This paper contributes information about the influence of openings in cross laminated timber (CLT) floors in serviceability limit state (SLS) design. SLS verifications according to the European structural design standard for timber structures-Eurocode 5-comprise functionality, appearance and the user’s comfort. The verifications are based on deformation and vibration criteria. The investigation presented describes the influence of openings on the basis of experimental and theoretical investigations. Rectangular centralized openings in CLT elements were tested. The experimental results were used for the calibration of the numerical models used for theoretical investigations.The numerical models were geometrically parameterized. Towards application for practice, modification factors were derived to enable determination of the respective deformation and first natural frequency.