Vienna, 1978

Roof truss renovation
Piarist Church
Maria Treu

In 1697, the Piarist order settled in Vienna's Josefstadt district. From 1716, the mighty church was built on the basis of a chapel, probably according to plans by Lukas von Hildebrandt, one of the most innovative creations of the Austrian Baroque. The main dome is adorned with a fresco by Franz Anton von Maulbertsch, one of his major works.

The roof truss, which is more than 250 years old, shows severe structural damage, has already sunk by almost 80 cm and threatens the fresco, which is worthy of preservation. A case for the timber construction specialists from WIEHAG.

Renovation and monument protection

Encountering challenges

The structural damage had progressed so far that the roof truss had to be replaced. The basic requirement for this was to retain the old roof shape, which was part of the listed building structure.

Soon after the contract was awarded, it became clear that the planning - around 7 weeks - and production - around 4 weeks - times specified in the contract would not be sufficient.

The interior of the church has an extremely complicated, cross-shaped floor plan. The centre of the dome-shaped central space forms an almost circular oval with a flat dome, which is surrounded by six side altars. Accordingly, the roof structure is divided into a nave roof, an octagonal tent roof over the main dome and the side roofs over the transepts.

Precise planning

Detailed planning was key

The complicated roof shape, with its multiple intersections, required extremely careful and dimensionally accurate detailed planning and factory production. The exposed height - the eaves are 23 metres above the surrounding terrain - and the tightness of the building site made it virtually impossible to make changes and adjustments during assembly.

To begin with, the old roof truss above the nave and aisles was dismantled down to the collar truss level and a protective roof was erected above it.

The new primary roof structure of the church, consisting of the standard trusses of the nave and the side roofs, the hip and Ix trusses of the central tent roof, as well as the hip trusses and the diagonal trusses of the side roofs, such as the hip trusses above the nave, are constructed with a glued laminated beam system, which was prefabricated in the WIEHAG production facility.

Client: Order of the Piarists
Architecture: Dipl. Ing. Gerhard Lichtblau, Vienna
Surveying and statics: DI Dr Erich Meixner and DI Karl Koncki
Construction period: 1978
Scope of services WIEHAG: Detail statistics, execution planning, production and assembly of the roof truss