Flachgasse, Vienna (AT)
Further construction, Historic preservation

Client: Dietrich Untertrifaller Architekten ZT GmbH
Location: A-1150 Vienna, Flachgasse 35-37
Architecture: Dietrich Untertrifaller
Construction: 2006 – 2007
Area: 550 m²
Programme: Roof structure with 6 flats, office and meeting rooms on the ground floor

Photos: Bruno Klomfar

Team
Thomas Weber, Christian Wolff

Text: Gerlinde Jüttner

Partners
Statics: JR Consult, Graz
Building services: Synergy, Vienna
Building physics: IBO, Vienna

Awards

wienwood 15, Award

Timber construction on a factory roof

The listed former Grünwald metal goods factory from 1907 is one of the oldest reinforced concrete buildings in Vienna. The spacious industrial building houses our Vienna office on the ground floor. On the former flat roof, we have erected a two-storey timber construction with flats. The reinforced concrete structure was barely capable of bearing any additional loads. Vertical load transfer was only possible via the air shaft and the firewalls.

The low weight of timber and the ability to prefabricate and quickly assemble wall and ceiling elements provided the best conditions for the roof structure. The complex construction of overlays, discs and panels thus stands out from the majority of Viennese roof structures, which are made of steel with timber infills.

Discreetly reset

Viewed from the outside, the roof structure is discreetly set back from the façade. This emphasises the historic railing construction at the top. The timber construction is clad in copper-plated, perforated stainless steel sheeting where it is not interspersed with large window strips. This trapezoidal folded sheet metal fits in wonderfully with the charm of this early industrial building.

Complex support structure

To allow the living area on the second attic floor to open out onto the terrace without supports, the roof above is also held in place by two glulam beams that rest on the cross-laminated timber walls. Strictly speaking, the roof structure has three levels, whereby the third floor is only defined as the roof exit. Once the extension work was complete, the complex load-bearing structure was completely absorbed into the functional floor plan, with generous window walls making the intellectual and constructional effort forgotten.

On the first attic floor above the uppermost existing ceiling, all ancillary rooms are housed in a rigid, rectangular timber channel. It supports the ceiling to the second attic storey and serves to brace the two-storey cross-laminated timber walls, which rest on the centre wall and light shaft. The ceiling to the second attic storey cantilevers widely on both sides. On the street side, it is supported by an approximately two-metre-high overhang and on the courtyard side it is additionally supported by three thin steel columns.

The uppermost roof terrace between the longitudinal beams offers a view to the south of the imperial axis of Schönbrunn Palace and the Gloriette.

Our office on the ground floor

The spacious structure of the former factory from 1907 proved to be ideal for our Vienna office. Elements of the historic building create a specific spatial atmosphere that benefits from the dialogue with the sparingly used contemporary elements.