On the site of the former "Altenburg ob Kunstadt", the Burgkunstädter town hall, one of the most beautiful half-timbered houses in Franconia, has formed the town's skyline for over 300 years. In 1689/90, the master of baroque half-timbered construction, Jörg Hoffmann constructed the impressive decorative half-timbered structure on the early medieval masonry base together with master builder Hans Gebelein .

After an inadequate restoration in the 1970s, considerable damage was found on the entire building in 2000. The aim of the overall renovation of the old building was to preserve and emphasise the historical value of this important monument and to equip it for the demands of the present day. All structural measures were implemented in close cooperation with the client and the Bavarian State Office for the Preservation of Historical Monuments.

The hole town hall is listed for preservation. As Burgkunstadt identifies itself with the decorated half-timbered fascade and as it is desgined by a famous master builder, it is espacially worth protecting. In contrast to that, the massiv stone base is protected particularly because of its age.

Conditions of the envelope

After the city hall had been fundamentally renovated in 1978-1980, one already noticed in 2000 that the infill of the framework was partially loose. For that reason detailed examination were carried. The result was frightening. Since the wrong materials were used in some cases during the first renovation, such as bricks for the infill, as well as paint and plaster that was not open to diffusion, moisture and rot, damage occurred especially on the half-timbered construction and the roof.

In addition, the connections of the ceilings and the roof were partially poorly executed; so that the result was a reduction in stiffening. Furthermore, the investigations revealed a pollution burden in the wooden components, which were so drastic especially in the extension, that it was completely torn down and replaced. Another problem was the lack of airtightness, which meant that when it rained moisture could reach into the rooms. In winter, draughts in the rooms sometimes created room temperatures of 15°C.

Aim of the retrofit

The primary aim of the renovation was to repair the damage already done in order to make the room usable again and to prevent future damage. Particular attention was also paid to preserving the ornamental half-timbered facade.

Retrofit Solutions

Windows: The existing box-type windows were completely replaced in the renovation process. In addition, they were equipped with sun protection. From an energy point of view, insulating glazing was to be installed, although this did not comply with the guidelines of the heritage office. For this reason, a classic drawn glass from the Schott company was used for the exterior panes of the insulating glass windows. This is characterised by its uneven surface, which is created by using the Fourcault method in the manufacturing process. So the original appearance of the façade could be retained.

• Existing window U-value Glass [W/m2K]: 3,0
• New window U-value Glass[W/m2K]: 1,3
• Existing window U-value Frame [W/m2K]: 0,0
• New window U-value Frame [W/m2K]: 0,0

HVAC

Heating: Before the renovation, the town hall was supplied with electric storage heating. The two new gas condensing boilers heat both the historic old building and the new extension. The heating system is located in the technical room on the first floor together with the ventilation system.

Ventilation: As a result of the renovation, the town hall received a ventilation system that supplies the administrative rooms on the 2nd floor.

Domestic hot water: Hot water is generated by decentralized instantaneous water heaters.

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