Floors or receptors under shower compartments shall be laid on, and supported by, a smooth and structurally sound base. Support for shower compartments shall comply with the following requirements:
1. Plasticized polyvinyl chloride (PVC) sheet shall be a minimum of 0.040 inch (1 mm) thick, and shall meet the requirements of ASTM D4551. Sheets shall be joined by solvent welding in accordance with the manufacturer's instructions.
2. Non-plasticized chlorinated polyethylene (PE) sheet shall be a minimum 0.040 inch (1.02 mm) thick.
3. Other materials of similar durability and water resistance may be used provided they are approved by the buildings commissioner.