Facade redevelopment

Due to grave civil engineering physics and construction defects, the facade cladding of a secondary school in Berlin had to be completely redeveloped - while the school remained open.

More than 30 years ago, the vocational training system was rearranged and a range of courses were bundled as of class 11 (16 -year-olds) according to occupational fields in various secondary school centres. Today the national capital has 35 secondary centres and a further 18 vocational education centres. The small, often out-of-date, locations were often replaced by spacious and modern school facilities with workshops, labs, a library and media centre. Training companies and learning offices were formed too. The locations also each had a café and a canteen to cater for the students. In 1979 the secondary school centre for car technology was formed at Gierkeplatz in Berlin. This educational centre offers training courses to students from dual vocational training up to achieving general qualifications for university entrance in its role as a college, vocational school, technical secondary school and vocational secondary school.

The metal facade which was constructed back then consisted of crimped aluminium plates and rounded blue window profi les and distinguished the building clearly from its environment. The listed 1970‘s building had its 2800 sqm facade cladding completely and energetically refurbished due to grave construction and civil engineering defects. The building owner decided to use the refurbishment concept developed by the architects Huber and Staudt, Berlin. It intended a curtain-type, heat insulated and rear-ventilated facade construction with horizontally layered U-shaped aluminium slats. Varying heights and alignments of the slats in a light bronze tone emphasised the dynamic of the building volume. The window hinges in a dark bronze tone are recessed about 150 mm inwards. This way, the planners achieved a contemporary architectural look without losing the link to the original facade.

The construction task

The reasons for the necessary refurbishment were an insufficient, and, according to today‘s standards, almost ineffective insulation of the outer walls as well as corrosion damage to the reinforced concrete walls. The old facade insulation only consisted of light wood wool building panels with an approx. 30 mm insulation layer made from foam polystyrene. The walls had excessively low concrete coverage over the steel grate reinforcements - grates were even exposed and already badly corroded. The reinforcement located too close to the concrete surface corroded as well and resulted in the concrete spalling in some wall areas. Furthermore, there was also the risk that the corrosion damage could have a negative effect on the static requirements of the wall construction. All windows had to be replaced too as part of the energetic refurbishment according to EnEV-standards. The next task was to reconstruct the old facade and to carry out extensive concrete refurbishment. A specialist company exposed the corroded steel reinforcements, derusted them using a sand blaster and applied a protective coat. Finally, the necessary concrete surface layer had to be applied in order to prevent further corrosion damage. It was only then possible to begin with the work for the new metal facade. BOEHME^® SYSTEMS GmbH from Boxdorf near Dresden received the contract to carry out the work. The company was founded by Holm Böhme in 1984 and manufactures historic building ornaments as well as shingles, diamonds and modern variable facade systems in its own production facilities. Therefore, BOEHME^® SYSTEMS was in a position to implement the architect‘s individual requirements with regards to the facade construction design. For many years, Holm Böhme has been working in cooperation with the civil engineering offi ce Andreas Dähn (Dresden) on complex building projects like this, both nationally and internationally. Dähn was responsible for the entire work planning and manufacturing preparation as well as the construction site coordination during the two-year construction period.

Attach invisibly

Andreas Dähn had several challenges at once to overcome for this project. „There was not only too little concrete coverage but also enormous measurement tolerances due to the very negligent construction when the original shell was constructed. We had to compensate within the facade construction up to 150 mm discrepancies for construction parts of approx. 20 meters in length. In some parts you could see that once the concrete worker had emptied his wheel barrow load, he took a „creative break“. The planning of the fixed and floating points of the building parts was very demanding due to the complex interlaced facade surface with numerous interior and exterior corners and curves. Both building movements as well as temperature related extension movements had to occur without causing damage or noise. The different extension characteristics for straight and curved surfaces was another factor that we had to consider,“ explains Dähn.

The facade construction consists of four parts in principle:

1. fixed and floating points
2. the insulation, 160 mm, concealed on one side and water repellent
3. stud holders
4. facade elements

The facade elements are of a modular design and manufactured in dimensions of approx. 4.00 x 2.50 m in the workshop. The individual modules consist of three to six support profiles which are each fitted with an average of forty individual profi les. BOEHME^® SYSTEMS developed a click system which makes it possible to simply slot the individual profiles in place since neither studs, screws, staples or holders are to be visible on the surface.

