What an Old House’s Indoor Glass Window Might Mean

Old houses have their own special charm. The fancy architectural details and the cool hidden features like dumbwaiters or secret ironing boards make them super appealing. But you might be a little confused to see a skinny glass window over a door inside an older home, with a view into another room rather than outside. These aren’t just windows that got stuck inside when an addition was built – they actually served some important purposes.

Those narrow, rectangular or arched glass panels over interior doors are called transom windows. Back in the day before air conditioning was a thing, exterior transom windows helped keep the inside of the house cooler on hot days by letting the warm air near the ceiling escape outside. And interior transom windows, even though they’re not as common anymore, can still be pretty useful if you live in an older home. They help improve air circulation and prevent issues like stuffiness, mold, and mildew.

A lot of interior transom windows can be opened and closed using a long rod. And they don’t always have to be clear glass – some have decorative designs. The ones over exterior doors let in more light, but the ones over interior doors also help control the airflow and temperature between rooms. If you open all the transom windows in a house, it can create a nice breezy flow of air.

Back in the 19th century, these interior windows actually served a really important purpose – helping to stop the spread of tuberculosis. TB was a super contagious lung disease that was basically untreatable at the time. Doctors realized that preventing stagnant air was key to controlling the disease, so they pushed for laws requiring better air circulation in crowded buildings. That’s why you’ll often find those tuberculosis-fighting transom windows in older homes – they were an early attempt to keep the air moving and reduce exposure to the deadly illness.

In 1867, New York passed a law requiring tenement buildings to have better airflow. Then in 1879, the law was updated to say that every livable room had to have an outside window or a window connecting to another room with an outside window. So the transom windows were part of that effort to bring fresh air into crowded living spaces and stop TB from spreading.