ADA Curbless Showers in a Residence

Does anyone know if there is a UPC Code that deals with threshold heights for curbless showers. It seams the ADA guidelines and the UPC conflict, and our county is suggesting I need a 2 inch differential between the height of the walk in area to the shower and the drain. That makes it very unstable for someone in a walker in a 36 x 60 shower. Please help....thank you

See if you can get a copy of the TCNA (Tile Council North America) handbook.