Prevention of failure of heritage buildings through diagnostic testing using the example of testing of roof structure elements from the 15th century

• A structure made of fir timber from a single felling in the spring of 1427 was examined. • Surface scans of the test pieces were conducted using an ultrasonic tomograph, along with spot tests: a sclerometric test and ultrasonic tests utilizing: one measuring the velocity of the transverse wave along the fibers and the other measuring the velocity of the longitudinal ultrasonic wave across the fibers. • The article aimed to demonstrate the effectiveness of various diagnostic methods for identifying defects in heritage wood. • The best results were achieved using an ultrasonic tomograph. Structural timber elements in historic buildings very often require urgent restoration. The choice of repair methods always depends on the results of diagnostic tests. Restoration methods and diagnostic testing methods in historic buildings must additionally meet the requirements of conservationists. A high degree of interference with the historic structure is not possible and the diagnostics of structural elements can only be carried out using non-destructive in situ testing methods. The results of these examinations form the basis for further decisions related to restoration measures. The aim of the research presented in this article is to analyze the condition of historic timber resulting from diagnostic studies of roof truss elements in a 15th-century church in Sieroty in Poland. The research was carried out in accordance with conservation recommendations. Selected elements of the roof truss were subjected to semi-destructive and non-destructive testing. Surface scans of the test pieces were conducted using an ultrasonic tomograph, along with spot tests: a sclerometric test with a wood hammer and ultrasonic tests utilizing two devices—one measuring the velocity of the transverse wave along the fibers and the other measuring the velocity of the longitudinal ultrasonic wave across the fibers. The moisture content of selected truss members was also measured. The article aimed to demonstrate the effectiveness of various diagnostic methods for identifying defects in heritage wood. The study concluded that semi-destructive and non-destructive methods can be used for the qualitative assessment of timber in historic buildings. The best results were achieved using an ultrasonic tomograph. Devices that enable single-point measurements can also identify areas of biological damage, structural discontinuities, and assess the impact of internal defects on wood quality. However, their effectiveness largely depends on the density of the measurement grid. The research presented shows that, due to the way the equipment used works, it is best to use several testing methods simultaneously.