Have a Building classified as a Type IIB building, using steel studs for interior walls. Contractor wants to put full sheets of OSB sheathing against the studs in the bathroom and behind the cabinets in the kitchen/snack area, as use it for "blocking", for attachment of the cabinets, grab bars, mirrors, and wall hung sinks. He then will put 5/8" gyp. bd over the top of that for the finish.
Is that allowed? I cannot see anything definite under the IBC 603 exceptions that clearly defines that or not.