Orbit distortion due to the floor displacement in the light source building under climatic thermal stress

Diurnal orbit drift in the storage ring was found. It resulted from floor displacement of the building distorted under climatic thermal stress. The building distortion was both simulated by using a computer model and measured with a leveling system. Both simulation and measurement gave a good evaluation of the floor displacement. The orbit drift calculated from the measured floor displacement agreed well with that actually measured with beam position monitors. As a consequence, it was decided to insulate the roof, which made the building distortion much smaller and the orbit drift minimal.<>