The International Residential Code has determined that starting in 2006, paper faced greenboard will no longer meet its standards as an approved tile backer substrate for wall tile in wet areas such as tub and shower areas. The revised IRC code will continue to approve glass mat gypsum backers that are in compliance with ASTM C 1178 and installed in accordance with manufacturer recommendations for use in wet areas. Details of the upcoming code change can be found in section R702.4.4 of the International Residential Code.