G2426.4 (502.4) Insulation shield.
Where vents pass through insulated assemblies, an insulation shield constructed of not less than 26 gage sheet (0.016 inch) (0.4 mm) metal shall be installed to provide clearance between the vent and the insulation material. The clearance shall not be less than the clearance to combustibles specified by the vent manufacturer’s installation instructions. Where vents pass through attic space, the shield shall terminate not less than 2 inches (51 mm) above the insulation materials and shall be secured in place to prevent displacement. Insulation shields provided as part of a listed vent system shall be installed in accordance with the manufacturer’s installation instructions.
This section of the IRC is talking about where B-vent passes through a wall. The B-vent should also be kept 2" away from any combustable materials. If the wall is drywall, then that is not considered a combustable material. If studs are present near the opening of the drywall or any NMC, then that would be an issue. Hope this helps.