R702.7

Section R702.7 is titled 'Vapor retarders' and covers the requirements for the installation of materials that restrict moisture vapor from passing through the walls of a conditioned building. The requirement for vapor retarder specific classes, area within the wall assembly that they must be installed, and the climate zones where they are required is established. The purpose of this section is to prevent moisture accumulation within wall assemblies which can lead to mold and premature degradation. This section has 3 exceptions which list walls that are not subject to this section. The purpose of these exceptions is to clarify that since these types of walls don't pose a risk of mold or structure premature degradation from moisture vapor accumulation, that vapor retarders are not required.

The model shows a section of an exterior wall with a sheet of polyethylene plastic vapor retarder installed between the interior side of the framing and the gypsum board.