 200 m² are available for special formats – including a kind of "Artist in Residence" programme in which external artists are invited to take a look at Ravensburg. On the first floor, 300 m² present changing extracts of the Selinka collection, while the equally large second floor space is dedicated to showing changing exhibitions.
The architects should be complemented for the fact that they developed a very stringent spatial concept and circulation design in spite of rather difficult conditions: the plot is completely built on and the street next to it has an incline of up to 10%. They placed the largest possible rectangle in the polygonal plot of land and stacked three such rectangles on top of each other – except for the ground floor, where the façade of the room for museum pedagogy is slightly slanted to follow the course of the road. The remaining areas were used for two stairwells, an elevator shaft and the minimal entrance yard. WCs, storage and administration areas are located in the basement.
Good-bye to the "white cube"
The building is not accessed – as would instinctively be expected for such a building – from a street corner, but from the highest point of the plot. Inside the building, the spatial concept also has several surprises in store despite its simplicity. The most remarkable of these is the room on the second floor, where visitors are confronted with vaulting made of conically shaped, inversely arranged, brick barrel roof sections. Their horizontal thrust is offset like in a folded plate construction; the vertical loads are transferred to the two longitudinal walls through steel I-beams at the groins.
This can be considered an affront against the common dogma in museum construction that the room should let the art it contains dominate completely and reduce itself to a neutral "white cube". In this regard, Arno Lederer makes reference to the creative process of most works of art, which after all originate from paint-spattered untidy artist studios, and could hence be considered out of place in a clinical environment.
Trust down to the details
Lederer feely names the sources of inspiration for his design – and many a design in the past: Hans Döllgast for the attitude towards the city, Sigurd Lewerentz for the brick vaulting, Le Corbusier for the voluminous water spouts at the roof edge (which of course only serve for emergency drainage) and Carlo Scarpa for the black niche in the wall immediately behind the cash desk illuminated naturally from above.
The desk – as well as the shelf in the foyer wall diagonally opposite and a wash basin in the museum pedagogy room – is made of fair-faced concrete connected inseparably to the shell of the building. The clients also relied on the taste of their architect as far as the selection of the foyer seating (for events) was concerned. Lederer responds to this show of trust by praising the good collaboration and calling the client an ideal investor. And it doesn't even seem to be a case of warm yet empty words at all.
Years ago, Lederer Ragnarsdóttir Oei entitled an exhibition of their work "Inside is different from outside" ("Innen ist anders als außen"); the very same attitude is evident in their Ravensburg project. The interior rooms not only have few windows, they are virtually (day)light shy, even in places where this would not have been necessary for reasons of conservation of the exhibits. There are basically only two opportunities for the visitor to turn his or her gaze away from the art and let it wander into the distance: a large square window in the museum pedagogy room offers a view of an alley, and a window at the stairhead provides a framed view of the opposite castle hill.
The artificial museum lighting oscillates between subdued restraint and intrusiveness. Flush wall-integrated LED lights covered with matt glass panels supplement the daylight illumination in the stairwells. In addition, there are discreet LED "light seams" in the window reveals just behind the window frames. Clearly less unobtrusive are the cross-shaped ceiling lights in the museum pedagogy room as well as the rather large "light scoops" on the walls of the second floor, designed to highlight the unusual barrel vaulting.
A passive house almost without any solar gains
When Lederer Ragnarsdóttir Oei won the architectural competition held for the new museum building in 2009, there was no mention of a passive house standard. Yet the architects did not have to modify their design significantly for the sake of achieving greater efficiency – on the contrary, they made the design less rather than more favourable for a passive house, according to Arno Lederer. A previously planned large window in the uppermost exhibition area was cancelled after the competition. The solar gains that this would have made accessible, were counteracted by daylight entering the exhibition areas – always a problematic issue for museum curators.
On closer inspection however, achievement of the passive house standard demanded a lot of extra work with regard to development of details and calculations. It soon became evident that a compact, well-insulated "box" is only half the battle for a passive house. The solar heat gains, in this case almost completely lacking due to the small number of windows, are just as important. The required heat is instead mainly delivered to the building by the expected 25,000 visitors per year – however also in midsummer when the building could normally do with cooling.
Sustainability also in material selection
The outer walls composed of two layers (concrete on the inside, second-hand clinker bricks on the outside) were insulated with 24 cm of mineral wool. Together with a rear-ventilation gap, this means that the distance between the leaves of the wall is 30 cm, with a total wall height of 17 m. The wall ties therefore have to offer top performance in terms of stability, while keeping the thermal bridge effect as low as possible. The planners accomplished this feat by means of a newly developed tie with a lower steel content. Also newly developed – and specially certified by the "Passivhaus Institute" – is the copper-clad revolving door at the entrance.
Arno Lederer does not however wish to see the subject of sustainability reduced to an energy aspect only. Instead, his credo is to move away from a production society towards a reutilisation society. The idea of cladding the new building with second-hand bricks originated from the architects who also obtained the material themselves. Lederer Ragnarsdóttir Oei have access to suitable sources on account of two previous construction projects that were clad with similar bricks.
The types of materials not represented in the building are also noteworthy. Paintwork and coatings were largely done without, copper was used instead of aluminium wherever possible, and even at the entrance, the job of the ubiquitous synthetic fibre mat is performed by a grid made of (still shiny) copper integrated in the floor. A further striking detail: the façade-integrated, open and very broad rainwater chutes made of copper that replace the customary closed rainwater downpipes.
Hot and cold thermal energy from below
As far as the building services equipment is concerned, implementation of the passive house standard profited from the fact that many of the installations required for high efficiency were already in place for reasons of conservation of the exhibits. The conditions in the exhibition rooms have to be kept very close to specific target values (20 °C room air temperature and 50% +/- 5% humidity) throughout the year. The building is therefore equipped with a ventilation system with recovery of heat and moisture, the air volume of which is regulated as required via a flow control valve. A displacement ventilation system was realised in the rooms to avoid draught effects. The air is fed to the rooms at the base and withdrawn again at the suspended ceilings. On the second floor, where this was not possible because of the brick vaulting, the vents are hidden behind the wall lights.
The building is heated and cooled by means of temperature control of the concrete core of the 40-cm thick ceilings. The system is connected to a heat pump and eight geothermal borehole heat exchangers located at a depth of 100 m. Instead of a customary electrical heat pump, a gas absorption heat pump was installed in the building, since this is reversible and can therefore also be used for cooling (as an absorption cooling unit) in summer.
The base load of heating and cooling is always covered by the concrete core temperature control system, which is normally operated with a flow temperature of 22 °C. It therefore functions as slight room heating in winter and cooling in summer even without any temperature change. To cover peak loads, the incoming air can moreover by heated or cooled using the heat pump.
Project participants, data and facts
Client: Reisch Bau GbR, Bad Saulgau
Project manager: Katja Pütter
Energy concept/Heating/Ventilation/Air-conditioning: Herz & Lang, Schongau; Vogt & Feist, Ravensburg
Structural analysis: Ingenieurbüro Schneider & Partner, Ravensburg
Electrical planning: Sulzer GmbH & Co. KG, Vogt
Construction period: 2010 to 2012
Ground-breaking ceremony: 21.09.2010
Topping-off ceremony: 10.05.2012
Gross floor area: 1,900 m²
Gross volume: 8,300 m³
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