Monitoring activities of daily living (ADL) is a frequent practice to determine the independence of elderly people in their homes instrumented with a set of sensors. To do so, the representation of ADL is an issue that must be addressed. In this paper, ADL representation based on task models is presented. To this extent, we propose an approach for task modelling of ADL by means of HAMSTERS-XL, an extensible task notation and tool allowing the design, visualisation, and simulation of task models. The proposed approach consists of several steps aiming to determine parameters, such as time and location, of both activities and sensors, as well as the events that need to be identified. To demonstrate the suitability of our approach, we present the description of two ADL performed by a resident within a smart home environment by employing the AGGIR grid variables, a tool adopted by the French government for determining the autonomy of an elderly individual. The obtained results are analyzed with the purpose of indicating the advantages of using ADL representation by means of task modeling.