Earth constitutes an attractive building material, not only for its eco-friendly characteristics but also for its hygroscopic qualities. In order to understand the influence of this quality on an earth brick interior wall, a comparison was drawn between earth and plaster interior walls. For this purpose, a numerical model was developed to evaluate the coupled hygro-thermo-mechanical behavior of the earth brick material. A scenario simulating a one-year T4-type house occupation in terms of indoor and outdoor temperature as well as moisture was studied. This house has four rooms: a living room and three bedrooms, plus a kitchen, bathroom, and toilet. The thermal, hygroscopic, and mechanical characteristics of the material were experimentally assessed to provide input into the numerical model. The one-year numerical simulation shows that the earth brick partition walls play a significant role in the hygrometric comfort in comparison with the plaster partition walls. In addition, it was observed that dynamic changes between the wall and the external environment generate more intense water transfer mechanisms in the first layer of the wall, which exposes it to critical situations that exceed the failure criterion.