Abstract: A window or door assembly has spaced apart glass panes perimetrally sealed in sash members which include one or more breathing passages extending from a groove in the outer face of the sash through to the space between the panes. An elongate flat plate, with fine perforations, has perpendicularly extending, reduced width parallel end flanges configured to pilot into and seal off the groove on opposite sides of a passage, to provide an air circulation manifold under the plate. Preferably the plate is nailed in place.