Planning, measuring, designing

The architects split the building project into the seven building sections whilst the second and fourth building sections are curved with different radii. The arrangement/distribution of the profiles had to run around the entire building body from the first to the last building section. The distribution of the horizontal facade elements was carried out in Flemish bond in order to fit windows and other penetrations - both optically and technically correct. These cladding patterns distinguish themselves by their variable latticing. „Orientation points for the distribution were the height distances between window sill and window lintel as well as the floor blanket heights. A range of different surface layers with 50, 70, 90 and 110 mm were used. Four different window levels and, in addition, a wide range of window sizes did not make it easy to stick with the horizontal joint appearance over a length of approx. 300 m from the first to the seventh building section. We arranged five to seven millimetre wide vertical butt joints between the facade modules in order to enable expansion movements of the cladding elements. The aluminium profiles are simply covered at the horizontal joints. This way we achieved an optically almost closed surface, with the exception of the unobtrusively designed vertical expansion joints, without hampering the extension and building movements,“ explains Andreas Dähn.

After disassembly of the old facade construction and the expensive concrete refurbishment, Andreas Dähn carried out the engineering measurement of the facade. This was the basis for the required static calculations with the determination of the fixed and floating points, for the measurements of the facade modules and aluminium profi les and hence also for the arrangement of the vertical expansion joints. The planning was flexible since the refurbishment was carried out in building sections. Therefore, it was necessary to plan a relevant time frame for the section-by-section approval of the sub-structure and module arrangement.

Laser, manufacture, assemble

A decisive factor for the safe function of the facade construction was the exact positioning of the fixed and floating points according to the planning documents. Repeated measurements were made for the planning and manufacturing of the modules after the subsequent assembly of the concealed insulation and the stud holders. A laser device was constantly in use for this purpose. BOEHME^® SYSTEMS manufactured all modules from coil and panel board material in its own professionally equipped factory. Foreman Roland Töpfer was responsible for the professional manufacture and assembly on site. „We only transported all modules to the construction site once all the preparations for smooth operation were made in order to prevent expensive and potentially destructive interim storage on site. The building situation required that the modules had to be transported by hand to the installation location. The assembly itself, however, did not cause any problems due to the precise preparation (mount and anchor). The semi-transparent modules for the entrance areas were made with half the number of aluminium profi les. Therefore, we only assembled every second profi le. We used three millimetre thick aluminium sheets in order to achieve the necessary stability“, Roland Töpfer describes the construction progress.

All tradesmen had to adhere to fixed drilling times since the entire refurbishment was carried out whilst the school was operating normally. Unrestricted working was only possible in break times, after 3 pm and during holidays. „We were prepared for the fixed drilling times. The very extensive concrete refurbishment meant that we could not work all around the facade but only work individually on some building parts. This called for an enormous additional measuring requirement which signifi cantly extended the construction period. At the end, however, we were able to deliver to the building owner in cooperation with the architects Huber and Staudt an architecturally unique and technically polished facade cladding,“ summarises Andreas Dähn.

Klaus Siepenkort/Andreas Dähn

Building blackboard

Project: Metal facade for the secondary school centre for car technology in Berlin

Building Owner: Senatsverwaltung für Stadtentwicklung, Berlin (www.stadtentwicklung.berlin.de)

Project management: Schäfer Architekten Ingenieurgesellschaft, Berlin

Architects / Construction management: Huber Staudt Architekten BDA, Berlin (www.huberstaudtarchitekten.de)

Specialist plumbers: BOEHME^® SYSTEMS GmbH, Boxdorf (www.boehme-systems.com)

Facade work planning: Bauingenieurbüro Andreas Dähn, Dresden

Facade system: curtain-type, heat insulated and rear-ventilated facade cladding

Product: BOEHME^® SYSTEMS Plug-in panel, Type Profil Linear U

Cladding material: Anodized aluminium profile 1 and 3 mm, shade C 32 (Euras Norm), approx. 25 t

Heat insulation: 160 mm concealed and water repellent mineral fibre insulation