June 13, 2014 / Press Release

Muntin bars for the Leipzig Opera House

Gold-coloured Thermix products from Ensinger help ensure refurbishment in keeping with heritage requirements

1000 years of Leipzig: Formerly known as the “City of Lime Trees”, Leipzig is pulling out all the stops to mark its jubilee in 2015. As a landmark trade fair, university and media city, Leipzig also aims to show off its musical credentials. Celebrated composers such as Johann Sebastian Bach, Felix Mendelssohn-Bartholdy, Richard Wagner, Gustav Mahler as well as Robert and Clara Schumann all worked here. And the world-famous Leipzig Gewandhaus Orchestra has a regular stage on which to perform in Europe’s third oldest Opera House.

1960 saw the opening of the present-day Opera House, then the GDR’s most modern theatre located on Karl-Marx-Platz, now renamed Augustusplatz. Its architecture evokes the classical predecessor building, which was destroyed by aircraft bombs in 1943. At the same time, with its austere language of form, this is heralded as one of the most attractive examples of the building style of the late 1950s. 737 large muntin windows with gold anodized aluminium frames lend a light and almost transparent appearance to the sandstone façade.

2700 square metres of muntin windows

“The problems besetting the building were so extensive that in 1998 it was still under threat of closure. But the City Council then voted in favour of refurbishment”, explains Volker Längrich, Construction Supervisor and Head of Building Management at the Leipzig Opera House. “Since then, further renovation and refurbishment work has been carried out in the building during each summer interval: Structural faults have been eradicated, the building technology and fire safety equipment has been modernized and the interior fittings of the auditorium have been renovated in keeping with the original. Another task was replacement of the muntin windows over a surface area of 2,700 square metres.”

Many of the over 50 year-old windows were no longer functional and were letting in draughts. The heat transfer coefficient Uw was just 3.7 W/m²K. The result was low temperatures in winter, while in summer the building overheated, and the sound proofing was insufficient. Renewal of the windows in keeping with heritage guidelines and in accordance with the Energy Saving Act (EnEV) allows the achievement of a Uw value of 1.3 W/m²K, resulting in an estimated 15 to 20 per cent reduction in heating costs, restoring the future viability of the Opera House.

Thermix minimizes thermal bridges

“Operatic artists are like high-performance athletes - so we had to pay attention to the humidity in the building”, explains Dipl.-Ing. Toralf Schmidt, in charge of renovation planning. “But because of the building’s listed status restrictions, we were not allowed to install tilting windows, even in the showers and changing rooms. Now, when required a 5 mm wide joint gap permits ventilation to take place between the window sashes. To prevent condensation build-up at the windows, the thermal bridges in the frame assembly had to be kept as minimal as possible.

The window construction company commissioned for the project, HAGA Metallbau, suggested using Thermix muntin bars and warm edge spacers Thermix TX.N plus from Ensinger between the panes of the triple glazing. The plastic used for this is 700 times less thermally conductive than aluminium, which is used as the basis of conventional spacers. This allowed insulation of the frame assembly to be radically improved. The Uw value of the windows now even exceeds the requirements of EnEV, at 1.1 W/m2K.

New gold-framed windows to mark the jubilee

“Because they permit adjustment of the colour, the Thermix muntin bars and spacers can be ideally used for heritage window renovation projects. A gold anodized aluminium panel on the pane creates the perfect visual impression”, says Mathias Riecke, CEO of HAGA Metallbau in Lichtenau. “Once we had agreed the design with our partners Sachsenglas Chemnitz, Wicona and Ensinger, we were able to complete production and installation of the 340 windows ranging in size from 1.4 times 1.6 to 2.4 metres within just eight weeks.”

“The customer was delighted with the muntin bars and spacers produced specially in a gold colour”, recalls Dr. Albert Lingens, Head of Thermix Sales at Ensinger in Ravensburg. The last stage of the refurbishment project has been announced for 2014: 130 windows are due to be replaced in line with heritage guidelines during the summer interval, and once again these will be equipped with Thermix products. The Leipzig Opera House will be resplendent in time for the city’s 1000 year celebrations following its complete structural and energy-efficient makeover with new gold-framed muntin windows.

Project details:

Renovation of Leipzig Opera House

Europe’s third public opera house was constructed in Leipzig in 1693. Looking back on a rich cultural tradition, this establishment remains highly successful to this day as a venue for opera, the Leipzig Ballet and Musical Comedy: audiences totalling around 170,000 attended the Leipzig performances in 2013, equal to 71 per cent capacity. Capacity increased in the case of opera performances from 51 to 73.8 per cent.

The building constructed in 1960 has been undergoing renovation gradually since 1998. The windows of the east and west façade of the stage building were renovated in 2013.

Project scope:

340 windows of 2.8 sq.m.


Uw value from 3.7 W/m2K to 1.1 W/m2K (required by EnEV 1.3 W/m2K)


Oper Leipzig, Leipzig


Dipl.-Ing. Toralf Schmidt, Engineering Consultancy for Building Conservation, Leipzig

Window builder:

HAGA Metallbau GmbH, Lichtenau

Window profiles:

Wicona Verkaufsbüro Nord-Ost, Leipzig

Muntin bars:

Thermix® muntin bars from Ensinger, Ravensburg


Thermix® TX.N® plus warm edge spacers from Ensinger, Ravensburg

Insulated glass units:

Sachsenglas Chemnitz GmbH, Chemnitz


Rainer Model Montagebau, Pöhl


For more information on Thermix muntin bars:


For more information on Thermix spacers:


Press Contact and Additional Information

Marnie Röder

Ensinger GmbH
Head of Marketing Building Products
Phone: +49 7032 819 244
Mobile: +49 151 624 045 32
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Agency Contact

Oliver Frederik Hahr

oha communication
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About Thermix

Thermix spacers improve the thermal separation of insulated glass windows, doors and facades. This helps save energy and consequently heating and cooling costs as well as cutting carbon emissions. As an insulated glazing edge bond system, Thermix spacers provide a "warm edge". In addition, Thermix muntin bars produce the appearance of a genuine lattice window but with an excellent level of insulation. Both products can be simply and efficiently processed. Specially developed corner keys and straight connectors ensure well-fitting and secure connections every time. Thermix is a brand of Ensinger, one of the leading specialists in high-performance plastics. For more information, go to: www.thermix.de/en

About Ensinger

The Ensinger group is engaged in the development, manufacture and sale of compounds, semi-finished materials, profiles and technical parts made of engineering and high performance plastics through extrusion, machining and injection moulding. With a total of 2,300 employees at 28 locations, the family-owned enterprise is represented worldwide in all major industrial regions with manufacturing facilities or sales offices.

The Leipzig Opera House refurbished and resplendent for the city’s 1000 year jubilee. Picture courtesy of: Kirsten Nijhoff, Oper Leipzig.
The plastic used for Thermix® TX.N® plus spacers is 700 times less thermally conductive than conventional aluminium. Used in combination with gas-tight stainless steel sheathing, a particularly low heat transfer coefficient is achieved, making Thermix muntin bars and Thermix TX.N plus an excellent warm edge solution. Picture: Ensinger, Ravensburg.

Your Contact for Editorial Questions

Jörg Franke

Ensinger GmbH
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