A draft in an older window almost never comes from one place. Air moves through weatherstripping once it has flattened, around the sash where the frame has racked out of square, and straight through the gap between the frame and the rough opening when the original installer packed it with nothing but trim.
House movement does the rest. Foundations settle, headers sag, and a window that was square when the house was built isn’t square now. The sash stops meeting the frame evenly, and you feel it on the coldest night of the year.
Failed glass seals are different. That’s not air movement at all. The insulating gas is gone and the pane runs cold, so the window reads drafty even when it’s sealed tight. Same symptom, different cause.
When the source is the frame or the original installation rather than worn weatherstripping, sealing it again buys a season at best. Our page on replacement windows for older St. Louis homes covers the window types and glass packages we install.
How Do I Find Where a Window Draft Is Coming From?
Run the back of your hand slowly around the sash, the meeting rail, and the perimeter trim on a windy day. Cold moving air shows up at the gap. If the glass itself feels cold but you can’t find moving air, you are looking at a seal or glazing problem, not a leak. Note which windows and which edges, because that tells an estimator where to look.
