How an accurate surface observation can help in the interpretation of an ancient timber structure: the example of the Valdese church in Florence

摘要

The Valdese church of Florence was built in the second half of the XIX century as the Anglican Church of the local rich British community, reaching the actual status of Valdese church in 1967. At present the whole building is showing some conservation problems and in 2010 the Valdese community asked for a diagnostic inspection of the roof timber structure. The church is a three naves building 30 m long and about 15 m wide. The structure supporting the roof is made of 4 robust wooden trusses connected by 7 wooden purlins. The roof structure is not visible from the interior of the church due to the presence of a large flat wooden ceiling with lateral longitudinal vaults covering the naves. The inspection was performed according to the procedure described in the Italian standard UNI 11119:2004. Two wood species are present in the structure: silver fir (Abies alba) for the principal elements and elm (Ulmus sp.) for the king posts and other secondary elements of the trusses. Trusses showed problems due to decay (rot), mainly located at the rafter-tie beam joints where in some cases failures occurred, in spite of their large cross section. The accurate observation of structural configuration, construction details and different kind of surface traces during the inspection revealed a lot of useful information for determining possible past alteration of the original building. For example the introduction of new structural timber elements inside the original trusses (symmetrical posts) in order to reinforce them was clearly linked to the change from the original one-nave to the present three-naves configuration. The accurate observation of the surfaces of the timber elements, i.e. the lecture of the surface finishing, of the quality of the elements, the presence of old nailed joints, the notes left on timber elements by the workers during past, traces of dates, allowed getting some hypotheses about the different building and decoration phases of the church. Somehow connected are also traces of differences between the texture of the walls: some of them are made of different kind of bricks, some others with a combination of bricks and stone. The first Anglican church had the entrance on the opposite side compared to the present one. The roof timber structure was hidden by a lattice work, probably connected to the tie beams. The whole building underwent a deep renovation straddling between XIX-XX centuries: the entrance moved at the present location, the ancient entrance became the apse and the ceiling and the roof were consequently modified.