The "Ackerbürgerhäuschen" is located in middle Franconia and was built around 1400. The building is listed for preservation and is situated in the old town of Hilpoltstein, which is listed as well. During the renovation of the Ackerbürgerhäuschen in 2016, Monika and Thomas Fritsch set themselves the goal of preserving not only the possibly 1,000-year-old cellar vault, but also the outer wall made of sandstone and the oak beams of the framework and roof truss. The house got the KfW Award “Bauen und Wohnen 2016” because of the excellent energetic renovation.

Architecture

The Ackerbürgerhäuschen has one floor and is connected to the side of the eaves. The entrance door is placed in the middle of the west side. Besides the entrance door there are two windows right and two windows left. The outside walls are built of sandstone, except for a wide piece of wall on the east side – consisting of breeze block. On the southern gable end, there are two windows on the first floor and two on the second floor.

There is also a window in the attic floor. On the east side there are several windows. The north-side gable end has just a door on the ground floor. Under the north-side half of the house there is a barrel vaulting with oriented to the north-south direction. The roof truss consists of a double standing truss with a conveyor in the west-east direction and a knee brace in the north-south direction. The south gable, consisting of sandstone, was original planked. The north gable consists of bricks. The floor on the upper floor consists largely of floorboards.

Aim of retrofit

The renovation should not only preserve a historic building in the listed old town of Hilpoltstein, but also revitalize the old town by creating new living space. The eyesore in the centre of the village should disappear and appear in new splendour. During the renovation, attention was paid to the barrier poverty. This was successfully implemented by a barrier-free sanitary area, the avoidance of thresholds and the installation of barrier-free doors.

Due to the fact that only little usable building fabric was left of the existing building after years of vacancy, an attempt was made to preserve this building fabric as far as possible. In places where it was possible, the original building fabric was brought to the fore. This is particularly evident in the exposed roof truss, which is over 600 years old, the exposed beams on the ground floor as well as the load-bearing beams or the partially exposed natural stone façade in the interior.

Retrofit solutions

External walls: The existing 300 cm thick sandstone masonry could be preserved. Most of the existing plaster was no longer present. The wall area is 44. 18 m². The existing wall was insulated on the outside with a thermal insulation composite system as an energy-saving measure. In the inside a plaster mortar of lime gypsum, gypsum, anhydrite and lime anhydrite was applied.

U-value (pre-intervention) [W/m2K]: 3,211 W/m²K

U-value (post-intervention) [W/m2K]: 0,19 W/m²K

Windows: The existing wooden windows were replaced by old and new windows with similar forged fittings. The documents show that box windows were installed on the ground floor. By installing a 2-panel thermal insulation glazing, the existing building was energized. Due to the identical windows with identical wrought iron fittings, the appearance of the existing windows could be preserved as far as possible.

Existing window U-value Glass [W/m2K]: 0,0

New window U-value Glass[W/m2K]: 0,6

Existing window U-value Frame [W/m2K]: 0,0

New window U-value Frame [W/m2K]: 1,3

HVAC

While most of the neighbour buildings had already been equipped with modern heating systems, the previous occupant, Mrs Fischbacher, was still living in her almost 600-year-old cottage with a charcoal stove for heat. The charcoal stove was replaced by a central heat generation system. The new gas condensing boiler has a buffer tank for domestic hot water storage, hydraulic balancing (KfW confirmation) and insulated pipes in accordance with EnEV. This gas condensing boiler also heats the underfloor heating installed in all rooms. This has an average temperature of 35/28°C. As an additional heating source, a fireplace stove was connected in the ground floor living room. This also creates a pleasant homely atmosphere.

The farmhouse has only a decentralized coal-fired furnace for heat generation. This was replaced by a central gas-combustible heating system, underfloor heating throughout the building and a fireplace stove.

Find more details here.