The Assembly of Roof Structures in the Mediaeval Churches of Finland: The Case of Karjaa Church (1470)

Abstract The last still-standing examples of Finland’s mediaeval timber constructions are the roof structures of some 20 stone churches. Karjaa Church — built in 1470 — boasts one of Finland’s best-preserved examples of such structures; it is vital in the country’s wooden cultural heritage. We present our interpretation of the building process of the Karjaa Church nave’s roof structure. Given the lack of written records on church building processes from the Finnish Middle Ages, we have employed a building archaeological approach, also integrating observations from Finland’s other mediaeval roof structures. This is complemented by a secondary-sources review to mirror the more general knowledge on Finnish mediaeval society and estimations of the local population, animals, labour tasks and workdays to understand the financing and labour provided by the local community. The fieldwork (2020/2024) involved systematically documenting the nave’s roof trusses, focusing on the doweled joints and the rafter feet, as well as the deliberate and incidental marks of craftsmanship, e.g. numberings and drill marks. Our findings indicate the trusses were manufactured on the ground in stacks before being dismantled and reassembled at wall-plate level. Evidence suggests that the rafter feet remained intact during this process, whilst other elements were reassembled after transport. Observations of the drill marks and notches reveal construction-technique variations, likely attributable to individual craftsmen’s methods. By analysing structural details and contextualising them within their historical and societal framework, this research enhances understanding of Finland’s mediaeval roof construction, providing foundations for future studies on the material — labour — craftsmanship interplay in historical architecture.