Interior insulation goes to school
The art nouveau, listed school construction was completed in 1908, when it was seen as a particularly modern school building. It was heated via a low-pressure steam heater and regulated radiators in the window recesses. A central ventilation system in the cellar was used to ventilate the classrooms.
Just over 100 years later, heating and insulation technology has moved on considerably, while energy conservation has become much more important. As a result, a fundamental renovation was planned, supported and sponsored by the Deutsche Bundesstiftung Umwelt (DBU – ‘German Federal Environmental Foundation’).
The exterior walls of the school were made of around 50cm of solid brick, which was plastered on both sides and had a U-value of about 1,5 W/m²K. The ventilation system worked uncontrolled and all the windows were unsealed, while the steam heater warmed the building to 24°C with high losses of transmission and ventilation heat.
Haase, the architectural office, developed a renovation concept that preserved the historical facades and harmonised systems such as interior insulation, heating, windows and ventilation. A large portion of the heating energy saved can be traced back to the interior insulation. Due to the building’s listed status, it was decided to use mineral and surface-active insulating panels made of perlite. The surface-active panels reach a thermal resistance level of 0,045 W/mK. They are able to absorb moisture from the ambient air, store it and then emit it again when the room’s moisture level drops. This also applies to condensate that can form along the layer next to the cool exterior wall in the winter.
The interior insulation in detail
The renovation work was carried out across several periods in order to affect the school as little as possible. Exterior walls were levelled off so that the insulation panels could be fitted. They were cemented, sealed and given gauze reinforcement. As with all the classroom walls, they were then painted white.
The former heating recesses under the windows were filled to level out the walls, while the soffits were given a 6cm coating of insulating plaster, which now merges into the insulation of the panelled wall.
From outside to inside, the wall is now made of lime cement plaster, solid brick, lime cement plaster to level it off, cement glue, perlite insulation panels and a finishing coat. The interior and exterior temperature and humidity were previously calculated in different configurations, but the interior insulation and further renovation measures mean that the U-value for exterior walls has dropped from 1.5 to 0.34 W/m²K and so meets the requirement of the ENEV 2009.
The low-temperature wall heating also saves energy through its radiant heat and forms a condensation-free construction in conjunction with the interior-wall insulation, which is made up of 3-4mm-strong copper pipes. Light in weight, it did not have to be connected to the brickwork and is instead attached to the panels with copper clamps. Finally, it was covered with a gauze-strengthened plaster coating and then heated for the first time. After cooling (around two weeks) the plaster was dry and a second layer could be added, which helps avoid cracks forming later on. The insulation panels were milled out for the heating pipes that run along the skirting.
Optimal conditions in a school (CO2 level below 1,500 ppm) are only created with sufficient fresh air. For the new ventilation system, old fireplaces were used in order to improve the air quality and the cooling at night during the summer. Ventilation is controlled centrally via a machine in the loft and provides over 90% regenerative heat recovery. As the windows can now all remain closed during lessons, sound proofing has been kept to a minimum. In addition, the ventilation system also helps cool the classrooms at night.
The savings made by these renovations are impressive, particularly when considering the size of the building: the work on the building envelope alone – predominantly the insulation – reduce the transmission heat loss by around 150,000 kWh/a. The ventilation system with heat recovery reduces the ventilation heat loss by around 50,000 kW/a, and finally the CO2 emissions are cut by approximately 63,000 kg/a.
Ludwigstrasse. 5, 97421 Schweinfurt, Germany
Hochbauamt Stadt Schweinfurt
Architekturbüro Werner Haase, Karlstadt
DBU Deutsche Bundesstiftung Umwelt, Osnabrück
Dry construction/interior insulation:
Farben Galle GmbH, Schweinfurt
Interior insulation manufacturer and technical consultation:
Knauf Perlite GmbH, Dortmund