Where only a parallel approach is provided to the water closet, the clearance shall be 56 inches (1422 mm) minimum, measured perpendicular from the rear wall, and 48 inches (1219 mm) minimum, measured perpendicular from the sidewall. A lavatory complying with Section P102.6 shall be permitted on the rear wall, 18 inches (457 mm) minimum from the water closet centerline.