In this paper we propose a new refined shear deformation plate theory which possesses a series of desirable features, the most salient of which are as follows: (1) loads, which are generally applied on the middle surface of the plate, act on the upper surface of the plate; (2) equations applicable to the calculation of the stresses in isotropic plates which provide the same order of accuracy as several theories with second-order shear deformation effects; (3) a theory, in the classical sense defined, since it gives easy expressions for application to problems in different fields in architecture and civil engineering.