The 3rd Generation Partnership Project (3GPP) has proposed recently the Integrated Access and Backhaul (IAB) to simplify the deployment of new base stations, where the connection between the User Equipment (UE) and the Core Network (CN) is provided by a multi-hop 5G wireless connection between the IAB nodes. The main contribution of this paper is to propose a cell selection policy specific to IAB, that aims to guarantee the lowest possible total transmission bandwidth cost (including the backhaul cost which is a significant factor in an IAB context) while respecting the base stations capacities, in order to boost IAB network capacity. In this context, a comparative performance study is performed between our proposed policy and state-ofthe-art policies. System level simulation results show that our solution provides the best system capacity via a trade-off between spectral efficiency and load balancing.