AbstractA procedure is presented for deriving low‐complexity structural models to predict the global response of asymmetric‐plan low‐rise frame buildings for purposes of class‐level assessment. As a compromise between employing a full‐scale multi‐degree‐of‐freedom structural model versus an equivalent single‐degree‐of‐freedom one, the challenge is to create an idealized 3D structure with few degrees‐of‐freedom that can match the inelastic response of a building for which full knowledge of geometrical and mechanical properties is available. Such a 3D reduced‐order model can offset the computational cost related to performing multiple nonlinear dynamic analyses within the framework of Performance‐Based Earthquake Engineering. To this goal, rules and equations are proposed for achieving equivalence among the linear and nonlinear properties (e.g. mass, stiffness, strength) of the building analysed and the related 3D reduced‐order model. The procedure is applied on a sample of 15 existing reinforced‐concrete frame school buildings, from the province of Foggia in Southern Italy, for which the full numerical models are available. Both calibrated and uncalibrated reduced‐order models are created, exploring the limitations of the proposed order‐reduction in a real‐life case study.