The seismic vulnerability assessment of existing structures is crucial issue for protecting architectural heritage and planning territorial seismic risk mitigation. The development of the reinforced concrete in the past years led to the creation of well-defined construction type and the establishment of these such as the one discussed in this study. The paper focuses on the seismic vulnerability assessment of a specific reinforced concrete 2D frame, the so-called cathedral portal frame. Both elastic and limit analyses are applied to evaluate seismic vulnerability of the cathedral frame, offering an easy, fast and efficient method tailored to these typological buildings. This approach allows to determine the linear-elastic and non-linear behavior of these structures subjected to seismic forces in a simplified manner. Also, it provides a primary yet efficient evaluation of the seismic vulnerability for this church buildings type, even on a large scale.