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project type: article [map]
object:St. Mary - church by the sea type:church
location:Horumersiel-Schillig state:Germany
architect:Königs Architects, Cologne materials:brick-stone construction, glass
published:BFT 09/2015 page:58-63
 

Precast spire by the sea

Put the hat

One of only a few Roman catholic churches that were newly constructed in the past few years in Germany is located in Horumersiel- Schillig, a North- Sea spa situated directly by the Wadden Sea. Its spire is precast element that impresses with its sophisticated geometry.
In the wake of the dwindling number of Roman Catholic adherents in Germany, a newly built Catholic church would hit the headlines anyway - particularly if it is located in Northern Germany, which is rather a Prot¬estant stronghold. However, Horumersiel is home to one of the largest caravan camping sites in Germany, which is mainly frequented by holiday makers from the Ruhrgebiet, a predominantly Roman Catholic region. Past experience shows that people increasingly deal with religious matters when on holiday, which is why the old church attracted many worshippers, too.
However, this compact, chapel-like single-story building constructed back in the 1960s had been in urgent need of repair and refurbishment. Furthermore, an expert opinion stated that any repair of the old cast-in-place concrete church would probably have been more expensive than building a new church from scratch. This is why the Diocese of Münster, of which this region by the North Sea is part, decided in favor of the lauer option.
Königs Architekten, an architectural practice from Cologne, won the related architectural competition. They submitted a formal concept that makes the nearby sea "tangible" by an interplay of light and shadow in the church interior. For this purpose, a generously dimensioned rooflight structure was added whose individual glass panes appear in various shades. This roof is supported on many large-format roof girders. Taken together, both elements create a vibrant, multi-coloured shadow pattern on the curvilinear internal walls with their white plaster coat. This pattern changes constantly in sync with the movement of the sun; it actually intends to replicate the effect of light refraction in shallow water.
Cruciform ground plan, saddle-shaped section
Because of the difficult logistics of having to manage the North Sea project from Cologne, the Diocese requested that site management and supervision be taken over by the architects who came in second in the competition, Göken+Henckel based in Oldenburg. This constellation turned out to be one of the huge positives of this project since distinct formal ideas were merged with an exceedingly meticulous approach.
The ground plan of the church takes the shape of a Latin cross whose corners are rounded to achieve the light effects referred to above. This layout was "pulled up" in vertical direction and limited horizontally by a semicircular section along the eaves line. Furthermore, the building was given a saddle-like external appearance with two culminating points: the slightly projecting choir in the east and the significantly higher belltower in the west. In-between, at the lowest level of the glazed roof that has a pitch of two degrees towards the north, the central waterspout was placed as a precast element. The relatively strong pitch of the flat roof was necessary to prevent stagnant water from accumulating on the rooflights as a result of unfavourable wind conditions.
A ratio of 6 % of anthracite pigment was added to the mix for the precast element; the same applies to the architectural concrete ceilings in the main portal and side entrance areas. Supervising architect Dipl.-Ing. Michell Otto explains that this was the highest permissible ratio of pigment that could be added to these precast components, given the demanding weather resistance specifications. The element was produced at Steenfelder Betonwerk Johann Meinders GmbH at Westoverledingen, near Papenburg, and then inserted into the structural cast-in-place wall on-site. In the next step, contractors added the surrounding masonry consisting of brick burned under reducing conditions flush to the edge of the precast element. Roofers then lined the architectural concrete waterspout with sheet metal and connected it to the roof drainage system.
Precast element adds particular "flavour"
This church building has a very clear geometry. Its underlying design idea revolves around the stringent adherence to these simple symmetries even beyond existing standards that govern finishing design. A major portion of the shell is made from cast-in-place concrete that was lined with exposed masonry consisting of double-fired brick. To design a regular end to this relatively wide wall structure, it was virtually inevitable to include a fascia in the design. For this. reason, it would not have been possible to design die church tower that culminates in a sharp, oblique section - which is one of die core ideas of Cologne-based Königs Architekten - without additional intervention: a blunt spire including a small horizontal plateau (i.e. a fascia) with an open C shape toward the church would have been inevitable according to generally accepted construction practice.
This is why the design team decided to detail the entire spire as a precast element to be placed on top of the building shell exactly where the limiting roof pitch begins to intersect. The precast option also made it possible to find a structural solution to the excessive superelevation of the apex that resulted from the acute angle. Thus, in this area, the fascia that does exist in formal terms was inclined and elongated to an extreme extent, giving it an almost expressive appearance. This element was also produced by Steenfelder Betonwerk Johann Meinders GmbH - in an upside-down position, which meant that the horizontal surface of the concreting process became the final horizontal soffit of the element. No particular specifications were adhered to in terms of imperviousness to water because roofers completely lined the element that formed part of the roof edge at the finishing stage.
The facing brickwork was placed in the formwork and fixed directly to the precast element during concrete pouring. However, it had to be removed and relaid again in sonne peripheral areas because of significant devia¬tions from specified tolerances. Ultimately, the wall was to appear completely uniform, without any visible joint underneath the final element.
For the facing layer, the same type of brick as for the remaining cavity wall brickwork was used. Bricklayers had to manually cut the bricks in longitudinal direction. Bricks were first fixed to the precast element using an adhesive mortar and then pointed with the same exposed mortar as the masomy underneath. Lining bricks were cut straight even though the precast element has a curved external wall surface, which made it possible to compensate for any deviations from the curvilinear shape in the mortar bed.
Lifting the precast element into place
This relatively small church building was completed during a period of 29 weeks. Delays were mainly caused by adverse weather conditions. Some wind gusts were so strong that freshly applied pointing mortar was im¬mediately blown out again. Furthermore, in winter, icicles on the scaffolds grew horizontally rather than vertically due to storm impact. Several weeks passed before a calm day made it possible to lift the crowning precast element gently into place using a crane. After all, its placement had to be accurate down to the last millimetre - no second attempt was possible because the element was put directly onto a mortar bed.
Wolfgang Göken, architect and managing director of Göken+Henckel Architekten BDA, recalls having, sometimes, seen tiny imperfections even from a distance when approaching the site on the straight access road. However, these minute deviations created a tangible disruption to the intended symmetry, which is why they had to be corrected, to the resentment of contractors. "But this particular ‘flavour' would have been lost otherwise", Göken adds.
Robert Mehl, Aachen
http://www.bft-international.com