The Chilean Construction Chamber Building has been instrumented with 12 accelerometers for ambient and seismic events since 1995. The structure is a 22 story reinforced concrete building structured with shear walls resting on gravely soils. More than 15 low level and moderate seismic events and several ambient vibration records have been recorded in the structure. One of the records is a continuous ambient record of 6 month. Area temperature, humidity, rainfall and wind velocity have been recorded together with local building vibrations. From these records the dynamic properties are identified using parametric and non parametric system identification techniques. Despite no damage has occurred the predominant modal frequency varies nearly 4% in average and damping also changes by more than 100% for earthquake events. For ambient vibrations frequency variations are in the order of 1%. The results give an initial indication of possible modal properties variations for non damaged typical reinforce concrete buildings.