We have a residential project that has a garage wall next to the addition. We have 5/8" gyp. board on that common wall. There is a washer and a dryer in the garage. The contractor has run a 2" ABS vent through the fire wall into the attic above the addition, and apparently there is an ABS drainage pipe going through the fire wall also. The inspector says this has to be metal.

Looking in the 2007 CBC (basically the same as the IBC), in Section 406.1.4, in part 2 it does say that "ducts penetrating the walls or ceilings separating the dwelling unit from the garage shall be constructed of a min. of 0.019-inch sheet metal" however the ABS is not a duct. If we do need to have metal on it could we wrap the section of the ABS with a sleeve of the sheet metal?