To estimate the damage due to floods, damage functions can be used. They associate a level of damage to flood parameters and built assets characteristics. In France, a comprehensive effort has been made for a decade to build damage functions at national level for different types of built assets (dwellings, economic activities, public infrastructures). During this process, floodam, a computer utility, has been developed. It is based on expert knowledge and used to produce damage functions that relate to specific buildings. The present manual explains the purpose of floodam and its principle. Based on version 1.0.0 of floodam, the manual then describes, first at the level of the building components, and then at the building level: 1) how the data used by floodam were collected, 2) how the damage to the components or buildings is modelled, 3) how the input data are organized, 4) the outputs, 5) some examples. The last chapters explain how some features of the building models can be modified to produce new damage functions and the development perspectives.