Structure of baroque church roofs in Bavaria

The authors report results of an extensive survey of baroque timber roof constructions in Bavaria. It turns out that the majority of these roofs lack a tie-beam at their base, because the roofs harbour masonry vaults which rise high into the roof space. In the church roofs analyzed, different historical techniques have been identified for carrying the thrust of the roof and the vault in the case of a missing tie-beam. We analyze these techniques both from a historical point of view (development and spread of technological knowledge by carpentry treatises) and from a structural point of view, including the structural assessment in an exemplary case. 1 AN INTRODUCTORY CASE STUDY We start from some observations made during an intensive inspection of the southern Bavarian pilgrimage church of Tuntenhausen, some 30 km south-east of Munich. The church was erected in 1628, during the ThirtyYears War. It replaced an older, gothic church, of which only the tower in the west is persisting – a strange twin tower, consisting of two towers built wall-to-wall. The church is one of the earliest “baroque” churches in the area. However, its layout resembles very much the layout of a gothic church. The church has three parallel naves with three bays. The main nave is in fact somewhat higher than the aisles, but the whole keeps the general impression of a “hall” church with three naves of roughly equal height (cf. Fig. 1). The main arches of the church are supported by two pairs of slender pillars. In the east, the church features a chancel with an ambulatory, encircling the partly preserved old gothic polygonal apse with the principal altar. When the authors of the present paper inspected the church, they were confronted with preparations for restauration work, and their opinion concerning wide cracks in the vaults was asked for. It was not clear whether the damage was caused by defects in the roof structure or rather by ongoing settlements. Investigations on the stucco surfaces indicated that the cracks were not new, but had developed with a decreasing rate since the 17th century (Rosenheim 2007). It turned out that the present state of the structure could not be explained without a thorough understanding of its building process, which could be deciphered from observations in the attic space. Quite like the church itself, the roof structure resembles gothic constructions very much (cf. Fig. 2). Figure 1. A view of the vaults of the church atTuntenhausen. Figure 2. Section of the roof truss, Tuntenhausen (1628). Shaded beams correspond to the original structure, blank beams are later additions.