Enhancing residential building energy efficiency has become a critical goal to take up current challenges of human comfort, urbanization growth and the consequent energy consumption increase. In a context of integrated smart infrastructures, sensor networks offer a relevant solution to support building energy monitoring, operation and prediction. The amount of accessible data also opens new prospects to better consider key parameters such as human behavior and to lead to more efficient energy retrofit of existing buildings. However, sensor networks planning and deployment is a particularly complex task facing many challenges and affecting the performances of such a promising solution. The present paper highlights watchpoints from the implementation of an instrumentation solution for the study and evaluation of a deep energy retrofit of existing collective residential buildings. Observations will be grouped in four categories. They will be illustrated with actual field situations and discussed to provide potential solutions for efficient future sensor networks deployment.