When tile roof systems are installed on steep roof structures, 1″x2″ wood baton strips are utilized to help hold the tiles in place during installation and provide a walk able surface. Some roofers use batons on all roofs because it keeps the tiles off of inferior underlayments. On roof pitches under 6:12 there isn’t enough slope to prevent the water from sitting behind the batons and finding the thousands of underlayment nail holes used to hold down the batons. This is referred to as water backup. It is also acceptable to nail down batons and then screw the tiles into the batons. This does not provide the intended wind uplift.