This paper describes the experimental and numerical study of the main building of the Early Childhood Protection Association (APPI - Associação Protetora da Primeira Infância) in Lisbon. The case study pertains to a mixed timber and brick masonry structure featuring an original design dating back to the 20th century. Steel frames were incorporated as part of rehabilitation carried out in 2014. This study intends to: (i) use laser scanning for the on-site data geometric acquisition and develop an H-BIM (Heritage-Building Information Modelling), a comprehensive tool that provides access to various entities responsible for the management and conservation of the building, (ii) identify dynamic characteristics through in-situ environmental vibration tests; (iii) calibrate and validate the numerical model developed for nonlinear static analyses and seismic response simulation; (iv) study the seismic capacity of the building in its current condition, proposing adequate strategies for modelling this type of buildings through an equivalent frame modelling approach and identifying main vulnerabilities. The building was originally regular and then, after rehabilitation, transformed into a non-regular structural configuration in the plan. The developed work highlights the importance of sequence and constructive details for accurate numerical modelling.