Ventilation is important in dairy barns because otherwise their high humidity would lend itself to the growth of mold and bacteria. That's why dairy barns aren't heated, even in the dead of winter. The Nordic Farms barn in Charlotte uses prefabricated metal vents. Older barns simply had cupolas, whose floors could be opened or closed to control the upward flow of heated air. When I was young, my brother turned the cupola of our historic horse barn into a cabin three stories up, from which he could watch the neighborhood and the sunsets, and where he could sleep if it wasn't too hot or cold.