The unstable climate circumstances cause many relevant risks, such as heavy rainfall. In the past, Egypt experienced rainfall over time. Although Egypt is still classified as low perception country, it can suddenly experience extreme rainfall events during the year, resulting in flash floods. Many fragile materials related to heritage buildings' façades may be affected by the change in rainfall rates without any risk assessment plan. In this research paper, the meant risk is the one that occurs in heritage buildings when the vulnerable materials’ façades face the hazards of water drops hits coming from the rainfall. From this point, the need for making a risk management plan has appeared in order to conserve heritage buildings against heavy rainfall. The research methodology depends on the ABC risk assessment quantitative method in addition to experts' multi rounds assessment and then tornado diagrams to analyze the magnitude of risks in order to present a risk assessment plan for a group of heritage buildings in Historic Cairo as a pilot study that can be generalized to similar cases, the final output framed into Ishikawa model for rainfall risk’s problem solving which generated from the rainfall risk causes and effects on the heritage buildings facades.