A very important task to improve the sustainability of existing structures is to extend their service life especially in terms of resource conservation and sustainability. Therefore, the assessment and the required safety level of an existing structure are of particular importance (condition monitoring).This paper presents how the elements of reliability analysis can be combined with the elements of in-depth testing and monitoring procedures to periodically evaluate the degradation processes due to changing environmental conditions and new building materials. Subsequently, the remaining service life can be continuously updated with the help of semi-probabilistic partial safety considerations.