Hi I have an upstairs bedroom and the floorboards are not in great condition (gaps and not very level). So before we put laminate down I am going to cover the floor with sheets of 12mm ply. Question is, If I screw every 150mm on the ply, do I need to leave an expansion gap around the edges, like I would with the laminate? The laminate will be floating, so no nailing or gluing it. Thanks, Alan.