VENTILATION HOUSING

A ventilation housing of the present disclosure includes: a housing; and a ventilation assembly. The housing includes a tubular projection extending to project from an outer surface and internally having a first space communicating the inside and the outside of the housing. The ventilation assembly includes: an internal member being a tubular body having an opening at a first end portion and an opening at a second end portion; a gas-permeable membrane covering the opening at the first end portion of the internal member; and an external member being a tubular body having a bottom, the external member being joined to the internal member with the internal member inserted in the interior of the external member from the first end portion side. The ventilation assembly is fixed to the projection with the projection inserted in the opening at the second end portion of the internal member to make an inner peripheral surface of the internal member and an outer peripheral surface of the projection abut each other. The ventilation assembly has a second space serving as a ventilation path connecting the gas-permeable membrane and the outside of the ventilation assembly in the inside of the internal member, the inside of the external member, and/or an interspace between the two members. A ratio between an area S1 of a cross-section of the first space and a smallest total area S2min determined by comparison of values of different total areas determined at different distances from the gas-permeable membrane, the total areas each being determined for a cross-section(s) of the second space, is 1.0 or more. A ratio between the area S1 and a total area S2out of a plane consisting of a cross-section(s) of the second space taken at a position(s) where the second space is the narrowest is more than 1.0. This ventilation housing exhibits excellent performance in terms of moisture permeation between the inside and the outside of the housing.