A mathematical model and its analytic solution for the analysis of stress-strain state of a linear elastic two-layer beam is presented. The model considers both slip and uplift at the interface. The solution is employed in assessing the effects of transverse and shear contact stiffnesses and the thickness of the interface layer on behaviour of nailed, two-layer timber beams. The analysis shows that the transverse contact stiffness and the thickness of the interface layer have only a minor influence on the stress-strain state in the beam and can safely be neglected in a serviceability limit state design.