Under Construction

Building with Prefabricated Concrete Sandwich Elements in the Social Housing Sector
 

Photography: Louai Abdul Fattah

In Vienna’s 22nd district, we are currently building two municipal residential complexes connected by row houses using prefabricated concrete sandwich elements. It is an efficient and systematic method to arrive at a ready-made outer shell in a short construction time, and as such a novelty in subsidised housing construction in Vienna.

Prefabricated composite façade elements save a lot of time during construction and enable high-quality and precise processing of concrete. We already employed this building method for our own office project, the Stadtelefant; now we are realising a residential development in Vienna’s 22nd district following this concept: on Grete-Zimmer-Gasse, two buildings with ten and seven stories respectively are presently being erected, which will offer space for 113 apartments. Likewise, the outer walls of the seven row houses in between are made of precast concrete elements. The outer shell with its premium quality exposed concrete façade is ready to go upon placement – boasting an elegant, honest, and straightforward appearance.

Each custom-made component is pre-produced at the factory of the Lower Austrian company Trepka in Ober-Grafendorf. The sandwich elements are composed of an 18-centimetre-thick load-bearing shell, a 16-centimetre insulation layer, and an eight-centimetre-thick visible cladding, which are each braced to one another with anchors. Wall cavities for electrical outlets are already provided at the intended locations during the production process, together with the required lightning protection, which was also embedded in the concrete before curing. In addition, the finished elements are sandblasted at the manufacturer before delivery – this gives the exposed concrete a high-grade surface texture.

The elements are brought to the construction site by truck. For transport and logistical reasons, one side of each element can be no wider than 3.60 metres, and the maximum length is nine metres. Depending on the size, a single element can weigh around 8.5 tonnes or more. A crane lifts the concrete elements into position, and the workers on site assemble the outer façade floor by floor like a jigsaw puzzle. Laterally, the elements are connected to each other via metal loops; the connection to the floor or ceiling is made using metal spikes and L-brackets. The cladding layer overlaps the concrete slabs, so that only a narrow joint between the prefabricated elements remains visible on the outside of the façade, which simply needs to be sealed properly with silicone.

In the limited-profit housing developer Familienwohnbau, we have a partner on board who is committed to following this innovative approach to prefabrication in the social housing sector. The somewhat higher manufacturing costs in comparison to a conventional construction technique with in-situ concrete and full thermal insulation can be offset by the faster construction time. The façade design is a contemporary interpretation of the mass-produced façades in the Gründerzeit period and represents a high quality alternative to the quite unimaginative thermally insulated plaster façades that currently prevail in Vienna.

The windows are then inserted into the designated openings on site using standard connections. The outer shells of the wood/aluminium windows are anodised in a golden tone, as are the balcony railings, which are mounted at a later point. Together, the exposed concrete façade attains an added, elegant touch of colour.