This final work deals with the evaluation of a truss structure and its wooden elements of St. James church located in Brno. The building is enrolled to the list of a National cultural monuments. The aim was to detect the damage done as well as to determine its range to particular elements. The evaluation of a truss was based on a survey made by sensoric and instrumental methods. Two devices were used for these measurements - Arborsonic Decay Detector and Fakopp UltraSonic Timer at which the spike and cylindrical sensors were used. To compare and determine the conformity or differentiation of the above said ultrasonic devices were used statistical analysis of the results. The structure was found infested with wood decaying insects and wood-destroying fungi mainly in tie beams, collar ties and pentagonal purlins. This damage was evaluated and the level of damage was determined together with its range. The result was recorded in drawings (top view plan). This drawing together with other results will serve as a basis for further phase of reconstruction which is planned to be made to this historically valuable structure.