The paper deals with the experimental analysis focused on the determination of strain in wooden building structures using optical fibers with FBG sensors. Firstly, optical fibers were used to measure displacements of layers and surface strain of the lower surface of the ceiling panels made from mechanically jointed cross laminated timber (CLT). The measured displacement values of the optical fibers were compared with the results obtained from the inductive displacement sensors. Secondly, optical fibers were used for long-term monitoring of the roof structure of the sports hall. The fibers were mounted on chords of timber trusses and their correct function was verified by a load test.