Purpose – The purpose of this paper is to present a critical review of a criterion of risk, created to assess the flood risk of the international heritage building. In order to evaluate this criterion, it was applied to a sample of Portuguese building heritage. Design/methodology/approach – This effort will start with the definition of the most important historical buildings in Portugal, its location and a full study about its constitution considering not only the materials they are made to but also the layers and the influence of the porosity/porometry for the drying process. Then it will also crucial the classification of the flood risk occurrence having in mind the previous information. A mapping will be made with the classification here developed. Findings – This work presents a critical review of the main information related with the Portuguese monuments classified as “National Monuments”. A new empirical model was proposed takes into account all of the factors defined as the most influent in flood risk determination. A risk map was created on the basis classification developed. It will be possible to observe that a significant amount of Portuguese monuments are classified as medium to high risk of flooding. Originality/value – This paper presents a new methodology to analyse the flood risk of international heritage building. The main benefit of the work is that it discusses the importance architectural heritage and justifies the need to safeguard it from extreme climatic phenomena such as floods.