R408.1

Section R408.1 is titled 'Ventilation' and covers the requirements for providing air movement in the space between floors and earth (not including basements). The requirement for openings to the exterior, net opening size to under-floor area ratios (in each case where a class 1 vapor retarder is and isn't installed), and the minimum locations for openings is established. The purpose of this section is to prevent the premature degradation of wood framing and sheathing from excessive moisture.

The model shows a dwelling foundation with vent openings installed where there is no vapor retarder installed; and the same foundation with a reduced amount of vent openings as allowed with a class 1 vapor retarder installed. The vent opening manufacturer's specifications are needed, to determine the net opening area of the product. Different products designed for the same size gross opening will have varying net opening sizes depending on the construction.