A ventilation assembly for ventilating an attic of a building through an opening in the roof or wall of the building. The ventilation assembly includes a vent structure having a mounting portion securing the vent structure to the building over the opening. The vent structure further includes a vent portion having a series of walls defining a series of unimpeded fluid passageways for providing unobstructed fluid flow through the vent portion over the opening. The ventilation assembly includes a partially porous membrane mounted to the roof or wall over the opening and spaced from the fluid passageway to maintain the unobstructed fluid flow through the fluid passageway. The membrane also creates a barrier for preventing the intrusion of particles, debris, insects and the like into the opening while allowing the ventilating to occur. The ventilation assembly may also include a series of ribs defining, a series of troughs disposed between the upstanding walls for directing a flow of material away from the ventilation assembly while allowing the ventilating to occur.