A louver, also spelled louvre, is an architectural element consisting of a series of horizontal or angled slats or blades, typically fixed or adjustable, that allow the controlled passage of air and light into a building while blocking rain, direct sunlight, debris, and sometimes noise.[1] These devices are commonly integrated into walls, roofs, windows, or facades to facilitate ventilation and shading.[2]

Originating in medieval Europe around 1500 years ago, louvers were initially employed as rooftop structures in kitchens to vent smoke and steam from open fires while protecting against weather elements, often constructed from wood, scrap metal, or ceramic materials shaped into decorative forms like human faces or animals.[3] The term “louver” emerged in the early 14th century, possibly derived from Medieval Latin lodarium or Old High German louba, referring to an upper room or roof feature, and by 1550, it described overlapping slats in windows.[4] Over time, louvers evolved from purely functional vents—such as those used in medieval designs for sound projection in belfries like Sens Cathedral’s (12th century) or for solar protection in 18th-century Demerara windows in Guyana—to decorative and integral architectural components in modernist buildings by the 20th century, exemplified by works of architects like Alvar Aalto.[4][5]