The need for wireless sensor networks is rapidly growing in a wide range of applications specially for buildings automation. In such networks, a large number of sensors with limited energy supply are in charge of relaying the sensed data hop by hop to the nearest sink. The sensors closest to the sinks deplete their energy much faster than distant nodes because they carry heavy traffic which causes prematurely the end of the network lifetime. Employing mobile sinks can alleviate this problem by distributing the high traffic load among the sensors and increase the network lifetime. In this work, we aim to find the best way to relocate sinks inside buildings by determining their optimal locations and the duration of their sojourn time. Therefore, we propose an Integer Linear Program for multiple mobile sinks which directly maximizes the network lifetime instead of minimizing the energy consumption or maximizing the residual energy, which is what was done in previous solutions. We evalu- ated the performance of our approach by simulation and compared it with others schemes. The results show that our solution extends significantly the network lifetime and balances notably the energy consumption among the nodes.