Apartment house Sommergasse 7, Allschwil

The apartment building at Sommergasse 7 in Allschwil, built in 1954, was completely renovated and topped up.

The design envisaged the removal of the existing pitched roof and an extension to the building with a new attic storey in timber construction. To this end, the knee walls were raised by around 1.20 metres and a pitched roof with a roof pitch of 35° was built on top.

The roof loads are transferred from the rafters to one ridge purlin, two centre purlins and the knee walls. Due to the length of the building, the purlins must be supported between the gable walls. Four dormers will be created on each side of the roof so that two separate residential units can be accommodated in the new attic.

The load transfer of the extension had to be selected in such a way that no interventions in the existing storeys were necessary due to the boundary conditions on site. As a result, the loads of the ridge and centre purlins cannot be transferred directly vertically into the existing building. Instead, the purlins are supported indirectly on cross beams, which transfer the loads back to the existing corridor walls via two posts.

In the centre area of the extension, the loads of the purlins are absorbed by load-bearing solid timber walls. For this purpose, the position of the existing staircase walls is taken up from the existing building. In addition, the partition wall between the two adjoining bathrooms is designed as a load-bearing wall disc. This spans as a wall-like support between the outer wall and the transverse wall to the staircase.

The existing wooden beam ceiling above the 2nd floor was checked mathematically and reinforced with additional panelling on the top of the existing beams. The existing foundations were recalculated to ensure that sufficient load-bearing reserves were available for the additional loads.

The earthquake resistance of the building was checked using the push-over method and compensation measures were developed

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