The buildup of condensate is avoided by normalizing the air humidity in inhabited rooms. The negative pressure in a shaft continuously sucks in a small amount of fresh air through apertures of designed dimensions in windows or walls to mix with the air in the room and go out again via the shaft. The air goes out through the roof via a skylight frame (1) and an attachment with cover plate (2) with an edge (3), part of a shaft (4) with slits (5) and a hood (6,7).
